Banshee jetting FAQ
Everything you ever wanted to know about Banshee jetting! While the specifics listed are based on the Banshee's stock carbs, the principals remain the same and are similar for other carbs (and anything else with a carb). I'd like to thank all the past and present members of BansheeHQ.com for all their valuable help and input. I've tried to cover as many carb issues as possible, from the most basic to the more complex, so some of you may want to skip ahead (go straight to Q#12 if you want to dial in your mains), and others are welcome to add anything that I've missed or have yet to learn.
First off, here's an excellent link to Carb Theory 101, showing the basics of what does what in the carb:
Also, here's a link to Meat's page with some great carb info and
Next, here's the carb specs for a
'87 and up Banshee:
Mikuni VM26SS roundslide
Pilot jet size:25
Needle clip:Middle (clip #3 of 5)
Main jets are standard Mikuni small hex mains, available from most bike shops, and come in increments of 10 (210 is one size larger than 200, etc.)
Pilot jets are Banshee-specific, only available from a dealer or a knowledgable shop, and are available in
increments of 2.5.
Yamaha pilot jet part numbers:
Now some basic q & a:
Q#1:Why is proper jetting important?
A#1:Depending on your priorities, proper jetting will get the most power out of your motor, and prevent premature wear (which can quickly lead to failure on a high-revving 2-stroke like the Banshee).
Q#2:What happens when my Banshee isn't
A#2:If the jetting is slightly lean or rich, the most you'll suffer is a loss of performance. However, if the jetting is way too lean or rich, your Banshee will overheat rapidly resulting in melted or seized pistons (which is the ultimate "bummer" for the 2-stroke motor).
Q#3:What does "rich" and "lean"
A#3:Rich refers to having more fuel per volume of air in the intake charge entering the motor than the perfect combustion ratio. Lean refers to having less fuel per volume of air than optimum.
Q#4:So how do I know if I'm too rich or
A#4:Your best, most definitive means of identifying a rich or lean condition is by reading your spark plugs (see Q#37). Eventually you'll get a good "feel" for the jetting of your own bike, at least if you ride it often enough and hard enough.
Q#5:How do I correct a rich or lean
A#5:Jetting, of course. Jetting in itself refers to the process (mostly trial & error) of adjusting your carbs to get as close as possible to the perfect air/fuel ratio. Typically this consists of changing the main jet to a larger (or smaller) size, changing the pilot jet size, adjusting the airscrews, and adjusting the needle clip position. Sometimes it can involve adjusting the idle speed, synchronizing the carbs, replacing the needles, and adjusting the float height. Don't worry, it's not as hard as it sounds!!! Most importantly, don't get frustrated, take your time, and don't be afraid to ask for help. Carbs can be confusing, and nobody was born with the knowledge required to tune a single carb, let alone two of them. If you have some basic problem-solving and screwdriver-turning skills there's no reason to let anyone else touch your carbs, EVER!
Q#6:I think my jetting is lean or rich,
what do I
A#6:First, make sure jetting is the problem and not something else; a Banshee can exhibit symptoms of rich jetting without that being the actual cause. For example, a dirty or clogged air filter will restrict airflow, resulting in a rich air/fuel condition. Rejetting in this case could solve the immediate problem (rich condition; poor performance), but could result in a lean condition if you cleaned the air filter and didn't rejet back to where it was (plus that's twice as much work as just cleaning the air filter in the first place). ANY mechanical/electrical problems need to be addressed or ruled out first before altering the jetting (air leaks, torn boots, clogged filters, shorts in the wiring, TORS system faults, bad grounds, water in the fuel, bad fuel, bad bearings, worn rings/pistons, etc.). This is because some mechanical and electrical faults can mimic or cause poor running which could otherwise be contributed to bad jetting. If you're certain that the jetting is the problem, the process would be:
1.determine if the condition is rich or lean
2.identify which carb circuit(s) is the problem
3.correct the problem circuit(s)
4.verify that rejetting solved the problem
Q#7:What are some indications that my
A#7:A slightly rich condition will result in noticeably reduced performance, or "bog". Say your main jets are one size too rich, it starts and runs fine, but whenever you have the throttle pinned (or Wide Open Throttle=WOT), the motor doesn't continue building RPM; it bogs down because there's too much fuel per volume of air and it cannot burn efficiently. Other indications of being rich are fouled plugs, thicker than normal exhaust smoke when the motor is fully warmed up, and the dreaded overheating. Be careful of these symptoms though, as any of them alone may point to a non-jetting related problem (thick white smoke is more likely a head gasket leak, fouled plugs could be a weak stator). While overheating due to a rich condition is not common on Banshees (typically the plug will foul and not fire before it gets too hot), it's still not a good idea to run for extended periods with the jetting too rich. Periodically reading your spark plugs is a good way to get an idea of your overall jetting; if the center electrode (the part that's snow white when brand new) and base ring are light chocolate brown, you're jetting is perfect (slightly rich); if it's black and wet, you're too rich. Doing a plug chop will tell you for sure if your mains are too rich or lean (more on this later). Another trick is to warm up the motor, pop the choke out to the first notch, and ride it; if it bogs worse with the choke out you know you're too rich. Some motor mods will cause a rich condition, as well as changes in temperature or elevation (see Q#13, 14, & 15).
Q#8:What are some indications that my
A#8:A slighly lean condition can result in a hesitation, missfire, or revving high & fast with no power. Say your pilot circuit is lean, when you start it up with the choke "on" it's fine, but when you turn the choke off it idles very high; there's more air per volume of fuel so it burns hotter (in this case airscrew adjustment may solve the problem). Other indications of being lean are a backfire and rapid overheating. Overheating alone will cause serious problems, so even a slighly lean condition is usually much worse than being too rich. Like rich conditions, lean indications may not necessarily mean that jetting is the problem; an air leak between the carbs and the cylinder can exhibit the same symptoms as lean jetting, often if this is the case only one cylinder will act lean. Never take a lean condition lightly, as it's the quickest way to damage your motor. Again, spark plug color is a good indication of overall jetting; if the center electrode remains white or light gray and the base ring shows not coloration after riding for more than half an hour (starting with fresh plugs-if the plugs were already brown for correct jetting they will not turn back to white if it's now lean), it's too lean. A plug chop will tell you for sure. The choke trick is an easy way to tell also; when the motor is warmed up, pop the choke out to the first notch, and ride it; if it runs better (no hesitation or revving high & fast with no power) then you know you're too lean. Most motor mods that improve airflow will cause a lean condition (remember more air per volume of fuel=lean), and will require rejetting richer. Temp and elevation changes can also cause a lean condition (see Q#14 & 15).
Q#9:OK, I'm sure it's rich or lean, how
do I know
what to change?
A#9:For a breif recap of the Carb Theory 101 link mentioned earlier; the carb delivers fuel depending on the throttle position:
0 to about 1/8 throttle is controlled by the Pilot jet size, and fine tuned by the airscrews
1/4 to 3/4 throttle is controlled by the needle taper & length, fine tuned by the clip position
3/4 to WOT is controlled by the main jet size
Once you know which circuit or circuits are rich or lean, you can begin to dial in the jetting.
Q#10:I have a bog or hesitation right off
an erratic idle, OR a very high or low idle...
A#10:Since the problem is between 0 and 1/8 throttle, the pilot/airscrew circuit may be rich or lean, and you may need to also adjust the idle speed screws and check the carb synchronization (see Q#23 & 24). Start by adjusting the airscrews; on each carb turn them in (clockwise; which is richer) a half turn (180 degrees); adjust both airscrews the same amount. If you have the motor idling allow about 20 seconds for the motor to react to the new setting. If the condition gets worse, try going out (counterclockwise; which is leaner) on the airscrews and see if it improves. If going in on the airscrews helps but the problem persists after you turn the airscrews all the way in, or to within a half turn out from seated (don't torque the airscrews! the tip is pointed and overtightening them can cause damage!), try the next size larger pilot jet, and start over with the airscrews 1.5 turns out; tune the airscrews from there to get a clean idle and off-idle response. Conversely, if going out on the airscrews helps but the problem persists after you get to about 3 turns out from seated, try the next size smaller pilot jet and start over with the airscrews 1.5 turns out; tune the airscrews from there to get a clean idle and off-idle response. Once you acheive a clean idle and crisp off-idle response (no bog or hesitation right off idle), you may need to adjust the idle speed up or down by adjusting the idle screws. If airscrew adjustment does not have any affect on the bog or hesitation, and you are certain the problem is below about 1/4 throttle, check the carb sync, make sure the pilots aren't clogged (it only takes a speck of dirt to block the tiny passage), and insure that both airscrews are set the same number of turns out from seated. Be advised that the stock Banshee carbs have a pilot jet that is specific to Banshees; a standard Mikuni pilot jet will not work (see next section for pilot jet details). To verify your pilot/airscrew circuit jetting, start the motor and let it warm up fully; install fresh spark plugs, start it (without using the choke) and let the motor idle for about 10 minutes; pull the plugs and look at the center electrode and base ring; they should be a light chocolate brown color if you're dialed in. As a side note, since the pilot jets are flowing fuel throughout the throttle range (they are solely responsible for mixture at idle to about 1/8 throttle but continue to deliver fuel above 1/8 throttle) changes made to the pilot jet size MAY have an affect on the main jet jetting; if you change pilot jet sizes it's a good idea to verify your mains as well, and to a lesser extent the needle clip position.
Q#11:I have a bog or hesitation at about
A#11:Since the problem is between about 1/4 and 3/4 throttle, your needle clip position may be rich or lean. If you know the jetting in this range is too lean, move the needle clip down one clip position (richer-moving the clip towards the pointy end of the needle). If you're sure it's rich, move the clip up one clip position (leaner-moving the clip towards the blunt end of the needle). If you're not sure if you're rich or lean, try the choke trick; with the motor fully warmed up pop the choke out to the first notch and see if the problem gets better or worse; if better then try going a slot richer on the needles; if worse try going a slot leaner on the needles. Remember to check the carb sync whenever the tops are off the carbs, and don't get the slides reversed; the cutout on the bottom of each slide should face the airbox.
Q#12:I have a bog at WOT, OR it revs high
fast with no power at WOT...
A#12:Since the problem is at WOT, your main jets may be rich or lean. Since the motor is spinning so fast (usually) when the throttle is pinned, the main jets are the most critical circuit on a Banshee; running too rich or lean on the mains can be extremely hazardous to your motor's health: rapid overheating combined with high RPM's are a recipe for disaster. If you have done mods that affect airflow, start with the manufacturer's recommendations or those shown below to get a ballpark number on your main jet size. Similarly, if the temperature or elevation has changed use the below guidelines to get your mains close (see Q#14 & Q#15). Once you think you are close to the right size on the mains, one method of dialing in the main jets is to start with large mains; if it bogs at WOT drop a size until it revs out clean; if it doesn't bog at WOT go up a size until it does and then drop one size. The bog at WOT is usually an indication that it's rich on the mains, however since running lean is usually worse than being a little rich, the choke trick can be used to make sure before you go leaner on the mains: with the motor warmed up pop the choke out to the first notch; if the bog at WOT gets worse you know you're rich and can safely drop a size on the mains; if it gets better with the choke out you're lean and should start going up on the mains until it bogs at WOT, then drop a size. Another method is doing a plug chop (see Q#33), but since you will be revving the motor out in 6th gear it's best done to verify the mains after you have gone down one size from bogging at WOT as detailed above. When dialing in the mains it's best to err on the side of rich than lean to avoid any damage to your motor (rich symptoms are fairly obvious in the form of decreased performance, and can be remedied before engine failure-lean indications may not be apparent until it's too late). Don't be afraid to go big on the mains, as long as you work your way down to the point that the motor revs out clean all the way to WOT you'll be less inclined to risk damage from running lean.
Q#13:My jetting was perfect a couple
months ago and
now it won't run right; why?
A#13:If the outside air temperature has changed by more than 10 or 20 degrees Farenheit since it was jetted perfectly, you'll need to rejet to compensate. If this is the case, typically you will need to rejet the mains a size smaller (if it was dialed in for colder weather) or a size larger (if it was dialed in for warmer weather), and possibly adjust the airscrews. If the temp has NOT changed, and you have not added any other mods or made any changes that could have affected the jetting, your problem could be as simple as cleaning the air filter to needing a fresh topend, before you alter the jetting rule out any other possibilities.
Q#14:Why do temperature changes affect my
A#14:Since the carbs deliver fuel dependent on throttle position, they cannot compensate for changes in air density (only volume). As air gets colder, the molecules become closer together in a given volume (higher density); cold air contains more oxygen than the same volume of warm air. More oxygen in a volume of air means that the same jet sizes will not deliver enough fuel to burn the oxygen at the highest efficiency, and what results is a lean condition (just the same as if you decreased a jet size). On the flip side, as the air gets warmer the molecules are able to expand (lower density); so there's less oxygen in the same volume of air. Less oxygen in a volume of air means that the same jet sizes will deliver too much fuel, and the net result is that you'll be running rich. What that all translates to is that colder weather will require jetting larger (usually just the mains), and warmer weather will require jetting smaller. Going from colder weather to warmer weather will usually result in a bog at WOT (see Q#12), and when this happens you can simply go a size smaller on the mains (and possibly need to adjust the airscrews, see Q#10). Going from warmer weather to colder weather may or may not give you any indications that you're too lean (it may even run better; the highest performance is on the ragged edge of too lean, however this is also where you can risk damage from overheating rapidly). Mikuni says that a main jet size is good for approximately a 30 degree F temp range. While true for a stock machine, as you add mods the temp range that a main jet size works best for may be as little as 20 degrees F (for example: 310 mains for 40-60 degrees F, 300 mains for 60-80 degrees F, etc.). If there's any doubt (especially if there are any indication of lean jetting; see Q#8), dial in the mains again (see Q#12) or do a plug chop.
Q#15:Why do elevation changes affect my
A#15:In the same way air temperature changes the density of oxygen in a given air volume, so do elevation changes. As the elevation above sea level (0') increases, there is less oxygen per volume of air (lower density). Typically you'll need to rejet your mains one size for every 1500'-2000' elevation difference; jet smaller when going to a higher elevation and jet larger for going to a lower elevation (for example: 300 mains at 3000', 320 mains for 0' or sea level IF the temp is the same). Bear in mind that you'll need to compensate for BOTH temperature AND elevation changes, so going from a hot low elevation to a cold high elevation may net no jetting change. Much like temp changes, going from a low elevation to a higher one of the same temp will exhibit a bog at WOT because it's rich (dial in the mains-see Q#12); going from a high elevation to a lower one may or may not give you any symptoms of being lean before damage occurs. While there are other atmospheric factors that can affect jetting (like humidity, barometric pressure, etc.), temperature and elevation changes will have the most drastic affect.
Q#16:Why do premix ratio changes affect
A#16:Just like temperature and elevation changes, altering the amount of fuel delivered by the carbs in a given volume of air will result in a rich or lean condition. By changing how much oil is in the premix, you also change how much fuel is available to burn. Since the oil in the premix is intended to lubricate the crank, it is burned off in the combustion process; however the oil that's in the oil/fuel mixture displaces the amount of fuel that is available for the air to burn; more oil means less fuel and less oil means more fuel, from an air/fuel ratio standpoint... For example, you change your premix ratio from 32:1 to 100:1, every gallon of fuel will contain less oil, so more fuel; from an air/fuel ratio standpoint there is more fuel to be burned so your jetting will be too rich and you'll need to jet leaner. In contrast, going from 40:1 to 20:1 means that every gallon of fuel will contain more oil, so less fuel; the air/fuel ratio will be too lean and you'll need to jet richer. Basically a higher ratio will require leaner jetting and a lower ratio will require richer jetting. On a side note, changing your fuel octane should not affect jetting.
Q#17:Why do some motor mods
require rejetting and others don't?
A#17:Whenever you alter the amount of air flowing in or out of your motor, you'll need to rejet to compensate. More air flowing in from a more efficient air filter will result in a leaner air/fuel ratio; more air flowing out from more efficient pipes will do the same thing; in both cases you'll need to rejet to compensate (typically larger mains and sometimes larger pilots as well, depending on the mod). In addition, mods that affect how efficiently the air/fuel ratio can be burned will also require rejetting (some ignition system mods for example). Changes to compression ratio typically don't require rejetting, however octane requirements often will change and are even more critical to preventing motor damage.
Q#18:Specifically what mods
will require rejetting?
A#18:Pipes & silencers, air filter(s), removing the airbox snorkel, removing the airbox lid, reeds, reed cages, reed spacers, ignition advance, aftermarket coil(s), aftermarket CDI, porting, some aftermarket pistons that alter the port timing, altering the premix ratio (see Q#16), and obviously changing carbs.
Q#19:How much do I need to change my
jetting for a
A#19:It depends. With the multitude of combinations of mods, along with the many variables from machine to machine and location to location, it's impossible to know anyone's exact jetting. However, it is possible to get close; your first resource is contacting the manufacturer (pipes, for example) or machinist (porting, for example) to get a rough idea or baseline for your jetting; next is to inquire about the jetting other people have for the same or similar mods, if possible (keep in mind that other mods, temp, and elevation differences will be a factor); post in the jetting forum at bansheehq.com; or use the rough estimates in the next section.
Q#20:I need to rejet
mains, how do I do it?
A#20:Start by making sure your Banshee is clean, specifically around the carbs. Turn the petcock "off" at the tank, and disconnect the fuel line at the first carb you're rejetting (do one carb at a time so that the bowls and/or slides don't get reversed). Remove the choke hose, located between both carbs (just on the other side of the choke knob on the left carb). Disconnect the bowl overflow line at the bottom rear of the carb. Using a small phillips-head screwdriver, loosen the hose clamp on the black rubber boot at the front & rear of the carb. Push the body of the carb rearwards, compressing the airbox boot, until the front of the carb clears the front reed cage boot, then twist the front of the carb outwards and pull the carb free of the airbox boot. Stick a rag on the top of the motor right under the carb to catch any fuel that's in the float bowl. Using the same small phillips-head screwdriver, remove the four screws that hold the float bowl on (don't lose the two little metal guides for the overflow hoses). Gently remove the float bowl straight off the carb body; if it doesn't come off easily tap the sides with the end of a screwdriver, just don't pry on the gasket mating surface or pull it off at an angle. Once off, check the bowl gasket, it will usually stay stuck to the carb body but it doesn't hurt to check it for tears, or remove the gasket to clean it and the upper mating surface. After the bowl is removed, don't rest the carb on the motor, as you may bend the floats (the two roundish black plastic peices that were inside the float bowl). Right in the center of the carb body (below and between the floats) you'll see a hex-shaped brass thing: that's the main jet. Sitting around the main jet is a white plastic splash sheild, slide it off the main and note how part of it goes into the carb body; that passage is where the pilot jet sits. Use a 6mm nut driver to remove the main jet, be careful not to lose the brass washer under it. Now install the new main jet with the old washer, being careful not to overtighten the main jet. Slide the shield back over the main and into the pilot jet passage. Put the float bowl back on, tighten the four screws, make sure there's no dirt in the carb or boots, and put the carb back in the boots just opposite of how you took it out. Now do the other carb the same way, replace the choke tube and connect the fuel and overflow hoses, turn on the fuel and make sure fuel doesn't flow straight out the overflow hoses. If it does, the float valve is stuck open, just tap on the float bowls with a large screwdriver and they should close.
Q#21:I need to rejet
pilots, how do I do it?
A#21:Follow the instructions above (A#20), and find the pilot jet instead of removing the main jet. Use a small flathead screwdriver to remove the pilot jet and install the new one. Make sure that the small pilot jet passage isn't clogged, it only takes a speck of dirt to block the pilot jet. Also make sure you have the pilot jets specific to Banshees, a standard Mikuni pilot jet is longer and will not fit (see below for more info).
Q#22:I need to adjust my needle clip
change my needles, how do I do it?
A#22:Start by making sure your Banshee is clean, specifically around the carb tops. If you have stock TORS carb caps, remove the side retaining screw and unscrew the carb top off the carb body; if you have aftermarket Mikuni carb caps, simply unscrew them (do one carb at a time if possible to prevent reversing the carb slides, if you are unsure which slide goes into which carb, look at the bottom of the slide; the cutout or bevel at the base of the slide should face the airbox). Once the top is loose, lift it straight up and the carb slide below the cap will come out of the carb body. With one hand, hold the carb cap and bunch up the spring, holding the slide in the other hand. When you have the spring compressed, look at the top of the slide and notice how the gold-colored cable retainer sits. Now turn the slide upside down and the cable retainer will fall out. You can now push the cable from the carb cap into the slide slightly and move it to one side, freeing the cable from the slide. Let the spring decompress and leave the carb cap resting on the pipe or frame rail. Use a small phillips-head screwdriver to remove the two screws on the top inside of the slide and remove the screws and retaining plate, then push the needle up and out of the slide. To change the needle clip position, look at what clip position it is in, remove the e-clip with a pair of needlenose pliers (you might want to do this part over a clean bench so you don't lose the clip), and then place the clip in the desired slot. Remember that moving the clip up towards the top or blunt end will make it sit lower in the slide, so the fuel flowing past the taper of the needle will decrease; so the 1/4 to 3/4 throttle jetting will be leaner. Conversely, moving the clip down towards the bottom or pointy end of the needle will make it sit higher in the slide, so fuel flowing past the taper of the needle will increase; making the jetting richer from ¼ to ¾ throttle. After setting the clip position, drop the needle into the slide, then drop the retainer in the slide. Make sure the hole in the top of the slide lines up with a notch on the retainer, this is to allow air to move in and out from the area above the slide as it moves, if not lined up you could have problems with the throttle sticking. Once the retainer screws are tight, bunch up the spring in one hand again, hang the slide on the throttle cable, and drop the gold cable retainer in place inside the slide. This is probably the hardest part, and a third hand here doesn’t hurt. With the cable retainer in place, let the spring decompress into the slide. Now position the slide into the carb body, making sure the cutout faces the airbox, and lower the cap and slide together into the carb. Make sure the slide doesn’t hang on the guide pin, rotate the slide if necessary so the groove on the slide lines up with the pin inside the carb. You should feel no resistance as you drop the carb cap and slide into place. Also make sure the tip of the needle goes into the needle seat hole and doesn’t hang up there. Carefully thread the carb cap on the carb body, the threads are very fine and the aluminum won’t survive cross-threading. Once tight, do the other carb the same way. When both carbs are done, be sure to check the carb sync. Any time the carb caps are off there’s a possibility that they won’t be tightened to the exact same location, so chances are the sync will be off.
Q#23:I need to adjust my idle speed, how
do I do
A#23:If you have the stock TORS system, turn the knobs on the upper rear of each carb top equally to adjust the idle speed. If you have aftermarket Mikuni carb caps and idle screws on the outside of each carb, loosen the locknut on each idle screw and turn the screws equally in or out, then retighten the locknut. On a side note, if you installed the idle screws and they do not raise the idle speed when turned all the way in, you either need to file more material off the carb body where the locknut seats, or make sure the slides aren’t reversed; on the left of the left carb slide and the right of the right carb slide is a small ramp that hits the tip of the idle screw, if the slides are reversed the idle screw will not raise the slides, and therefore change the idle speed (and it will run like crap if at all).
Q#24:I need to sync my carbs,
how do I do it?
A#24:There are several methods to tell which carb to adjust; one is to use an airflow meter at each carb, another is to use a tool that measures vacuum (Motion-Pro sells these for multiple-cylinder motors), and last is to do it by sight. Whichever method you use, the actual adjustment is the same; for stock TORS-equipped carbs, adjust the knob on the upper rear of the left carb top; for aftermarket Mikuni carb tops, loosen the locknut on the left carb top and adjust the center hex-shaped part that the throttle cable goes into. If adjusting the left carb will not sync the carbs, you may need to set the adjuster in the center of it’s range and try adjusting the right carb. To check the carb sync by sight, remove the air filter(s) and look into the carb throats, watch the very bottom of the carb slides as you gently push the throttle. If one slide moves before the other, you need to adjust the left carb until they both move from zero throttle at the same instant. Once set, you should be able to pin the throttle and release it, and hear both carbs “click” shut in unison; if you hear two clicks they are still not in sync (or you possibly have a problem with either the slides sticking or the slide return spring).
Q#25:My throttle stuck wide open and I
injured myself/my riding buddy/a small animal, what the hell?
A#25:Banshees are notorious for sticking throttles, 99% of the time it’s right after moisture hits the carbs; hitting a water puddle, getting a little too happy with the pressure washer, or playing submarine. This may be one of the reasons Yamaha opted to install the TORS system, and so far a definitive solution hasn’t been found. If water was indeed the culprit, start by checking your carb top gaskets (see Q#22 & 24), and make sure the tops are secure (don’t forget to sync the carbs, Q#24, whenever you have the tops off). Next try using either silicone or waterproof grease on the throttle cable where it enters the carb tops. If water is NOT the problem, something is probably preventing one carb slide to drop. Start by removing the air filter to see which carb slide is hung up. One possibility is that a piece of dirt from the fuel tank has lodged in the needle seat and won’t let the needle pass (see Q#27). Another possibility is that the guide pressed into the inside of one carb has backed out, allowing the slide to turn and hang. If this is the case, find the guide (located on the right side of the left carb body, left side of the right carb body), make sure it is placed with the tip vertical so the groove on the carb slide will fit on it, and use a hammer & punch on the outside of the carb body to secure the guide.
Q#26:When I turn the fuel petcock “on”,
out the overflow hoses, why?
A#26:Either you need to adjust the float height, or clean the float needle. If you’ve just had the carbs apart or they have been sitting dry for a while, first see if the floats can be unstuck by tapping on the carb bowls with a screwdriver handle. If that doesn’t work you’ll need to remove the carb and check the float height and float needle. Remove one carb top (see Q#22) and set the top assembly aside, then remove the carb body (see Q#20). Set the carb body upside-down on a bench, then remove the float bowl and gasket. Locate the pin that the floats pivot on, and use a small punch to drive the pin to one side (one end is flattened like a nail head so you can only drive it out one direction). Remove the pin and lift the floats straight up, hanging in the center of the metal piece connecting the plastic floats is the float needle. Slide the float needle off the float bracket, and look at the black rubber tip. If there is a speck of dirt on the tip of the float needle or the seat where the float needle sits, it will prevent the float needle from seating and let fuel overfill the bowl, and then run out the overflow hoses (if there is debris, see Q#27). If the tip of the float needle and the seat is clean, check the float height. Hang the float needle back on the float bracket and set the assembly back in place so that the float needle drops into it’s seat and the float bracket pivot holes line up with the holes in the carb body, then reinstall the pivot pin (tap the flattened end lightly to seat the pin). With the carb still sitting upside-down on the bench, measure the distance from the carb body gasket surface (WITHOUT the gasket in place) to the highest point on the black plastic floats (without putting any pressure on the floats). This measurement should be between 20mm and 22mm. If adjustment is necessary, gently bend the metal float bracket on each float to reach the right height. A simple tool can be made to measure the float height out of cardboard, simply cut L-shaped pieces that measure 20mm, 21mm, and 22mm from the top of the L to the top of the leg of the L:
After setting the float height, reinstall the float bowl gasket, float bowl, and carb body. Install the carb slide and top, and if necessary do the other carb. Don’t forget to install the choke tube between carbs, check the carb sync, and if fuel runs out the overflow hoses when you turn the fuel petcock “on”, tap on the float bowls again to see if you can unstuck the floats.
Q#27:I removed my carbs
and found dirt/debris/filth in the float bowl, why?
A#27:If there’s dirt in the carb bowls, chances are it got there through the fuel system and not through the air filter. This can lead to fuel running out the overflow hoses if dirt gets in the float needle (see Q#26) or worse, a sticking throttle (see Q#25). A common cause is that the strainers inside the fuel tank have fallen off the fuel petcock, allowing whatever sediment lurking in the bottom of your fuel tank to go straight into the carb. To check the strainers, turn the fuel petcock “off”, disconnect the fuel line where it Tees between both carbs, direct the hose into a fuel jug, and turn the fuel petcock “on” until the fuel tank is dry. Remove the two large Phillips-head screws that secure the fuel petcock to the bottom of the fuel tank (depending on what pipes you have you may have to remove the front plastic and fuel tank to get to it). There should be two white plastic strainers attached to the fuel petcock, if one or both has fallen off get them out of the fuel tank and put them back in the petcock with a little super glue. If the strainers are missing or torn, either replace them or add an in-line fuel filter on the fuel hose between the fuel petcock and the Tee. The in-line fuel filter will catch anything that the strainers miss and should not have any affect on fuel delivery (get a clear one so you can see when it gets stopped up and you need to replace it, having a spare in the toolbox is a good idea too).
Q#28:I removed my carbs
and found dirt/debris/filth on the slides or inside the boots, why?
A#28:The three most common causes of dirt entering the carbs are; the stock air filter not held on by the airbox lid correctly, a torn air filter, or a cracked airbox boot. The stock air filter mounting system is simply crappy, sure you can remove the air filter with no tools, but how often do you need to do that? And how many of us carry a spare clean & oiled air filter with us? Some people have no trouble getting the airbox lid on right so that it hold the air filter (the easiest way is to set the lid on one side and lower the other side in place, watching to make sure the lip on the lid catches tha air filter cage), others never get it right (those are the guys that do a topend after every ride). The best solution is to replace the entire air filter and/or mounting plate with an aftermarket product that will eliminate any possibility of the air filter not sealing correctly. Pro Design and UMI Racing offer aluminum adapter plates that permanently mount to the front of the airbox, and allow a foam or K&N air filter to be securely clamped in place. Toomey offers a 2 into 1 system that eliminates the entire airbox, and single foam or K&N filters can be mounted directly to the carbs. Anything is an improvement on the stock setup, just be sure to choose the right setup for your needs (opinions vary but in general you want to keep the airbox and possibly the airbox lid if you ride in wet or muddy conditions, a foam filter for extremely dusty conditions, and K&N(s) with Outerwear(s) for sand). Whenever you clean your air filter look for any holes or seams coming apart that could allow dirt to pass and replace or upgrade the filter if necessary. Finally, if the air filter is OK make sure there are no cracks in the airbox boots.
Q#29:What is the TORS?
A#29:TORS is the Throttle OverRide System found on stock Banshees. It consists of the large boxy carb tops, a switch on the thumb throttle housing, a switch on the parking brake perch, and a control box mounted to the frame rail above the left cylinder. The function of the TORS is to limit engine RPM if the parking brake is engaged, or if the throttle is released and the carb slides don’t shut (see Q#25). If the switch at the parking brake senses that the parking brake is engaged, it tells the carb tops not to lift the carb slides. Similarly, if the switch at the thumb throttle senses that the thumb throttle has been released, the carb tops won’t lift the carb slides. The problem with the system is that often the switch on the parking brake perch will fail to sense that the parking brake is not engaged, and will then limit RPM (the motor won’t rev past idle); adjusting the switch is the first solution, eliminating the TORS is a better one. Other drawbacks to the TORS is that the carb tops are huge and makes jetting more time consuming, the entire system is one more thing that can (and usually will) fail, and the system adds unnecessary weight. Eliminating the TORS is well worth the effort.
Q#30:How do I eliminate the TORS?
A#30:Several companies sell TORS elimination kits (Toomey, Vito’s, etc.) that include aftermarket Mikuni carb tops, throttle cable, and an idle screw kit. The throttle cable and carb tops are a simple matter of removing the old and installing the new (be careful with the carb top threads and remember to check the carb sync, see Q#22). The idle screw kit requires removing the carbs, drilling a hole (on the left side of the left carb and on the right side of the right carb), tapping the hole, filing the casting flat, and installing the screws. Drilling the hole is simple, just place a small piece of wood inside the carb to prevent the tip of the drill bit from dinging the opposite side of the carb when it goes through. Tapping the threads is also easily done, however be careful to use a good quality tapping fluid and run the tap in slowly; half turn in, quarter turn out, etc. Breaking the tap off is an exceedingly bad idea. Make sure to file off enough material at the end of the casting, about ¼”, so that the idle screw can raise the carb slide. Once installed, you can remove control box, the parking brake switch and thumb throttle switch (follow the wires to a connector and either disconnect it or cut the wires). Be sure to clean the carbs thoroughly and use compressed air to blow out any drill filings, and check the throttle cable free play. More details on installing the kit can be found at www.toomey.com in the tech section.
Q#31:What’s the choke tube and what does it do?
A#31:The choke tube is a small hose that sits between the two carbs, on the opposite side of the choke knob on the left carb to the left side of the right carb. The tube allows fuel drawn from the choke circuit on the left carb to richen both carbs when the choke is “on”. If the choke tube is removed and the motor run, it will run like crap, if at all.
Q#32:What’s the choke trick?
A#32:The choke trick is an easy way to tell if you are rich or lean on one or more jetting circuit. Since the choke richens the mixture, you can use the choke to quickly find out if you need to richen or lean out your jetting: with the motor fully warmed up, pop the choke out to the first notch (half choke) and ride it; if it runs better with the choke then you know you need to go richer on your jetting; if worse you should be able to safely lean out your jetting. As with any other jetting issue, make sure you rule out any other possibilities before changing the jetting (electrical, mechanical, air filter, etc.).
Q#33:What’s a plug chop?
A#33:A plug chop is one way to verify your main jet jetting. To do a plug chop, make sure the air filter is clean, warm up the motor, shut it off and install two new spark plugs. Start the motor and pin the throttle, running through all 6 gears. When you wind out the top of 6th gear, hit the kill switch and pull in the clutch, keeping the throttle pinned. Remove the spark plugs (put in the old ones to get home if necessary) and put one in a vise. Using a hacksaw, cut the threads away from the center electrode with one cut parallel to the electrode and one cut perpendicular to the base of the electrode, so you can see the very base of the center electrode. If your main jets are spot on, you will see a 2mm tall chocolate-brown colored ring at the base of the electrode. If the ring is taller than 2mm or darker than a Hershey bar, you’re rich on the mains. If the ring is smaller than 2mm or lighter, or nonexistent, you’re lean on the mains. If both plugs aren’t almost identical, one cylinder may be richer or leaner than the other (if leaner then an air leak is likely on that cylinder). Keep in mind that doing a plug chop is best used as a way to verify your mains, since you will be wound out in 6th gear there’s a potential for damage if you are way too rich or lean (see Q#12). While it’ll cost you a couple bucks for new plugs, the plug chop, if done correctly, I believe is the single best way to find out if your mains are dialed in for your current mods, temperature, and elevation.
Q#34:What’s an air leak and why is it so bad?
A#34:An air leak is any place that air can get into your motor besides the right way: through the air filter, through the carbs, through the reed cage, and into the cylinder. An air leak can develop between the air filter and airbox, between the airbox and airbox boot, between the airbox boot and the carbs, at the carb tops, between the carbs and the reed cage, on the reed cage boots where the balance tube sits, at the reed cage gaskets, at the cylinder base gaskets, and at the crank seals. Anywhere that air can get in will cause problems, if it gets in before the carb then there’s a potential for dirt to enter the motor, causing rapid ring wear and ultimately piston failure. Air getting in between the carb and cylinder or through a crank seal will cause a lean condition on that cylinder, which also will cause rapid damage due to overheating. Beware of any signs of being lean (see Q#8), especially if only on one cylinder, and immediately check for an air leak before it’s too late. To check for an air leak, start the motor and let it idle, then spray ether around the carb boots, tops, reed cages, and cylinder bases; if the idle goes up you’ve found the leak. If the left cylinder has an air leak, it could be the crank seal (since the left crank seal is between the left crankcase and the flywheel, it seals air out), you need to perform a leak-down test to find out for sure. While the right crank seal can also cause an air leak, typically it will suck transmission oil and foul the right plug before it can drain the tranny and start sucking air. For information on doing a leak-down test see www.duncanracing.com . As a side note, boost bottles sometimes cause cracks and subsequently air leaks on the reed cage boots, the extra weight of the boost bottle vibrating may contribute to accelerated boot failure.
Q#35:OK, I need to rejet
my mains, pilots, and needles, what do I do first?
A#35:Starting with a rough idea of where you should be at on the jet sizes and needle clip position (either by the manufacturer’s recommendations, the advice of others with similar mods taking temp & elevation into account, or by the recommendations below), install the mains, pilots, needles at the recommended clip position, and set airscrews 1.5 turns out. Make sure the air filter is clean and start the motor, using the choke if necessary, and let the motor warm up fully. Dial in the pilot/airscrew circuit first (see Q#10). Then dial in the main jets (see Q#12). Finally dial in the needle clip position (see Q#11). Following this procedure will 1) make sure you aren’t too lean or rich while warming it up (pilot/airscrew circuit), 2) make sure you aren’t too lean or rich at WOT, where it’s most critical, and 3) make sure you aren’t too lean or rich in the middle of the throttle range without confusing your main jet readings.
Q#36:Where the hell is the main jet/pilot
jet/needle/float etc. etc.??
A#36:Inside the carbs. By the way, the carbs are those silver things right between the motor and the air filter. OK, OK, how’s this:
Thanks to Meat for the pics!
For an exploded view of the carbs, take a look at the online microfiche available at www.yamahaoftroy.com.
Q#37:How do I read my spark plugs?
A#37:Aside from doing a plug chop (see Q#33), you can read your spark plugs to get an idea of your overall jetting (to see the base of the center electrode you'll still need to either cut the threads away or use an illuminated magnifying glass). You’ll need to ride for at least 30 minutes to get a reading, but once done you can find out about your overall jetting, ignition timing, and spark plug heat range. Be advised that it’s not a good idea to ride around when you know it’s way too lean or rich (see Q#7 & 8 for symptoms), and remember that unless the throttle is held at a constant position the jetting indications on the spark plug are an "overall" idea; one circuit can be rich and can mask a lean circuit. Thanks to Boonman for the detailed instructions!
Refer to the illustration following instructions;
1. You set your heat range from the ground strap (this is the piece closest to the piston)
2. You do all the plug readings for jetting from the base ring (the base ring is what the ground strap is welded to at the end of the threads)
3. You determine detonation and timing issues from the porcelain (the porcelain shows preignition/detonation, it will not accurately determine jetting / air/fuel
ratios) DO NOT BASE JETTING DECISIONS ON THE PORCELAIN COLOR AT THE TIP.
1. How to determining plug heat range:
The ground strap is your window to getting this right. If the "color" of the ground strap "changes" too-close to the ground strap's end, (the end opposite of the base ring), then the heat-range is "too-cold" (heat transfer is too quick to the base ring). If the "color" of the strap changes near where it is welded to the base-ring, then it means that the plug heat-range is "too-hot" (heat transfer to the base ring is to slow causing the deposits to be burned off the strap completely). The strap at this point could start working like a "glow-plug", probably resulting in pre-ignition and/or detonation. The properly set heat-range is when the "color" is at the half-way point on the strap.
The base ring "color" is very close to the color of the piston crown and is used to determine the jetting. You're looking for the soot color to be a nice light to medium brown, (color is always hard to describe) if the color doesn't go all the way around the base ring (at least one full thread turn on the plug) or the color is whitish it is way too lean. If the color goes all the way around, but there is a spotting of heavy dry soot on the top of the color, you are too rich.
3. Read the porcelain to determine detonation/preignition:
The first signs of detonation/preignition will be seen on the porcelain down in the plug, It shows up as tiny black or shiny specks of aluminum. Also look very close around the center electrode where the porcelain intersects, this will appear to be melting between the insulator and the electrode. Detonation is caused by the air/fuel mixture exploding rather then burning. This gives off a sound (a knock), this sound is the result of a shock wave, this wave disrupts the boundary layer of cooler gases that cover the internal parts of the combustion chamber. This causes a very rapid rise in pressure and temperature. The results are holes in the top or sides of the pistons, blown head gaskets, broken rods (all bad stuff), this can also shock the rings from their seal causing oil to form as little spots on the porcelain.
Q#38:What’s the deal with the airbox
A#38:The black rubber snorkel on the front of the airbox lid is intended to draw air a little higher than the airbox, in an attempt to lessen the amount of water that enters the airbox (and to a lesser extent, dust). However, the snorkel alone is quite restrictive. In most cases the snorkel can be removed without a dramatic increase in water intake, and will increase airflow enough to necessitate going one or two sizes larger on the mains (see Q#12). Keeping the snorkel in place after adding pipes will restrict airflow significantly, and you won’t see near as much hp gain with the snorkel on (same goes for the airbox lid, see Q#40). When doing mods such as aftermarket pipes and/or air filter, it’s best to remove the snorkel to allow your motor to breath efficiently. Removing the snorkel and rejetting to compensate on a completely stock machine will, in most cases, improve performance slightly, while not risking any damage (unless you’re riding through water above the seat, and in that case you’re pretty much asking for trouble anyway).
Q#39:What’s the deal with the airbox
A#39:Like the snorkel, the airbox lid protects the air filter from water & dust, and like the snorkel the airbox lid can pose an airflow restriction after a certain number of mods (like pipes and air filter). Unlike removing the snorkel, removing the airbox lid on a completely stock machine won’t have much affect (even after rejetting to compensate), and without the lid in place to retain the stock air filter, the filter will fall off allowing dirt to enter and subsequently damage your motor. In addition, running without the airbox lid on, when using an aftermarket air filter setup that doesn’t require the lid to secure the air filter, can allow water and mud to enter the airbox. If your riding conditions lean towards swampy, it may be a good idea to keep the airbox lid in place even after adding pipes and air filter, to keep the air filter from loading up and/or passing water. That said, if mud & water are not a concern, removing the airbox lid after adding an aftermarket air filter & adapter plate and pipes will allow the most airflow (short of a 2 into 1 or dual filters), and still offer some protection from the elements. Plus you can keep the lid and throw it on when you wash your Banshee to protect the air filter.
jetting dialed in perfect for my mods and
but the temperature ranges significantly during the day, what can I do?
A#40:EFI is the best solution, since it will automatically compensate for changes in air density; this is still prohibitively expensive though (at least in my opinion). Another option is a Dial-a-jet, which allows you to alter the jetting (by about one or two main jet sizes) with the turn of a dial (I don’t have firsthand experience so I can’t comment). Aside from rejetting the mains in the middle of the day (and possibly again in the evening), the only other alternative is to use the airbox lid. Say you have an aftermarket air filter setup; dial in the mains with the airbox lid on for the coldest point in the day; then as the air temperature increases, it will start to run rich (bogging at WOT, see Q#12); simply remove the airbox lid (which is about equal to one jet size on the mains) and voila, you’re stylin’. Depending on your specific mods, this may or may not work, but at least it’s an option (it would be a good idea to make sure you’re not lean when you take off the lid by reading the plugs, and don’t forget to replace the lid as the temperature drops, otherwise you run the risk of being lean).
Q#41:You said you’d
recommendations for different mods, what
A#41:First, realize that every Banshee is different, so these recommendations are only meant to get you in the ballpark for your jetting. Second, remember to add or subtract sizes for ANY of the below that apply (airbox lid, filter, temp, elevation, etc.). Third, if there’s any doubt about jet size, err on the side of rich to start with, and work your way leaner (see Q#12).
Assuming that your jetting is dialed in perfectly, add the following for each mod:
Remove snorkel:1-2 sizes larger on the mains, adjust airscrews
Remove airbox lid:1-2 sizes larger on the mains, adjust airscrews
Add foam air filter:0-2 sizes larger on the mains, adjust airscrews
Add K&N air filter:4-6 sizes larger on the mains, adjust airscrews, add one size on pilots if necessary
Add 2 into 1 Foam air filter OR dual carb-mounted foam filters (removing entire airbox, NOT in addition to removing snorkel and airbox lid above):2-4 sizes larger on mains, adjust airscrews, add one size on pilots if necessary
Add Dual K&N carb-mounted air filters (no airbox, NOT in addition to removing snorkel and airbox lid above):4-7 sizes larger on the mains, adjust airscrews, add one size on pilots if necessary
Add Outerwear:no change
Add TORS elimination kit:no change
Add Pipes & silencers (all except 2 into 1 pipes):8 sizes larger on the mains, 2 sizes larger on the pilots, adjust airscrews
Note:Some pipes, like CPI and other “drag” pipes, may need even larger mains, midrange pipes may only need one size larger on the pilots
Add 2 into 1 Pipe & silencer:4-5 sizes larger on the mains, 0-1 sizes larger on the pilots, adjust airscrews
Add Reeds, Aftermarket reed cage, or Ported reed cage:Move needle clip one position leaner, adjust airscrews, 0-2 sizes larger on the pilots
Add Degree key or Timing plate with advanced ignition timing:0-1 sizes larger on the mains, adjust airscrews
Switch coil wires (A lot of Banshees come from the factory with the orange positive wire on the “-“ terminal of the coil, and the black ground wire on the “+” terminal of the coil, switching the wires would put orange on “+” and black on “-“):0-1 sizes larger on the mains, adjust airscrews
Add Aftermarket ignition system:4-8 sizes larger on the mains, adjust airscrews
Add Coolhead with smaller domes or shave stock head:no change
(be advised that your octane requirements may change)
Re-ring pistons:no change
Forged pistons (stock crown, port timing and pin location):no change
Weld crank/rebuild crank:no change
Lighten flywheel:no change
Rewind stator:no change
Boost bottle/aftermarket intake manifold:no change
For every 1500-2000’ above sea level, add to above:1 size smaller on the mains, adjust airscrews
For every 1500-2000’ change in elevation after jetting is dialed in:1 size smaller on mains for higher elevation, 1 size smaller on mains for lower elevation, adjust airscrews
For 60-90 degrees F:no change to above
For every 20-30 degrees F colder than 60:1 size larger on the mains, adjust airscrews
For every 20-30 degrees F warmer than 90:1 size smaller on the mains, adjust airscrews
For every 20-30 degrees F temp change after jetting is dialed in:1 size larger on mains for colder temp, 1 size smaller on mains for warmer temp, adjust airscrews
Very low humidity to very high humidity:0-2 sizes smaller on mains, adjust airscrews
Very high humidity to very low humidity:0-2 sizes larger on mains, adjust airscrews
32:1 ratio:no change to above
Higher ratio (40:1, 50:1, etc.):0-2 sizes smaller on mains, adjust airscrews
Lower ratio (20:1, 24:1, etc.):0-2 sizes larger on mains, adjust airscrews
Your Banshee is bone stock, 32:1 premix, you’re at sea level and it’s 60-80 degrees. You add a K&N air filter, remove the airbox snorkel, remove the airbox lid, and mount Pro Circuit pipes & silencers. IF your current jetting is 25 pilot, 200 mains, start by going up to 340 main jets (14 sizes larger; 8 for pipes, 4 for K&N, 1 for snorkel, 1 for airbox lid), 30 pilots (2 sizes larger for the pipes), leave the needle clip in the stock location, and start with the airscrews 1.5 turns out. If you got some reeds at the same time, everything would be the same except you’d start with the needle one clip position leaner than stock.
recommendations for porting in the mods
A#42:Porting is always the wildcard as far as jetting is concerned. With so many different variables there’s no way to even come close. Suffice it to say, always start on the rich side and work your way down (see Q#12), this goes for pistons that alter the port timing as well. However, a reputable porting shop should be able to get you real close on your jetting, if they can’t, don’t give them your cylinders…
Q#43:I followed all your directions above and now my Banshee won’t run, my wife left me, my dog bit my leg, a
asteroid is on a collision course for earth, blah blah
A#43:So you want a disclaimer? Allright: the thoughts and opinions expressed on this page are solely those of the author, who takes no responsibility whatsoever for the results of any actions that may injure or kill the planet’s inhabitants if done at home or in the parking lot of a 7-11, and who by the way is NOT laying on a beach in the Carribean sipping exotic elixirs and tapping the asses of scantily clad beach bimbos right now because he didn’t make a damn cent off of trying to help fellow enthusiasts by composing this document. If you want to piss and moan, file litigation, protest in front of the White House, whatever…tough shit, I’m goin’ riding.
One more big thanks to all the awesome members of the www.bansheehq.com forums for all
and input, I can't name you all but you know who you are, I couldn't
it without you!!
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