Banshee38 Posted March 23, 2009 Report Posted March 23, 2009 I have fmf exhaust system with a K&N and a boost bottle (if the boost bottle even really matters). I would like to find out what my quad should be jetted at because before i get into the powerband it bogs alot and want to know if the jetting has anything to do with it. Its currently jetted at 240. Thanks Quote
4u2nv Posted March 23, 2009 Report Posted March 23, 2009 what size pilot do you have ? Is it ported or any engine mods done ? Boost bottle is there for air exspansion to and for engine. Quote
Banshee38 Posted March 23, 2009 Author Report Posted March 23, 2009 what size pilot do you have ? Is it ported or any engine mods done ? Boost bottle is there for air exspansion to and for engine. The pilot size is 25. No there is nothing done to engine. Quote
GrMeyer Posted March 24, 2009 Report Posted March 24, 2009 we need to know what your elevation is and is it a K&N with lid/ without lid. K&N pods. I have fatties running pods with no motor running 290 main jet and 25 pilots. But if it is a bog before the power band then it is more then likely airscrew 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 idle, OR 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 half throttle... 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. Quote
Banshee38 Posted March 24, 2009 Author Report Posted March 24, 2009 we need to know what your elevation is and is it a K&N with lid/ without lid. K&N pods. I have fatties running pods with no motor running 290 main jet and 25 pilots. But if it is a bog before the power band then it is more then likely airscrew 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 idle, OR 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 half throttle... 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. Thanks for that info. I just went to fmfracing.com and it gave me all the info i needed about jetting it. Quote
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