oih8u2 Posted March 23, 2010 Report Share Posted March 23, 2010 Just like the title says, I'm at 500 on the main jet with stock 26mm carbs. This is what I've done to the quad: HotRods 4mil long rod crank with base spacer ProCircuit platinum pipes with 304 silencers Boyesen reeds no porting but smoothing of the exhaust port bored .040 over with Wiseco 795 pistons K&N pods with prefilters now here is where my stock mikuni carbs are currently setup to: main: 500 pilot: 35 air screw: 1.5 turns jet needle: dynojets dno304 4th clip from the top (out of 6) needle jet:O-8 valve seat size: 2.8 my elevation is 800 feet currently it is 40F, but I'd like to have it setup for 80F-90F. So far it starts great and idles fine. I have acceleration through 1-4, 5th lags and 6th just slows down. What should I do??? At what point does the valve seat and fuel petcock act like a main jet? Will going to a larger carb really cure my problems? Does changing the spark plug heat range make that much difference? I have read the "Banshee jetting FAQ" from this site many times and have a copy of it in my toolbox. My riding style is mostly trails and gravel pits. Ask any questions if I have missed any details that you's need to recommend for jetting. I'd like to hear your thoughts on this one. Quote Link to comment Share on other sites More sharing options...
GNR101 Posted March 23, 2010 Report Share Posted March 23, 2010 Just like the title says, I'm at 500 on the main jet with stock 26mm carbs. This is what I've done to the quad: HotRods 4mil long rod crank with base spacer ProCircuit platinum pipes with 304 silencers Boyesen reeds no porting but smoothing of the exhaust port bored .040 over with Wiseco 795 pistons K&N pods with prefilters now here is where my stock mikuni carbs are currently setup to: main: 500 pilot: 35 air screw: 1.5 turns jet needle: dynojets dno304 4th clip from the top (out of 6) needle jet:O-8 valve seat size: 2.8 my elevation is 800 feet currently it is 40F, but I'd like to have it setup for 80F-90F. So far it starts great and idles fine. I have acceleration through 1-4, 5th lags and 6th just slows down. What should I do??? At what point does the valve seat and fuel petcock act like a main jet? Will going to a larger carb really cure my problems? Does changing the spark plug heat range make that much difference? I have read the "Banshee jetting FAQ" from this site many times and have a copy of it in my toolbox. My riding style is mostly trails and gravel pits. Ask any questions if I have missed any details that you's need to recommend for jetting. I'd like to hear your thoughts on this one. 500 mains?? what u running 5bar into that motor? i would say 500s are a tad big... do a plug chop with those mains... i bet ull have2 drop them a mile Quote Link to comment Share on other sites More sharing options...
SAVAGE420 Posted March 23, 2010 Report Share Posted March 23, 2010 You sure have 500 mains in? And if you did ..... You would not even need a 500 main with your set up if you were 5000' BELOW sea level. You should be in the mid 300's on your mains and a 27.5-30 pilot MAX. You sure you have no air leak your compensating for? Did you pressure test the motor to see? You can always go through this and find the same exact setup and conditions. http://bansheehq.com/forums/index.php?showtopic=99361 Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted March 23, 2010 Report Share Posted March 23, 2010 I had some customer call me tonight, he has 480 main jets in a set of TM 28mm carbs. He just put a top end on and didn't even check the squish. I am almost 100% positive he has excessive squish, and is chasing a motor problem and not a jetting problem. 500 mains in stock carbs is fucking ridiculous. You need to be looking elsewhere for the problem, its not the main jets. Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted March 23, 2010 Report Share Posted March 23, 2010 x2 Quote Link to comment Share on other sites More sharing options...
oih8u2 Posted March 23, 2010 Author Report Share Posted March 23, 2010 I have had the motor pressure checked. It held 6psi for 30 minutes. There are no holes or tears in the carb boots. With anything less than a 35 pilot it stubbles and starts to backfire. although with the dynojet needle and a 420 main, it had a smoother transition into the powerband with a hiccup, but still fall flat in higher gears. pugs are coming out black upto just before mid throttle and then in the high rpm's the plugs are faintly brown with a hint of grey. top of the pistons are mint, exhaust side of the piston is mint. even with the stock needle, i couldn't go below a 340 main for it would be backfiring and missing. and again good idle, poor midrange, and a top end that would fall flat in the higher gears. Quote Link to comment Share on other sites More sharing options...
Wheelie Ripper Posted March 23, 2010 Report Share Posted March 23, 2010 I have a similar set up, 4mm with spacer, .040 over with 795 pistons, pt mid pipes, foam filter with no air box lid, 20cc domes +4 timing and stock carbs. Runnings 350 mains and 30 pilots and it runs perfect, 360 it bogged wide open, went to 350's and it runs cherry. Try soaking the carbs and make sure both are getting enough fuel because something does not sound right Quote Link to comment Share on other sites More sharing options...
firebanshee Posted March 24, 2010 Report Share Posted March 24, 2010 Get rid of the spacer plate, they throw off port timings. There is NO WAY you need that big of jets unless you are running methanol. You need to figure out what is wrong with your set up. Quote Link to comment Share on other sites More sharing options...
AKheathen Posted March 25, 2010 Report Share Posted March 25, 2010 ok, i can see that porting, squish and airleaks can throw your jetting off, but i do see one other thing it could possibly be. you say it has 0-8 needle jet. i don't remember what numbers are on the stockker, but i uses an emultion tube in there with a bunch of tiny holes in the side. it doesn't need to be restricted that much by an airjet, so they use a 1.4 airjet, which is extreemely huge as far as air jets go- almost the same size as the choke jet. it will allow allot of air to bypass the main jet, since it's about the same size. Quote Link to comment Share on other sites More sharing options...
rascal Posted March 25, 2010 Report Share Posted March 25, 2010 500 mains?? what u running 5bar into that motor? i would say 500s are a tad big... do a plug chop with those mains... i bet ull have2 drop them a mile try a 360 or 370 main. it will run great Quote Link to comment Share on other sites More sharing options...
Snopczynski Posted March 27, 2010 Report Share Posted March 27, 2010 UPDATE: that guy brought his bike to me that had the 480 mains in it. I found a bad plug cap, he was running those funny little spark plugs, his stator was heavily rusting, and his flywheeel magnets are all rounded off and chewed up. Told him to fix that stuff, and let me know what happens. So far I haven't heard from him. Quote Link to comment Share on other sites More sharing options...
bigborebanshee Posted March 27, 2010 Report Share Posted March 27, 2010 500 mains in stock carbs is fucking ridiculous. You need to be looking elsewhere for the problem, its not the main jets. Could you imagine the trying to ride that think at the dunes.Probably needs the 4mill just to lug the extra 5 gallon gas can on his 6 pack rack..LOL Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted March 27, 2010 Report Share Posted March 27, 2010 I tune alot of bikes and everyone is diffrent.Sometimes you can reach a piont where its acting like its getting better but it gives you a false sense of seat of the pants reaction.I have had bikes pull big jets clean up top but infact ended up much leaner in the end.As stated by snop electrical plays a big factor in jetting,if everything is not rite you chase your tail.You must go by the plugs!You need to do a plug chop on a fresh set of plugs in a warm motor and establish a main size first be prepared to run through a few sets.If it doesnt pull wide open 6th gear for 5 sec drop jets till it does,dont worry what its doing in between just full Quote Link to comment Share on other sites More sharing options...
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