justwall Posted July 9, 2013 Report Share Posted July 9, 2013 I just picked up a banshee off of a seller and took it for a rip today. Upon anywhere between 0-3/4 throttle right up until powerband it bogs out unless I keep it in the band. Played around with it a bit to try and do some diagnostics and test plugs and I'm stumped. I have read a lot of these forums and I'm trying to narrow it down. I check and changed plugs and nothing. The right cylinder is running perfect with a mocha brown plug and the left cylinder looks like a brand new plug when pulled. I changed the cable a rounds to rule out and electrical problem and both plugs are sparking. I then pulled the carb apart to make sure they weren't all gunked up but clean as a whistle. Then performed a compression test on both cylinders and they both came in the same at 120psi. I am stumped. Could it be bad reeds any ideas? Here are what's in the banshee. Yamaha banshee 421 cheetah 421 jug set 4 mill stroker crankshaft adjustable timing plate Yamaha R6 clutch with upgraded springs shearer in frame drag pipes full system k and n bullet filters w/ outerwears fast racing high compression heads 20 cc domes 380main jet plus 1 front sprocket Any ideas would help as I've been out of the shee for a good couple years. Quote Link to comment Share on other sites More sharing options...
sick421 Posted July 9, 2013 Report Share Posted July 9, 2013 120 psi is junk for 20cc domes on a 421 cub, i would look into a top end rebuild. Another thing that can cause a 1 cylinder fire is broken reeds Quote Link to comment Share on other sites More sharing options...
justwall Posted July 9, 2013 Author Report Share Posted July 9, 2013 What psi should I be shooting for? Quote Link to comment Share on other sites More sharing options...
toytech Posted July 9, 2013 Report Share Posted July 9, 2013 our 421 with 21cc domes has 175 comp. you have low comp. you should do a leak down, sounds like an airleak on left side. Quote Link to comment Share on other sites More sharing options...
justwall Posted July 9, 2013 Author Report Share Posted July 9, 2013 I pulled the carb apart and cleaned now both cylinder are firing but still get bog. I noticed when I pulled it he had put a 380 main and a 27.5 pilot. Isn't the pilot too small for the amount of performance parts on it. It runs fine if you keep it in the high rpms but bogs from about 1/4 to 3/4 throttle. Quote Link to comment Share on other sites More sharing options...
kedge82 Posted July 13, 2013 Report Share Posted July 13, 2013 1/4 to 3/4 would be your needle clip settings bogging means rich so raise your needle clip one and see how shee runs Quote Link to comment Share on other sites More sharing options...
BeeCanBanshee Posted July 17, 2013 Report Share Posted July 17, 2013 I had a one cyl fire problem twice. First time was bad coil and second time was a bad float valve in the carb. Quote Link to comment Share on other sites More sharing options...
HiRoller Posted July 18, 2013 Report Share Posted July 18, 2013 I had a one cyl fire problem twice. First time was bad coil and second time was a bad float valve in the carb. I just had the same thing and it was the float valve. From what I've read they need to be replaced every 5 years or so. Quote Link to comment Share on other sites More sharing options...
SOUTHTHIRTY Posted July 18, 2013 Report Share Posted July 18, 2013 float valve? the float needle with the little rubber tip--- is this what your talking about? Quote Link to comment Share on other sites More sharing options...
BeeCanBanshee Posted July 18, 2013 Report Share Posted July 18, 2013 Yup Quote Link to comment Share on other sites More sharing options...
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