Running on one cylinder?

[justwall]

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.

[sick421]

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

[justwall]

What psi should I be shooting for?

[toytech]

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.

[justwall]

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.

[kedge82]

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

[BeeCanBanshee]

I had a one cyl fire problem twice. First time was bad coil and second time was a bad float valve in the carb.

[HiRoller]

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.

[SOUTHTHIRTY]

float valve? the float needle with the little rubber tip--- is this what your talking about?

[BeeCanBanshee]

Yup