breaking up on top

[jbones]

i have a 280 main jet needle clip in stock postion 3/8 reed spacer boost bottle toomy pipes stock air box with cover off k&n filter stock pilot jet but it breaks up on top end full throttle. it will run at full throttle with choke a little open but wont idle . i turned the air mix screws in from 2 1/2 to 1/2 and it ran better at full throttle with choke off it seems like it needs to get more fuel or run richer?

Edited September 2, 2008 by jbones

[BenBB]

Have you tried going up on the mains at all? Sounds like it's just lean on the mains, if it idles ok with the stock pilots now I'd leave the pilots alone and just try 290 or 300 mains and see how it runs (mains are primarily responsible for mixture between about 3/4 and full throttle, needle about 1/4 to 3/4 throttle, and pilots are idle to about 1/8 throttle); when you use the choke trick it makes it rich all the way through so if it ran better at WOT and not at idle that tells you to go richer just on the mains, once you get those dialed in use the airscrews to fine tune idle and off-idle response. Good luck.