CRF450 Help!!! or just a good mechanics help!

[416exmx]

I bought a whole CRF450 bike to use the motor in a quad frame... when I bought the bike it ran AWESOME.... after I got it in the quad frame it just runs like crap. It cuts out bad on bottom to mid-range and shoots flames when revved up. I have a different boot from the motor to carb to help align carb. I thought that was my problem but after putting the stock one back on that is not it. We have jetted and jetted and jetted... I have replaced carbs, coil, cdi and stuff like that. Still no good. I just put a new stator on because the pickup part on it was melted and shorting out. That still didn’t fix it. I don’t know what else the problem could be... the motor has a new topend, valves, and cam chain. It should be in time because it ran good in the bike (motor was rebuilt while in the bike chassis)... it has a CRF FMF head pipe and 400ex Yoshi silencer.... maybe not enough back pressure or maybe too much????? Also would the tilt of the motor (front to back) have anything else to do with this?????? I can’t figure it out for anything. Like I said it runs bad and just cuts out on bottom to mid-range and just shoots flames when revved up. It idles fine and does ok when flying through the gears on top-end.

[INFANTRY RACING]

when it running spray some starting fuild on your intake area to check for air leaks. it sounds like a lean condition.

[416exmx]

i put a new wiring harness, spark plug, and cleaned all the grounds... it runs much better but still shoots flames out of the exhaust and pops... now it could be a jetting issue

any other ideas????

[NacsRacing400]

Its lean, try going up on the pilot a few sizes up and see if it clears up the backfireing.

[deansfastway]

You might want to check to see if the throttle slide is upside down . When the dark metal throttle slide insert is upside down the FCR carb wont work properly and cause incopncievable jetting situations . and its very easy to get it confused . Poor low speed operation surging and popping and stalling . Ive seen it one more than a few occasions on CRFs and YZFs. Good Luck

[deansfastway]

might also want to check the valve clearances and the accel pump function, hot start sticking and function