2000 trx 350fm. Started with difficult starting and running poorly. Given the age of the machine I decided to give it a bit of an overhaul. I rebuilt carb, and figured I’d check top end. In process of doing so, several of the 25 year old bolts and nuts didn’t make it. (South Louisiana environment) Ended up replacing head and cylinder. New valves and rings. Exhaust pipes were rusted out. Replaced with good used pipe and muffler. Set valve clearances to 0.005 each. Compression with WOT was 80 psi. On startup, would have random shut off. Checked plug and noted 2 cracks in ceramic. Replaced with new. Runs better and no more random shut off. What I have now is a rough idle (which I have to keep a little on the high side to stay running) and a backfire with throttle release. No change from factory carb air screw settings. (2 turns out if I remember right). I think a little tweaking will get it spot on. I’m just not exactly sure which direction to go in. Thoughts?

 

Running a little lean I would rotate counter clockwise to open setting

 

Was leaning (pun intended) that way. After running and riding for a bit more today, I pulled the plug and it was almost white. Ran like a brand new 350 while riding btw. Thanks. Going pull the carb.

 

Tried going out from 2 turns by 1/4 turns up to 2 3/4 turns. Very slight improvement at 2 1/4 turns. Beyond that, no improvement. Not sure what else to try. Do I need to re-jet carb? Can’t see why that would need to be done because everything is stock, but idk. Leak down test? Other suggestions?

 

Still have blockage in slow jet or curcuit, air leak at mount does it run better when apply choke? Spray wd 40 around the air cutoff value when engine is at idle if engine loads up an dies the plastic cut off value has crack or o ring missing or vaccum line there is cracked or installed wrong location.im just guessing after reading what you have already done.

 

Pulled carb and went completely through it again. (everything perfect). Checked boots on both end of carb for cracks and they looked good. Reinstalled carb. No change. Took it down the road and noted that it’s breaking up bad at full throttle. 🤷🏻‍♂️

 

Does atv have factory air box and air filter and snorkle? Is engine noisey? cam chain rattle?

 

Factory airbox and filter. Oiled and installed new filter last summer. Probably less than 4 hours on it. Ran it for about a minute without airbox attached while trying to diagnose. Didn’t make much difference. No snorkel. Everything is stock on it.

 

No snorkel? i meant factory snorkel.If you can ride without seat an use fingers to regulate air flow coming through snorkel [the white tube attached to air box} maybe getting to much air was air cutoff value ok on the side ok of carb?Also check for dirtdopper nest inside the snorkel

 

Honda ATV 2000 OEM Parts Diagram for CARBURETOR | Partzilla.com