ok here goes, I have a 96 Kodiak ymf400 4wd. The quad used to run great just smoked like a freight train so I did a top end rebuild and rings. fixed my smoking problem. while it was out I went ahead and re-cleaned the aftermarket carb on it(which always ran fine) but now It pops and back fires any time above 1/2 throttle and while decelerating. it will push through the backfire and keep going but its pretty bad. I pulled the choke and did a pull which tells me it is too lean so I've been adjusting the needle but 1 and 2 clicks richer only makes it run worse. which makes no sense to me. how can it be to lean but richening it makes it worse? it has a new plug, the cam timing and valve clearances are spot on. what could it be. the only potential issue I have found is when I plug the intake with my hand it doesn't shut the bike off.. should it? also when I had the had off I cleaned the valve ports by hand because they were terribly corroded. ive adjusted the carb every which way and nothing seems to help. maybe I need a bigger main since the air flow is so much better but I really don't know and jets are hard to come by and not something I want to guess at. any help is appreciated, thanks in advance guys.

 

I would guess at either the inlet or exhaust manifold joints are leaking and letting air in. May not be, but it is worth checking.