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Hey guys, hoping someone could help me out because i'm running out of ideas. 05' KFX 400 I bought 10 years ago. Guy I bought it from said he put a big bore kit on it (not sure of the size just guessing 440 but I cant remember) and exhaust, said he had it professionally tuned, jets resized etc... Ran great for several years until I let it sit to long and the carb gunked up on it. I started to tear apart the carb to clean it, had a family emergency come up and the bike sat for another year, meanwhile the carb and petcock got lost along the way. So I really have nothing to compare to, jet size, hose routes etc..

I went ahead and ordered a new carb and petcock off amazon and threw those on there. Immediately I noticed a few things wrong, it does not have a place to put the TPS sensor (I've read this doesn't matter), it does not have the traditional choke lever like the old one, I guess its automatic...? and it has a vacuum port that I thought went to the petcock but the new petcock does not have a vacuum port, so I just capped this off.

It started right up, will idle perfectly after a bit of throttle adjusting. Problem is at wide open throttle it bogs way down. If I smash the throttle at idle it pops/cracks and backfires flames out the exhaust. (I'm guessing running to rich?) I've adjusted the air fuel screw on the bottom of the carb 2.5 turns out, and have played with it .5 turn in and out to no real change.

I removed the seat and the quad started to run slightly better, I then removed the filter and took a pass and it ran a little more, finally I removed the intake tube from the carb completely, so completely wide open with absolutely no restriction and it finally started running at WOT. It's like the slightest restriction in air will bog it down. Even just putting the intake boot on the carb with no filter on it, so its just about wide open and it still bogs down at WOT. I can see completely through the intake tube so there is no obstructions there.

Any suggestions, I'm thinking i'm running way to rich but don't know how to fix it. I would think with the stock carb I bought if anything it would run to lean with smaller jets? Carb and petcock I purchased below:
74608
74607
 
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