Hey guys I’m new to the site I have an ‘07 400ex only mods are jet kit, k&n air filter and HMF exhaust. The problem I’m having is that it’s VERY cold natured. It doesn’t wanna idle at all and I can hear a light knocking sound but when it warms up everything smooths out and runs fine. I can ride it for an hour or so then let it sit for just a little while and it’s like it’s cold all over again. I’m kinda thinking the jet kit may have something to do with it the previous owner done the jets so I have no idea what size they are. I would greatly appreciate any input u guys have. Thanks

Ok guys I decided to clean carbs and go up to a 42 pilot jet and while I was at it I adjusted the valves and now it runs ok but when going from idle or low rpms to full throttle it bogs and I’ve noticed it’s blowing air out the air box when I give it throttle it’s enough to lift the air box lid if I don’t strap it down. It’s also running rich it turns the plug black and it’s the factory 148 main jet just make no sense. I’ve went thru the carb 3 times to make sure everything is right and I’ve readjusted the valves tight, loose, just right and nothing seems to make a difference. I also done a compression test and it’s good 120psi so I wouldn’t think it’s a valve. Please help!!

Even though it’s running rich with a 148? I tried a 160 and it seemed to make things worse so I went down to a 145 with same results so went back to stock it’s seems to do the best with the stock one for some reason I can’t figure it out