My buddy has a 99 400ex with a stock carb and he just got it bored 20 over cause it needed it. He put a Big Gun(header and silencer) hes got a K & N air filter with no air box. It ran fine before the bore, but now when he got it back, we knew we needed to jet it but we cant figure it out at all. We went and bought 3 diff jets. It had a 190 on it, we went from that to a 195, then 200, and then a 220. Its cuts out real bad about 3/4 throttle. We moved the clip on the needle and that helped alot but it still starves on top end. When we took the plug out to check it, its running lean and the plug is pretty silver grayish lookin. I know that tan means its running fine. We took that 200 and we took a dril bit and drilled it out alot (probably a good 230 now) and still runs lean and and cuts out. Could someone please help me, we would appreciate it alot, they are goin to the Badlands this thursday (spring break). Thanks

 

A friend of mine had the exact same problem after his 440 and cam install. He went up to a 220 main as well, and it was still real lean. He ended up solving his problem with a 39mm FCR carb.

 

Are you for real or is this a late April's fools joke with those main jet numbers? If you are for real and using those jets, there is no way the 400 or 440 will run.
If you realy do need some help, try a 45 piolet and a 160 to 165 main. Make sure that you a re taking a good plug reading the correct way. If you have to use jets that big there must be something else wrong, I think.

 

YEah we're using those jet numbers. And all we did was start it up, and rev it up a couple of times. We didnt take it down the driveway or anything. It kinda sucks cause we need to get that thing going. I think we will try that thing with the pilot and jet. Thanks

 

Your whole throttle range is to lean. U need to rejet from the bottom end to top end. I would go up 2 sizes on your piolets, drop the need clip postion, and go a couple sizes bigger on the mains. Revving it up in neutral isn't going to work. U need to drive it around in all throttle postions.

 

No joke. Dead serious. I helped with the jetting and tuning. As for your suggestion on running a 160 or 165 main, I'm running a 172 main on my XR cammed, stock piston 400EX and mine is still just a tad lean on top. I'm at 1100 feet with no airbox lid. We spent a whole weekend at Glamis trying to tune my buddy's XR cammed 440EX. It finally ran okay with the lid on and a 220 main. It flat out rocks now with a GT Thunder cam and a 39FCR.

 

well, they figured out some of the problem. The timing was off 2 teeth on the cam sprocket i guess. Its still running lean though with a 195 main. Should he go with a 45 pilot and 160-165 main, Or even go bigger with the jet numbers ?? Its just a .20 overbore with K&N and no air box lid. I dont understand how it is the way it is. If i could get some more advice, we'd really appreciate it. Its seems to run great, its just its running lean. Thanks