low end stumble

[brianC400X]

I have an 01 400ex. It came with a Yoshi silencer and headpipe and a 155 keihn mainjet. Soon after I got it I was searching for more power. I read about removing the choke and installing a 42 pilot jet on this website. I did this according to the instructions from this website. I ride at sea level with no airbox lid. I have a K&N airfilter. After the mod I noticed it liked to pull the front end easier. When I left the house and did some trail testing the thing sucked to ride. Ive lost the power I used to have to instantly spin the tires. It either stumbles or the front tires claw for the sky. Its a real pain in technical trails. I cant control the back end of the quad with power very well because it either stumbles or does a wheelie. I've been playing with the airscrew for days and I cant seem to find the sweet spot. Your thoughts would be greatly appreciated.

[cals400ex]

i think you may be alittle small on the mainjet. do you already have the 42 pilot in? where is the needle set at? does it run good at top speed?

[JOEX]

Cool, another left coaster. Welcome to the site.:)

I agree with cals400ex. Answer his questions and we will have a better chance at helping.

Joe

[brianC400X]

I talked to the guy who i bought it from today as well as posted here. He put a 155 mainjet in because that was what yoshi recomended. I installed the 42 pilot jet when I removed the choke. I didnt touch the needle. It feels good at speed but I havnt ridden enough 400ex's to know what it is supposed to feel like. I emailed Yoshi's technical support(i saw the link on thier website). I'm hoping they reply to my summons.

[JOEX]

A 155 might be a little small for a full system and no lid but the main jet only affects 3/4-full throttle.
I'd suggest raising the needle on notch (lower the clip one notch).
Set the mixture screw at 2 1/2 turns out. See how it runs then play with the screw a bit.
Have you replaced the spark plug lately?
It is best to change one thing at a time, not that I always do it that way:p

Joe

[cals400ex]

i am honestly wondering if i lost a little power by removing the choke. your 155 main is probally good for your pipe. however, you have a K&N and are running without a lid. i would go out on the fuel skrew a little bit. my headers glow and i have an x-6, uni filter, no choke, and no lid. the thing is i am running a 45 pilot. i need to be at least 3 turns out on the fuel skrew or my header will glow at low throttle positions. i know this sounds dumb, but i think i will be putting that choke back in on my bike.