bummed out 400 rider

[brianC400X]

I've got a 01 400ex. Its got a full Yoshi, no air box lid, and a k&N.
A while back I took the choke out and ran a 42 pilot jet for a while. I couldnt get it to run right so i put the stock 38 pilot back in.(though I left the choke out) After a few weeks I went back to the drawing board on my jetting. I knew I could go a little further. I went with a 40 pilot. I lowered the needle clip one notch and I put a 158 mainjet in. I got it in the sand and got it dialed in. There was quite a bit more power though I knew i was probably rich somewhere still. I rode hard for 3 days and it ran great. Last night it started cutting out and spitting out clouds of raw fuel. At the time I'm thinking too rich on the mainjet fouled the plug(because you spend more time wide open than anything else on the sand). Today I put in a brand new spark plug in it and It didnt correct anything. It still cuts out and spits raw fuel.

[cheetah]

That sounds a little rich for your mods. I would try going down to a 155 maybe even a 152 on the main. The pilot should be fine at 42 that only control 0-1/8 throttle. I also would double check it with your needle but it may be okay. Just try the mainjet though and see if that works first.

[brianC400X]

That was my next move but I have something else going. It ran good for a few days of hard riding before crapping out. I took the fouled spark plug out and put a brand new one in and it still cut out and spit out clouds of raw fuel. Could some crud jammed somewhere in the carb cause this? If so where?

[Dune Surfer]

Your main could have come out. JMO

[cals400ex]

i agree, your mainjet could have fall out. also, make sure your clip is still on your needle. i know jetting is trial and error, but i think your right on your main. my bike when i had a full x-6 exhaust, no lid, no choke, and uni filter ran best with a 158 in. i would race my friend on his 400ex and compare. this is the one that performed the best for me. i would leave the 42 pilot in. i am running a 45 pilot right now. you said you could not get it to run right, where in the throttle range did it run bad? these are my suggestion even though everyone doesn't agree and temp, humidity, altitude and modifications all make a difference:

main: around a keihin 158
pilot: 42 with 2.5 to 3 turns out on the fuel skrew
needle: stock location (3rd position)

good luck

[brianC400X]

the 42 pilot has been out for a while
currently I'm running a 40 pilot. If I have problems starting this winter ill try the 42 but on the low end of the throttle it seems to do best with the 40. I think that one of you guys hit the nail on the head with the main falling out. I was in a hurry to get riding that day for sure.