I have a 1998 YZ400f i just recently got a few months ago. It runs awsome and is an all around great bike!

but... about ever couple of rides (a hour or two each) i foul a plug! (iv'e gone through 3 now)

the plugs are all carbon fouled.

when it runs it runs awsome, but you'l go to start it up the next day, and it wont even fire.

i have already leaned up the neetle jet a notch and the pilot jet a bit too, and i'm waiting to see what happens.

is this all i need to do, or do i need to make furthur adjustments?

Thanks, Michael

I have a 1998 YZ400f i just recently got a few months ago. It runs awsome and is an all around great bike!

but... about ever couple of rides (a hour or two each) i foul a plug! (iv'e gone through 3 now)

the plugs are all carbon fouled.

when it runs it runs awsome, but you'l go to start it up the next day, and it wont even fire.

i have already leaned up the neetle jet a notch and the pilot jet a bit too, and i'm waiting to see what happens.

is this all i need to do, or do i need to make furthur adjustments?

Thanks, Michael

hi had same prob myself ,on fzr600 the idle mix was set to rich and the unburnt fuel was carbonizing on plugs couldnt start it next day ,check to see what manual says how many turns out it should be ,thats a starting point mine was 3 but its actually at 4 now the older the bike the more you have to tinker also check to see if air filter blocked that would also stop air getting through . let me know how you got on hope this helps john