YZ thats likes to foul all my plugs

[WhyZee250dude]

Lately; my 04 YZ250 has been fouling plugs at the start whenever you give it gas...the only way to get it going with the same plug is to let it idle and slowly rev it up over like 5-10 minutes till it sounds like you hit a powerband and will work fine after that. Its becoming a nuisance and was hoping someone might know the problem and/or solution.
\Thanks

 

[Jaybird]

If the bike had been running fine, and this just started happening, it may well be that you have a leaking seal. The tranny oil could be what is fouling the plug.

It is also possible that oil could be settling at the bottom of the tank, and a massive dose is what the carb sees right off the bat, and cold fouls the plug before it is up to temp.
Try shaking the bike real well before you open the petcock next time and see if things are ok after that. You are closing the petcock off after you ride, yes?

 

[WhyZee250dude]

i think you are probobly right about the seal because ive done everything else you mentioned and the gas is brand new. What is this seal? Do you replace it? Is it easy? Appreciate it...

 

[ziptiedEXC]

He is talking about the main bearing seal. Some bikes you have to split the case {KDX} and other bikes you don't {96' CR250} I don't know about your YZ.

 

[littlenasty]

i am fouling plugs alot too, and i am going to try and switch to a 34:1 ratio and see it that helps

 

[WhyZee250dude]

Could It Also Be Because Of A Few Dents In My Expansion Chamber?