spark plug trouble

I had a similar problem. but i am goood now. To much fuel/oil was entering the engine and it was not all burning off... I did the topend change out as well with a piston to boot.

Check the Spark plug gap... it will foul if the gap is to big...
If the plug is fine, check to make sure the bike is putting out enough spark through your electrical system. Check ur spark... if it is blue, ur good, yellow bad.

Plug 7 is hotter, use it when ur breaking in ur bike and when ur in colder weather or driving at slwer speeds.
Plug 8 is medium use...
Plug 9 is colder for high speed/heat enviroment. (based on the book i read)

Fuel oil mix: I changed mine from 32:1 to 70:1 when I switch to a high quality racing oil. I spend most of mine time at low speed climing mountains.
Check your carb out and make sure ur choke is full off when warmed up and riding. Check the Air inlet screw... is it set to far open/closed?

Hope this helps

plugs

What i would do is check and see where your main jet sits now with the new top end the top main jet on the top of the carb might be to rich move it up and needle and run it if its fine then your good if not move it again. :laugh: i laugh cause i had the same problem its hell to figure it out lol.

ftw666 said:

have a 99 yz 250 and i keep fouling spark plugs
i am running 40:1 mix
brand new top end
full bills pipe exhaust
v force 3 reed cage
main jet 165 went down from a 172
pilot jet 48
needle 1 click from full lean
BR8ES/BR8EG sparkplugs
i can be riding at any speed in any gear and the bike will just die on me and the plug is fouled i dont know what to do
the plug is black and sootie and sometimes wet i have done some carb work but i dont know what else i can do

Click to expand...

Was it fouling before the top-end rebuild; or is this a new issue since the top-end job?

Are you losing any transmission oil? Does it smoke alot? Could be a bad right side crank seal drawing tranny oil into the combustion chamber.

Not sure but it could be your secondary coil going bad? I've heard that a sign of a bike losing its coil is the bike breaking up at high RPM. If everything looks good ie, mixture, jetting, oil seals then check the spark voltage.