QUESTION:----------
I have a new 2003 yz 125 that I ride trail on and when i put a new plug in it runs good but after i stop for an hour or less it well start back and and ride for about 20ft and then "pop pop pop" It fouls when i pull the plug it is wet and dark.. ill be lucky if i can go a day without fouling one.. im 15 and live in eastern kentucky and i mix at 32:1 with yamalube 2 cycle racing oil so what do i need to do?---------EXPERT VIEWS ON THIS PROBLEM:------------
ANSWERS:--
i had a similar problem, but a 2003 KX 125, fouled abt 20 spark plugs in the first month of having my bike, they changed the coils and fly wheel. Wasnt that. then after abt 2 months of experimenting, they found it to be the spark plug cap.
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hey i have the same bike just adjust the pilot air screw your running it way too rich you need to look in your manual and find your screw then tighten it all the way but not too tight then turn it bout 2 1/2 time out the further out you turn it the richer it runs. That will fix your problem you might also want to use NGK BR8ECM spark plugs thats what fixed mine.
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i suggest jetting first and maybe use 32:1 thats what i use. if all else fails it could be your crank case seals if they are stuffed gearbox oil can leak into the combustion chamber i had this problem with my old 2000 yz125 a few years ago.
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i dont know why you are mixing 32:1 i mix 50:1 but i use thumper i found that it is a very nice mix it sound like you are running to much gas in it i am suprised it has not blown up yet.
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Buy some fully synthetic 2 stroke oil, all ur proplems will be solved. Yamalube is the wrost oil u can use.
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Yamalube is the worst oil you can use in your bike. It doesnt matter how you mix it 32:1 or even 40:1 it will foul you plugs. I recomend using a fully sinthetic oil like motul or Silkolene. Try these and youll be back to having fun on your bike, and dont forget to use a BR8 plug.
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Before swapping fuel's and plugs get your jetting right, then it will not foul quickly, though if the plug is too cold for your riding style it may carbon foul over time and a hotter plug would be a good fix, I'd recommend a BR8EIX in that case. The real problem is your fuel mixture, not your plug, oil or riding style. Jets are cheep and easy to install. I'd recomend droping the needle one notch, going down one size on the main jet and turning the air screw out half a turn for starters. Keeping a bike properly jetted will improve performance and reliability far more than anything else on a race bike. Also, I'd run 36:1 for the 125's.
SEE FIG BELOW:---
On carb will be a screw turn this in 1/4 of a turn with the machine running until it idles the idle
