2003 Yamaha 125 yz plug fouls pretty quickly. running 32/1 fuel oil ratio, and using NKG plug 2411/B8ES. Do we need to run a hotter plug?

Some guys will tell you to go to 50-1. Don't. 40-1 would be okay. If that doesn't stop the fouling, go to a hotter spark plug. An example would be BR8ES to BR7ES. The lower the number, the hotter the plug. By the way, you ARE using two stroke ENGINE oil and not MOTOR oil aren't you??? Please rate my answer.

What is causing the fouling? Engine oil? On a two cycle dirt bike, the fouling can be caused by excessive oil in fuel mix. I believe 50 to 1 is the correct ratio yet you may want to cut back, a little at a time, on the oil or run hotter fuel. The exhaust system will also accumulate enough oil sludge to impede the exhaust flow causing poor performance and plug fouling. A two cycle must breath freely to keep itself internally clean. Air cleaner to exhaust. Proper fuel mix should have little , very little. Good Luckand hopefully this helps you.

32-1 fuel to oil. 0.5 to 0.6 mm gap.

Run a B9ES if you don't have a problem with fouling. If you do have a problem fouling, run a B8ES. Both of these plugs are available at auto parts stores for a few bucks each.

The stock plug was a BR9** - the R indicates a resistor plug which is not needed.

Scott

Two things could be at fault here. First - it's a good possibility you would benefit from a new top end. Top ends go away fast in these because they are single ringers. Under hard riding, the compression starts to fall off after just 2 hours. Poor compression means lower combustion temperatures which will lead the bike to run rich.

The other possibility is that your jetting is off. If you have had this bike for a while and it's always run well then slowly started to act up, its likely poor compression, but if you recently got this bike and do not know the history of it, then it could be a simple jetting issue - not at all uncommon for 2-strokes.

Also - no need to run the BR8EG. This is a resistor plug and is a higher performance plug. If you are a top Pro rider, you could feel the difference but for 99% of riders they could not tell the difference between a BR8EG and a B8ES. The B8ES is readily available from auto parts stores (NGK stock #2411) for $1.89 instead of $12+ for a EG plug form a bike shop. This info alone could save you a bunch of money. Keep in mind the stock plug is BR9EG, so you are running one step hotter which is fine.

Also keep in mind there is a lot of information that I do not know, nor do I know the overall condition of the bike. Internet diagnosis is always tricky, but I thought I would point these things out. I hope this has helped, but if not - we need more detailed info to properly diagnose the problem.

Fouled plugs are typically caused by jetting that is too rich. This could also be from a dirty air filter which can make the bike run rich. Clean up your filter and see if that is it. If the filter is not too bad, you might want to drop a size on your pilot or main.

Another possibility is poor compression - this can make a 2-stroke run richer than normal as the fuel can not be burned properly. Rings don't last long in these 125s. I used to re-ring each week when I was racing 125s.

You might want to run a B8ES plug, too - this is one step hotter and will help the plug from fouling as often.

first off make sure the oil gas mixture is correct and mixed very well.... have the carb cleaned out very well or even rebuilt, jetted and adjusted...