QuestionI have a 1987 CR250. When I put in a new stock plug BR10ES it fouls within the hour. Runs great while it lasts. Doesn't matter if I idle or rev up hills. It looks oily. When I put in BR8ES it never fouls instead it pings under extended heavy load like riding in sand. I guess this is to be expected as the plug is too hot. It looks white. Any suggestions? Don't say get a BR9! Then I'd have the worst of both? Too rich? Adjust needle clip? Old 2-stroke oil? Mix less than recommended?
Thanks in advance,
Steve
AnswerPlugs foul either due to being out of the heat range for the application of excess fuel/oil.
If the bike pings under load, either the spark timing is too advanced, the fuel octane isn't sufficent, the mixture is too lean (jetting, needle position or air leaks).
Check your piston for signs of seizure or worn rings. If you are forcing a worn out motor to do what it isn't designed to do, then other failures may be in the offing.
These things are designed as race bikes, not trail bikes or enduro machines. They are highly tuned and very sensitive to settings and the condition of the engine components. If your bike has been modified in any way from the stock configuration, then you have to adjust the carb and timing to match the modifications. Carbon build up in the exhaust system and cylinder head/piston can drastically affect the performance, so keep an eye on the exhaust port and pipe condition.
Use a quality 2-stroke oil and premimum gas for your fuel mixtures and follow the suggestions of the oil's manufacturer. If you don't get the results you expect make small changes and monitor the outcomes.
I am not really and MX expert and you can probably get more info from www.vintageiron.com or other vintage MX sites.
Bill Silver
