Motorcycle Repair: Fouling plugs, mixture settings, stroke oil

Question
I 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

Answer
Hi Steve.
 You may be in need of new rings.  Has the bike been seeming to run with less power than before this problem occured?  How is your air filter?  Is it too dirty?  These things will adversely affect your bikes ability to burn off the fuel properly.  If everything is set to factory recommendations, then it should run correctly.

Make sure that all of your mixture settings are correct as well, if you can and make sure that the oil/fuel is mixed correctly and you are not using out of date oil in the mixture.

Other than that, I am not sure what else it could be.

Good luck.
FALCON