I have a 86 TRX250r. I just rebult the top end its bored +.020 and has a wiseco pro lite piston. I also put new boyeson reeds. It runs great when. I was breaking it in I ran it a little rich for about 2 tanks of gas. I run bel-ray synthetic racing oil and premuim pump gas. The bottle says 50/1 ratio with 5 gallons of gas.(I put 5 gallons in.) It runs rich and fouls out plugs. I ride it for about 2 days and the plug is black and it won't start. I went from a #9 NGK plug to a #8 hopijng this would help it didn't. Any sugestions??

 

I have NEVER had any luck with NGK plugs, although that is what EVERYONE uses. I use Champion, NC2 or NC4. Regardless of the plug brand, you are still to rich. I would set your needle clip in the middle postion, then reduce the main jet size. I use Amsoil 2 cycle at 50:1 and have a main jet of 152. I wouldnt drop that low right off the bat though, only drop one or two sizes from what you currently have. Run it and see how the plug looks then.

 

Did you put a rad valve on or just the reads?

When I put my rad valve on I had to drop 2 jet sizes as it made to bike run rich.

 

Well 50:1 is a lean mixture ratio. But since there is less oil the fuel/oil mixture will be thinner so your motor will actually run RICHER than it would at say 20:1 because since the fuel is thinner the mass flow rate of the fuel through a control volume (i.e. main jet) will be higher due to less viscous drag. Water pours faster than syrup!! this is due the viscosity (neglecting the H-bonds causing surface tension) being lower. Also the lower the viscosity the higher the Reynolds # this will also contribute to a lower coefficient of drag. You could either fix this buy running a richer mixture . I would recommend this anyway beause your main bearings will last much longer. Or go down a couple of sizes on your main jet and drop the needle and raise the clip a position. This should fix it. Hope this helps

CT250R