But I don't think your fuel/oil mixture is the problem, the problem is most likely your carburetor settings. Telling you from our point of view how to set up your carb would be plain stupid, we don't know where you ride, how you ride, the oil you use and about the condition of your engine. When you're jetting a carb, there's not really a secret formula, it's more of a trial and error and going from what the manufacturer recommends in either direction to suit your needs, heck... when done 100% right even the quality of oil is crucial, because the best oils aren't always the best for a particular rider.
zebzone235 wrote:2003 RM250, hopped it up with a Keihin AS-38
Most 250 2 Strokes of that time came with Keihin PWK38 air striker carburetors, so did the RM250s, what carburetor came with it when you bought it, because obviously you went back to the stock carburetor?
I'd try to clean the pipe and repack your silencer(it's most likely soaked with oil), check the powervalve for carbon deposits or unburned oil, run 40:1 Motul 800 or Motorex Cross Power 2T(IMO they offer the best overall package) and eventually pick the right main jet, needle position and dial settings. But again, jetting a carburetor is as personal as buying yourself the right undies.