The oil content of your fuel should not be the source of your problem That engine, when properly broken in, will easily run at a lower oil content -- the the level you us for the big Super Tigers, but definetely with the level in Byrons.

I agree with the other posts -- it sure sounds line fuel line. BTW, putting in a large klunk won't help unless you make everything else large (klunk fuel line, brass tank line, and fuel line to the carburetor.)

Also, what is the relationship between the tank and the engine. You want an optimum setup with the tank less than 12" from engine and the level with the carburetor. If that is not the case invest in a Cline Regulator.