I am running in an O S 30 S on all methanol with 25% castor and about 3-5% synthetic, and I have some problems with it putting 4 ounces of fuel in it it will run 6-7 minutes, but at about half the tank it speeds up, every tank does the same, I measured the venturi and it shows .282-.283 in diameter, what should be a good venturi size for it?  Oh, I am running a 10x5 wooden prop also, and it has about 25-30 minutes of run time on it, at about 8000 - 8200.  Looking for help/suggestions to get a more consistant/steady run.  All help appreciated..

  I don't think the filter is stopped up as it does the same thing every time..