my engine (o s 35) runs great at level flight both upright and inverted. (it's mounted inverted in a nobler). with plane flying upright performance is a good classic 4-2. perfect. but when inverted the slightest up attitude the engine runs far leaner thus faster. return to level flight it's back to normal run again. how can i remedy this. no muffler pressure.

Louis, if it still has the same round tank (Sullivan R-4) I put in it, the uniflow tube is fixed on the outboard wall. 
Rotate the whole tank CCW looking from front, to lower u-flow about 1/8".