I've just completed a model P51d Mustang and have put in an OS 40 fp engine. the plans say for it to br upside doen. this has now put the pressure nipple on the muffler on the UNDERSIDE of it. Burnt oil seems to be getting into the fuel tank now. Would that be causing it to run spasmodically, i.e. increasing and decreasing in revs, then sometimes cutting out mid flight? Should I re-tap a hole on the now Top of the muffler for the pressure hole? thanks!!