Hi

Sorry about delay in replying

Answer is that the position of the vent will have almost no effect whilst the engine is running. With the crankshaft whirring round at 12000RPM, and 20cc of gas trying to get into and out of the breather every cycle the interior of the casing is a very violent place and gravity will have little or no effect.

Once its stopped I think that hanging the model vertically might help a little but dont think its that important. We've had engine hanging around here for years with little or no care and attention between runs and the'yre fine!!