I will order a Tach they have a Glo Bee that does 2-3-4 blade props for $28 at Tower. When I was out flying today it didn't find it easy to richen up the engine so it will unload. I was too rich and got a dead stick but it was a pretty landing anyway. If you do this by ear do you just open the needle valve untill you hear a noticable richening or do you just open it 1/2 or 1/4 turn after the highest revs.
This will probably be harder on the TT91four stroke.