Since I havn't mounted the engine yet, I think I'll try running it on the bench w/o the muffler to see if I can get it tuned. It's an ASP .65, probably the same as your Magnum 61. I heard they are manufactured at the same place. Its my first 4stroke so it may take me a while to get used to any tuning or adjustment differences. It just seems to me that if you dont pressurize the tank the engine may have problems drawing fuel on high G manuevers,especially on aerobatic planes. Have you ever experienced this?