Right now i think it has a Master Airsrew 9x6 on it, when i figure out a new muffler I am going to change the prop and spinner to a new one and see if it happens to be the prop. I have a friend who has some old mufflers and we are gona go thru them sometiem and see if one will fit it! (Thank God for packrats!!) I appreciate teh help and will let you know what i come up with!