Well !!! After changing glow plugs (now have a Sonic-Tonic plug) and getting the low and high needles close to being correct, I have had several good engine runs (and flights) on the Bluehead in my Aeromaster. I have been using the old Dubro baffle plate muffler. Of course it is to loud for today's standards.
Today I put the Mac's back on without changing anything else. The first thing that happened was the engine ran very rich and died. I removed the tank pressure tube from the muffler and the engine started running correctly after a minor needle adjustment. However, the RPM dropped from about 12000 to barely over 10000. (Running a Top Flite 12x6 and using an old Heathkit thumb tack, so not to accurate). I than put the pressure tube back on and turned the high needle down until the engine started running right. The needle felt like it was all the way closed or very close to it. The engine ran fine when I flew the Aeromaster but it just couldn't hack it at only 10000 RPM. So I put the Durbro back on.
When I got home I drilled out the outlet hole on the Mac's muffler as much as possible. Also the interior hole on the baffle tube. It just about doubled the area of the outlet hole, maybe more than doubled. I am now ready to try the muffler on the engine again to see if the RPM gets close to the 12000 I was getting with the Durbro muffler.
I'll let you know as soon as I get a chance to run it, probably in a couple of days.
Ralph White, Neoga, IL