I have a GP Matt Chapman Cap 580. I've installed a Tower 75 with a Bison Pitts muffler for a GMS 76. After warm up, engine stalls at no particular time, idle, mid range, wide open throttle. I've tuned it many times. I have changed glow plugs, fuel tank, lines, ran it with and without the engine cowl. I have event tried another Tower 75 using the same Bison Pitts muffler. I suspicion it is overheating. Both these engines are broke in and have ran fine in other planes with there stock mufflers. I am using the same 15% Omega fuel that I broke these engines in on. The engine in this cap is mounted horizontal. Any body have any suggestions to correct this problem? I like the Tower 75 and the Cap 580. I would like to make it run in this plane before changing to another type of engine.

I had a similar problem with a K and B 40 and a slinline pitts muffler. Not enough pressure , in my case anyway.
I could literaly take the high end needle all the way out and it would still run!
I closed off one muffler tube, and the problem was solved. Been runnin it like that for 15 years.
You only need an exit hole the size of the carb intake. the motor is nuthin but an airpump.
Perhaps you could try it at least, and see if it works for ya. Hope that helps.
d

I run a Tower .75 with the same muffler as mentioned and have no problems whatsoever. Is your tank in the correct location. If so block off the air inlet on the opposite side as the head. The air will otherwise take the least path of resistance "not over your engine". I blocked oneside on my shoestring, and it dropped the incowl temp about 40 degree's. My clyinder head temp now runs about 225. Also make sure your outlet allows 2-3 times as much air out as in. My temp originaly was hovering in the 265 area, but I still have never had a dead stick or flame out. I am running the same #8 plug that I broke the engine in with and the plug was used then. I only run 10%, and I am on the fourth gallon this summer. I love the engine/muffler combo.

FYI,
The pitts from Bisson supplies plenty of pressure. This is an installation problem, not the engine or muffler. MY enigne runs @ 2-1/4 turns out, and I seldom ever have to touch it.

could also be that the slow needle is moving around/had that happen too.
d

Im on my second tower 75 and have had the same problem on both.i sealed the back plate with a gray type sealant ,i also sealed the fuel nipple going into the carb.make sure the carb is down tight on the motor and move the high speed needle to the carb.i also placed a small piece of fuel tubing over the high speed needle so no air could leak in.before this i was doing what you did.now it runs great except for a rich mid range but thats what the first one did to.the first 75 became my favorite because it was the one i could count on to be trouble free every time i took it out,until it ate the front bearing.i sent it back in under warranty and got a new one,my second one,but this time i knew what to do to fix the problems.i have it on a beat up harrier 46 with a half a pound of extra weight in repaired balsa and covering but it goes vertical like a rocket.hope this helps

Sounds like not enough back pressure by the muffler to pressurerize the tank. Try the fix mentioned above and block one exhuast pipe. I had the same problem with that muffler. Wayne

When all else fails, make sure the pressure line nipple on the muffler is tight.

Have a Supertigre S75 with a Slimline muffler in a Pica FW-190D that runs like a top, until one day when I'd go full throttle it would run for a few seconds and then just go Waaaaaaaa and quit, as if someone pinched the fuel line shut. Changed plugs, fuel, you name it....finally found the pressure nipple in the muffler to be loose.