Yesterday afternoon, a club member had his new ST G.51 out for the first runs and flights. On a TF "Tooter Too" (sic) ARF, but that's not important. Nor is the engine brand, actually.

First flight, after several ground runs, it started out very nice, but about halfway into the flight, it went lean. Not REAL lean, but peaked. After the flight, I retreived the model and noticed that the muffler gasket was hanging on the muffler pressure hose. 
Hmmmmm....blown muffler gasket causes leak > causes reduced pressure to the tank > causes  lean run.

Moral of the story is: IF you think you just gotta use muffler pressure, beware of this potential consequence. Also, skip the muffler GASKET. Lap both surfaces flat and smooth and maybe apply a very thin film of high temp silicon gasket stuff before assembly. Use better bolts than the slotted head screws that come with the engine. Any leak in the joint will at least be consistent, as long as the bolts stay tight. Make certain they do!

By the way, the ST G.51 is WAY more engine than the Tooter Too needs. And the (huge, ugly, heavy, complex, etc.) stock muffler, while a great candidate for the recycling bin, is very quiet. One redeeming quality, at least.   Steve

The Super Tigre muffler gaskets are worthless.  I have a GS 40, and I couldn't get a gasket to last through one flight.  Went the red RTV silicone route and no problems since.  Glen

Better yet never use a muffler 

Old Racers never die or hear too good 

Scott