Hi FlyboyDave,

Do you have an exhaust extension on your muffler? One person at our field does, and it this improves exhaust pressure for the tank - we think it may be the bend in the extension that gives a slight restriction to cause more back pressure - just a thought.

Another comment at the field was that the pressure nipple may be close enough to the front of the muffler to create a venturi effect, thus it may actually be causing a vacuum at the pressure nipple. I can't comment on this, but the baffles would help if this is the case.

I took a look and measured the "new" muffler with fins that works OK with the GMS .47. The body of the new muffler is smaller in diameter, but there is a slightly larger exhaust opening (.3 in compared to .25 in).

I wonder if the smaller diameter of the muffler body gives enough back pressure to cause more pressure to the tank?

When first starting up the engine, and without modification, you can see the "bubbles" on the pressure line of the "new" muffler moving toward the fuel tank. However, with the "old" muffler the "bubbles" were either stationary, or moving exceptionally slow.

It was mentioned that perhaps there could be a blockage or kinked pressure line, this was one of the first things I checked. It was visually clear, and fuel flowed freely out of it when refueling. Last night I also removed the tank, took off the stopper, and checked the lines and "clunk" just to make sure there was no air leaks and made sure the lines were routed without restriction.

All I can say is that with my new makeshift baffles, all is OK and the tank seems to be pressurizing OK, and the engine works very well.

I've heard a lot of people complain about the older problem GMS's, and other than sealing the air leaks (which may or may not have worked) there has been no definite fix.

I'm hoping that the baffles "fix" may help someone else who has previously run out of options. It is a great engine when it is running properly.

Thanks for your input.

Fly4Fun,

Wayne