Hi AirGar,

Just an update.

I was flying today and all went well with the baffle in place.

However, I put a lot of thought into the problem and when I got home, I decided to dissassemble and take a look at the differences between my "old" and "new" GMS engines fuel delivery systems.

One of the things that did not look right was the fuel opening into the carb under the fuel nipple (the one the fuel line attaches to). It did not seem to quite line up with the hole from the fuel nipple.

To explain, if you take the fuel nipple off of the carb body, you can see a brass insert under it in the carb. The brass insert has a hole in it. The hole in brass insert did not quite line up with the hole in the fuel nipple. It seemed to pass air OK, but I'm not sure about how it delivers fuel. This could be causing the fuel restriction at full throttle - I'm not sure yet, I still have to test. But this would explain why more muffler pressure helps at full throttle.

I then reassemble, attach a fuel tube to the carb nipple, and blew with the throttle wide open, and needle valve backed out a little. I listen to the amount of escaping air.

I then removed the nipple again and carefully hand drilled (not electric - I didn't want to damage the threads for the nipple) through the brass so the hole to the carb was slightly larger. I inserted a pipe cleaner into the needle valve opening to catch the brass particles.

I expected that if this slight restriction, due to misaligned holes, was causing the problem, this would allow the fuel to flow freely into the carb from the nipple, since the openings now line up.

I also drilled out the fuel nipple and exhaust nipple to the next size larger - I figured this wouldn't hurt anything, and may help. Now when when I reassembled, put the needle valve back to the last setting, and did the "blow" test at full throttle, more air escaped with less resistance.

I don't think I'm going to be flying this week end, but if I do, I'll let you know what the results are. I expect the engine to perform better, and I may be able to remove the baffle.

If possible, would you mind carefully removing the fuel nipple from your "bad" engine and see if the hole in the brass insert in the carburettor lines up with the fuel nipple?

Hopefully we are getting closer to solving the problem, I let you know my testing results as soon as I know.

Thanks for your help.

Fly4Fun,

Wayne