RCU Forums - View Single Post - GMS Engine Tuning Problem
View Single Post
Old 10-26-2004, 07:05 PM
Wayne Miller
Join Date: Sep 2003
Location: DrumboOntario, CANADA
Posts: 1,286
Likes: 0
Received 0 Likes on 0 Posts
Default GMS Engine Tuning Problem


I have two 2000 GMS .47 engines. One is older, that I just got, and I also have a new one. The new one has a muffler with fins and works fine. The older one has a muffler with a polished center section and is giving me problems.

I put the older one on a SE and took it to the field today. I'm using 15% fuel with synthetic/castor and the engine has about 1 gallon of fuel through it.

I had a very difficult time adjusting wide open throttle, however the idle adjusted fine and would shut down at low throttle with no problems. Transition from low to high throttle is good. The problem occurred if I left it at wide open throttle - it would all of a sudden stop (no warning) as if I had a fuel blockage, or fuel pressure problem. I noticed it was not over heating (not too lean). I checked tank, fuel lines, clunk, filter and checked needle valve and seat for contamination - all were clear. Also checked for leaks in fuel line, and pressure from muffler - all is OK. I also changed glow plug with same result, but RPM was slightly better.

I found the wide open throttle adjustment was very broad, like one turn either way, and never did seem to really peak. On my new engine the adjustment is very touchy - like two clicks either way.

From reading the posts here at RCU I remember that GMS had an air leak problem. So I returned home, put a new "O" ring on the carburettor then mixed up some soap and water. I plugged all openings on the engine (exhaust, pressure feed, carburettor intake, and fuel intake).

I then sprayed a little soapy water on the engine. Hooked up fuel line to the carburettor intake and blew into it with all the other openings sealed so there was no place for the air to escape.

I could see soapy bubbles (air leaks) at the carburettor retaining bolt as well as a very small amount at the front bearing.

I sealed the carburettor mounting bolt with copper RTV, and also the carb "O" ring for good measure.

I still have a small leak at the front bearing.

I'll see how it runs tomorrow, but I thought I'd check here to see if anyone has any other suggestions, or experince with the same problem.

Thanks for your help,

Wayne Miller