ORIGINAL: Dean in Milwaukee
Just an update for those you think their gms .47 fuel supply might be due to their fuel system and not the motor itself:
Installed and ran through 2 tankfulls on the ground of my gms .47 replacement, the magnum .46a, then leaned it out properly, richened it to lose about 300 rpm and went nose up, and the leanout/quit problem was...........gone completely. It was indeed the poor fuel draw of the gms .47 that was causing the problem, not the fuel system.
As a side note also proving the poor fuel draw problem, when you prime the magnum .46 by opening the throttle, covering the carb air inlet with your finger, and slowly turning the prop till you see fuel in the line make it to the carb, the magnum .46 takes about 2 motor revolutions to get fuel to the carb where the gms can take 10 or more, and once you stop turning it over, on the gms you can see the fuel immedietely start flowing back to the tank where on the magnum it stays full with no backflow.
I don't quite get why it backflows, but it does.
Dean in Milwaukee
Wayne:
Good refesher to tuning an engine[sm=thumbup.gif], but I was referring to the last major discussion, regarding fuel rushing back to the tank. In an earlier thread, I had remarked how GMS engines are not the only engines that can be accused of having poor fuel draw, and that a couple other engines(non GMS) that I was working on were having fuel draw issues, and that after you primed them, the fuel was rushing back to the tank. My last entry was describing what I had found to solve the problem "in general", and not specific to the GMS. I was pinpointing the condition of the carb, and not the engine. The K&B carb was a total loss, and required the installation of a Perry to stop the backflow of fuel. The O.S. carb required a good cleaning. Hard to say if it was dirt or dried castor build up, but a good cleaning solved the backflow issue, and the flameout issue at high throttle. The two issues seemed to be related. I guess my hole point was that there are some problems that are related to engines in general, that some people may be trying to stick on the GMS line alone. I don't see any fuel draw issues with my GMS's, and wonder if a good carb cleaning wouldn't solve some of these problems. I am sure some problems were solved by replacing the carb body, due the bad location of the spray bar hole. I am sure Wayne and others would agree that you can get a new engine from any manufacturer that could have a blockage in the carb, that would cause a fuel draw issue. If the engine ran fine and all of the sudden doesn't, look for the obvious first. I would consider the obvious to be:
1) a clunk that has fallen off
2) leaks around fuel fittings
3) holes in fuel lines
4) bad plug
5) kinked fuel line
6) clunk that has become trapped at the front of the tank
7) throttle servo that hunts, instead of consistantly returning to its programmed position
8) fuel line that is too large for the application(can help generate bubbles)
9) Leaking tank or tank stopper
10) Carb not fully seated
11) Cracked or torn O-ring at base of carb
12) Help me out guy's,... there is bound to be another dozen EZ solutions. Anyone care to add any?
After checking the EX fixes, then tear the carb apart and clean. If that doesn't fix it, then it is time to get more radical.
