Firehawk153

I've replaced my old engine on my aircore 40 with a GMS .47 but I'm having the darndest time getting thing to stay running.

I put everything in new; new fuel lines, new fuel tank. I have already broken in the engine and I have no trouble starting the engine but the engine will quit every so often (I haven't flown with the new engine yet). It seems like that whenever I go from idle to full throttle the engine will kinda stutter for a minute and then it will pick up speed and go the faster RPM. I've switched out the glow plug with a new one and that really didn't seem to help.

One thing I've noticed is that when I've got her stationary she doesn't do this...its only when I start taxiing that I have this problem. I'm guessing that something in the fuel line/fuel tank setup has a leak and when she gets to taxiing and shaking around that it exposes the leak and makes the engine quit. That's just a guess...anyone have any suggestions?

Thanks

n19htmare

My Feedback: (1)

Seems like you need to lean out the low speed or the idle needle just a tad bit. If it stutters before going to full throttle, it's because there is fuel loading up in the engine (too rich). It does this on taxi because it's in the idle state longer. The more it loads up on fuel, the more chances of it shutting down when you do full throttle. Also known as you having a poor transition from idle to full. A well tuned engine should be able to idle for extended time and then shoot up to full throttle without any choking or hesitation.

I usually don't touch the Idle until i have a gallon through the engine, but if it's really bad... just 1/8 or 1/16 turn and lean the idle valve (please refer to your instructions manual to locate this )

Insanemoondoggie

I had the same problem .It acted like it was to rich , but only got worse as I leaned the LSN . Ran fine on run up stand but would bog on take off .

I ended up richening the LSN and the problem went away . Best running 2 stroke I have now .

fcomer84

Hmmm? This sounds familiar! Here is what I had to do to get mine to run right AND most of the time.
1. I am running a TT Pro .46 muffler WITH the baffle in place
2. Disassemble all the nipples and fittings on the engine fuel system and drill
them out to make them larger and to unblock them. Clean everything out carefully.
Do not drill out the needle valve hole!!!
3. If/when I buy another one, I will run 2 gallons of fuel thru it before I try to fly it.
This thing blows black spooge out the exhaust but shows no adverse wear. It just
gets better.
4. Here is the big secret. You will have to run it way rich on the ground. Peak it out and
RICHEN it to loose at least 1,000 rpm. The low speed needle should be about 2 1/2
turns out.
5. My engine is real sensitive to weather changes, even on the same day!
This is a cranky engine and still will quit once in a while, but with an 11x4 MA prop and
10% fuel it will snatch a 5 pound airplane around pretty sporty!
If you are just starting to fly and looking for stick time, put the GMS away for now
and get a Thunder Tiger or an OS.

opjose

Yup, the GMS and the Supertigre's seem to do the same things.

I went throught his with a new ST .61 yesterday, as well as last year with a GMS .76.

Once the engine is fully broken in ( 1-2 gallons of fuel through it ) this seems to be far less problematic.

jetmech43

My Feedback: (9)

the gms suck air try to put hi temp silicone around the carb and back plate

fcomer84

I disagree about sucking air, somewhat. The biggest problem seems to be fuel feed and agressive port timing. Yes, seal the carb. "O" ring anyway and the bar that holds the carb. in place. Mine leaked there worse than at the "O" ring!!??
Oh, did I tell you I put a sealed Boca bearing in the front? Did'nt help!

opjose

Nah, they are actually great engines, especially considering the price.

If they are set up properly, they usually start up right out of the box w/o touching the needles, and after a couple of tanks of fuel are eminently flyable.

Insanemoondoggie

I think it was the first generation .47 that had the air leak problems . Mines a generation III and I think they addressed the problem of air leaks . Mine will fly circles around my O.S .46 ax and uses less fuel . It is a little louder , but it`s a screamer.

opjose

I've had great luck with them.

The only time I've had problems with either the GMS or the T.H. engines were when I played with the needles prior to starting the engine for the first time. Each time I've started them w/o touching anything, out of the box, they fire right up and after a couple of tanks I can tune them.

I notice that the specs ( as far as you can believe advertizing specifications... ) for the T.H. ( also manufactured by the same company ) .46 rates it at 1.8bHP but the GMS .47 slightly less at about 1.6bHP. Yet when you move up to the T.H. .75 versus the GMS .76, the latter has the higher bHP ratingt.

I wonder why the inconsistency?