I have a GMS .25 and it will not kill
even with the throttle closed all the way.
What is up with that? I runs slow enough
to land but with the engine running I'm
breaking props.

Simple: You have an air leak somewhere.

There are many places for air to get in:
1. Around the carburetor barrel
2. Through the front bearing
3. Under the carburetor seat
4. Around the backplate
5. Through the head gasket

What nobody's been able to explain to me is why OS engines and engines with OS carburetors shut down reliably. Even OS engines use shielded (not sealed, not airtight by any stretch of the imagination) front bearings. You'd think that if the front bearings were the problem, OS engines should have major shutdown problems too.

Is the GMS the same as the GM Super 2000 line of engines?
How does it perform? What was break in like?

Spar

I don't think I have an air leak.
No bubbles in the fuel line. I resealed
everything. No change. Thanks, any more
ideas, or how to check where the leak may be?

Sup big bad john, whith the engine running, shoot little amounts of carb cleaner around the flanges of the carb, backplate, hose fittings, ets. if the engine increases in RPMs, you have found your leak, use the little red straw that the carb cleaner comes with, and be sure to only use the smallest amount of spray, but it won't hurt anything.Good Luck, keep us in touch.
Where in Cali are you?

Take the carb off, apply RTV between the carb body and o-ring, also remove the carb screws and seal them up good with RTV and replace them, put the carb back on and press hard, and tighten the screws, that should take care of the air leaks.

RTV is gasket maker available at any auto parts store. You got air coming into the carb, more than likely from the 2 sources listed above, so your engine is getting just enough air and fuel that it doesn't want to shutdown.

There's nothing to think about here. Engines won't run without air, period
If your carb barrel is closing 100% of the way, and it still runs, you have an air leak.

I had a Magnum the same way. I had to re-seal carb, backplate, and needle valve to fix it.

You might give the RTV idea a try. If this is a drawbar type carb holder, you may never
get it to seal with O-rings alone. (Carb or intake may be slightly damaged)

Also, slip a small length of fuel tubing over where the needle valve screws in, so
it's half on the needle, and half on the housing. That will eliminate this common air leak.

Hey John,

1) Did you purchase your engine directly from MECOA?
2) Did they tell you, at the time of purchase, or put anything in the box saying, that the engine would not shut down by design??

They claim they do this to let everyone know about this "feature."

Thanks.

Yes, they (2) came right from MECOA. We fly at Whitter Narrows, about 6-8 miles from MECOA.

No there was no verbal or written notice.

Last weekend, after several club experts helped,
we got one of them to idle and kill. I have
taken everything apart and sealed them when I reassembled it. I added a seal (fuel tube) over the high speed needle. I then turned the needle
out 3 turns and the idle screw 2 turns out. Fired
right up. I (we) adjusted the high speed needle.
It still would not kill. I OPENED the idle screw
about 3/4 of a turn (1/4 at a time) and it kills
from the transmitter. Three weekends of trial and
error, mostly error.

The engines were purchased for slo-quicky 500,
the are speced in the rules. I'm just running some
fuel in them to get them broken in a little.

That's funny, because I believe the AMA Safety Code says you need to be able to shut down the engine by remote control. If the engine doesn't shut down by remote control, no insurance.

You must have a different copy of the code than I do.
Can you post the relevant portions for me? Just curious.
I'm just thinking... a lot of FF, CL, combat, and pylon racers are gonna be tweaked, if so

See other topic on Rule 3.5 Shut down vs GMS.

Sorry, I misunderstood that thread. I thought he was referring to the AMA Safety Code.

According to the rules at http://www.rccombat.com:
Rule 3.3 of the RCCA Open Combat rules states a requirement for engine shutoff.
Rule 3.5 of the RCCA Scale Combat rules states a requirement for engine shutoff.

Of course, it's up to the contest director's discretion whether he wants to enforce that rule or not. If you only have a few competitors at a meet, you really can't afford to be disqualifying people for a minor infraction.

The rule really doesn't make sense, because if you don't have control of the airplane, you almost certainly won't have control to shut off the engine.

The AMA Safety Code does NOT have a requirement for engine shutoff. Of course, if it did, it would have to apply to R/C only. Sorry for the misunderstanding.

I beg to differ. Rule 3.5 of the AMA R/C Combat rules states a clear and unambiguous requirement for Engine Shut Off.

As the the CD's descretion, well, I'm not sure the AMA would agree, given that one of the selling points of our hobby to local communities is the AMA insurance provided, that covers, among other things, incidents at contests. If an engine could not be stopped, and a bystander was injured, then AMA's insurer would not necessarily be obliged to provide coverage. Somehow, I don't think the latitude to wave insurance coverage is really in the hands of the CD, and the insured might think twice if they gave it a thought at all.

If a rule's a rule, then all those engines that won't quite are a problem for everybody. Perhaps GMS should just fix the problem and be done with it. OS engines stop just fine. So what's the deal?

The engine shut off requirement only applies to R/C combat, and is only in the AMA rules because the AMA rules are, for the most part, a verbatim copy of the RCCA rules. It is not part of the core Safety Code, and as such insurance coverage does not depend on compliance with that rule.

GMS is not the only engine manufacturer who has problems with shutdown, but they are the only manufacturer that lauds such a deficiency as a "feature."

As far as forcing GMS to comply, good luck! The number of engines they sell for competition combat is negligible compared to the number they sell for general aviation (including "club combat"). They're heavier and less powerful than most alternatives, and priced about the same as the popular Magnums and Norvels.

How much is a GMS .47 in US? It's about US$40 here in China. Well the OS 46FX is almost US$100 here. So EVERYBODY got a GMS!

Well, I must admit the price is nice. But if it won't shut down, then it may not be allowed in AMA competition - depending on the CD, I guess. That's a lot of latitude, though. Would hate to show up and be disqualified because of my GMS!