vertigo72480

Does anybody have any ideas as to why my GMS .47 will not run above half throttle witha standard OS 8 plug in it? I've tried a Fox plug with an idle bar and it runs great. Good transition, and good idle, but with the OS plug it won't run past half throttle. I'm really confused and about had it with the darn thing. Help me, I don't want to buy another engine yet.

matt flyer

My Feedback: (1)

mabey if it is cold where you live the engine will have trouble running. the idle bar stays warm. how dose the uproar fly? what dose the bottom look like? sorry abuot all the questions i know it is your post but i like the uproar.

vertigo72480

check out these threads for info on my uproar http://www.rcuniverse.com/forum/m_25...tm.htm#2504007


http://www.rcuniverse.com/forum/m_24...tm.htm#2495429
I love the plane itself, but I'm really upset with my engine.

I just can't figure out what the heXX is causing this thing to cought an sputter and not run with a normal non idle bar plug.

Harry Lagman

One of the guys at the field was having this difficulty, where his new GMS .47 engine would put the fire out and stop abruptly when transitioning to full throttle. The solution was a fresh glowplug, a tank or two running time and most importantly in this case, new fuel. His fuel was suspect due to age.

Click on this [link=http://www.rcuniverse.com/forum/m_2290854/anchors_2290854/mpage_1/key_gms%252Ctransition/anchor/tm.htm#2290854]GMS Thread[/link] to see more information on tuning the GMS .47.

zx32tt

My Feedback: (9)

It's beeb a while since I owned a GMS.47, but give this a shot. I generally used K&B 1L plugs, no idle bar. Make sure all your fuel lines are snug, and in good shape. The blue silicon stuff has a bad habit of developing hairline cracks and can cause air leaks. My guess is that the engine is way lean or way rich on the main needle. Run the engine as fast as possible and give the fuel line a quick pinch. If it speeds up, its too rich. If it dies, it's too lean. Adjust the hi speed needle first, then work on the lo-end. In general, I found the GMS to be a very good engine, and wouldn't hesitate to own another.
good luck
Z

vertigo72480

I've seen mixed reviews now on the GMS engines. I don't mind wrenching on things but I really just want to fly sometimes too. The fuel lines are all new. With the idle bar plug i could tune the high speed needle all over and find the correct settings. Run it a full throttle, richen it up until it begings to slow down and bog, or go the other way and lean it out until it began to die. My idle bar plug decided it didn't want to ignite and I replaced it with an OS8. No luck then, it wouldn't even rev past half throttle.

My muffler and carb are both GMS replacment parts. The original carb was broken at the same time as the muffler in a crash in my original BUHOR SPAD. Both pieces are GMS parts. I'm thinking about removing the carb again and using some RTV silicon to seal it up in the throttle body on the motor. I'm not sure that's the problem though. I'm also not sure exactly how to tell that it's an air leak. If anyone has any good methods please let me know.

w8ye

My Feedback: (16)

The OS A8 is rather cold. Try a OS A3. They are much hotter.

Enjoy,

Jim

Harry Lagman

It's not going to be an air leak. An air leak would typically manifest itself at low throttle settings.

Some suggestions:

1) Get another idle bar plug like the one you already know works well.

2) Try other plugs as recommended by other posters above. I'd also recommend an OS Type F plug - no idle bar but it is more resistant to flame-outs than many plugs.

3) If you really just want to fly, get a new engine that's made in Japan (OS, Saito, YS, Enya) or Taiwan (Thunder Tiger) and avoid the Chinese stuff entirely.

Bax

My Feedback: (11)

It may not be the glow plug. We run all two-stroke engines with O.S. #8 or #A3 plugs. Never had a problem caused by a good OS plug.

With the GMS .47, you don't say what prop and RPM. We normally prop them so that they'll turn in the hgih 12,000's when leaned to just rich of peak RPM on the ground.

If your engine won't accelerate past 1/2 throttle, we'd suspect that the idle mixture is much too lean. Richen it a LOT, on both idle and high-speed needles, start the engine at part throttle, and then open the throttle to full. Lean the high-speed needle at least to the point where the engine stops breaking back and forth between two- and four-cycle type running. If the engine will take the needle, go ahead and lean to just rich of peak RPM. Now you can adjust the idle mixtures. When you accelerate to full, you may have to keep the glow plug battery attached if the mixture's extremely rich.

We've found that, many times, the modeler tries to adjust the idle mixture first. This is a no-no because you can wind up with the idle needle interfering with high-speed fuel flow. On most model carbs, you need to start out with a rich low-end, adjust the high-end, and then get the low end adjusted.

Use a 10%-15% nitro fuel with at least 18% oil content and containing castor oil as part of the oil package.

Also, many people try to idle too slowly. Accept a few hundred more RPM so that you can get good acceleration. Anything below 2,400 RPM would be considered good. Even if you can get it lower, it may be at the sacrifice of good acceleration.

vertigo72480

well the idle needle and high speed needle are both at rich, very rich. I simply won't go above half throttle. I have a MAS 11x6 on it which is one of the recommended prop sizes. I also have a 10x7 waiting in the wings but I don't really see any need to install it. With the idle bar plug it's a power house, without it a paper weight. I'm currently reading the suggested post above to see if I can glean any information out of it.

vertigo72480

I have noticed that this engine will run with out the exhaust line hooked up to the muffler. That tells me that it's not fuel draw problem. Maybe the OS#8 is just too cold for this engine. One of my Fox idle bar plugs decided it would start working again(it must have been flooded) and I fired it up at the shop where I work for one of the tire techs. With the Fox plug, no problem. It throttles up, transitions, and screams like a banshee. Perhaps I'm just left to running idle bar plugs all the time?

rlbrobst

Mike,
I have a gms .40 and am having the exact same problems! The only difference is that I have a pitts muffler on mine. I found today that Tower recommended the wrong muffler for this motor. If you put your finger over the muffler exhaust partially covering the outlet it would rev up fine and not stall out. So I called them. The muffler that I have does not give enough pressure back to the tank to pressurize the tank due to it having 7/16" tubing for the exhaust as the correct muffler has 3/8" tubing for the exhaust. They told me I could return the muffler but it has already had the tubes cut to fit my corsair. So I would have had to buy a new/correct size muffler. WRONG! Not for another 40 bucks! I am going to slip some copper tubing inside the too large of exhaust tubes and cut the exhaust down a bit. This motor was starving for back pressure. Yours sounds like the muffler you are using is causing yours to starve for back pressure also. You might want to try what I said about partially closing off the exhaust with your finger as someone holds the plane and you run it up to full throttle.

Rick

kyliesgrampa

My Feedback: (42)

I have two GMS 47 engines and have different problems every time I switch them to a different plane. I know you pulled the pressure line and it continued to run, but that does not account for changing throttle. The motors with the smooth muffler do not always supply enough pressure, and this is somewhat dependent on tank location. Some people have added baffles to the muffler inside to solve the problem. I have found simply enlarging the pressure fitting in the muffler with a number 50 drill bit has given a more consistent throttle response in all directions. I also have good luck with morgan fuel, 15%. I do run the # 3 plugs.

RC-Captain

Did you try starting it at full throttle ? I had to do this with my new .28 MAG Then I found the low speed needle was closed . I am convinced every engine runs well , but not every engine breaks in fast.