HercDoc

It has been 3 weeks now since I have been running my new GMS 47 on my LT-40. I have read every single post here that has any mention of it and have taken all advice necessary to make this thing run reliably. I have sealed both Carb and backplate and have used 4 or 5 different guides to tune it. 3 different instructors at the field have been scratching their head and now the general fealing is it is just pure junk.

Bench tested she runs like a bird and has great throttle response, seem though I cant make it through a full tank without having to adjust it one way or another. Tried different plugs, changed height of fuel tank in relation to carb, changed fuel type 3 different times from 10%-15% with and without castor oil added, changed fuel hoses, and checked tank for air leaks.

I have used rules of thumb for rich lean checks both at idle and high rpm, and have went from 0-1200rpm on the rich side to find something reliable. All seems fine running it static but I can't leave it idle for more than 30 seconds or it will stall on transition to take off throttle. It will run solid at full throttle and will idle on the ground fairly reliably if left alone, but transition to full throttle it seems to be fighting to stay alive from 1/2 to 3/4 throttle.

The list of things I have done to fix it is endless and several other people have had their hands on it. Think I am about to buy a new motor, but it is very frustrating since this is my first everything in the hobby of RC Flight and I have had nothing but grief.

I didn't even make this thread for more advice since I don't think there is much I haven't already done to fix it but I felt that I needed to voice my frustration and if anyone has an opinion they feel they need to share... fill your boots.

The Irony in all this? I am an engine/propulsion technician by trade and maintain and troubleshoot 8000 HP turbo props daily.

Scar

My Feedback: (3)

I hear ya. Mine was about the same, I ran it about 70 flights on my Vmar Extra, gave me fits. I had a .46 FX, stuck it in one weekend, and ran it another 240 flights or so. I'm sure the .46FX would give me the same performance today, if I'd take it down from the garage ceiling.

I had the GMS 47 laying in the garage, figured I'd get around to taking it apart some day, looking at the innards. Never got around to it, don't really know if I could find it today.

Good luck,
Dave Olson

Kmot

My Feedback: (24)

Do you run a fuel filter? It's another source for air leaks, if you haven't checked it yet.

Mitty

If you haven't checked it yet,do you run a little too rich on the low side?

5_spot

My Feedback: (1)

i know what your feeling right now but give it one more chance,adjust the idle so it does idle a little faster,i know you have tried everything but just for the sake ,when you have ir running full throttle on the ground,point the nose towards the sky and see if it still runs without cutting out.
Thats all i have to say on this engine.

bigchap

there is no such thing as a bad engine,some just fuel a little worse than others.

HercDoc

Kmot,
Nope, I dont run a fuel filter.

Mitty,
Idle is adjusted from almost richest setting (where it will not run) and leaned out 1/8 turn at a time so I can remove the glow starter and idle rpm does not change. I have also leaned it out to where it has zero smoke trail 0-3/4 throttle travel. So far my best results found was only a fraction from the factory 1 1/2 turns out.

5_spot,
yes, I adjusted the high end rpm so as to hear slight rpm increase when tilting it 45 degree+ angle. I did not perform this check at low end, as I used the method fore mentioned for adjusting idle & low end rpm. I will also try this. Thx

bigchap,
Your not this first Ive heard say this, and have had individuals tell me they have never had an engine they couldn't tune in 15 minutes, that it was all in the needle valve adjustment. As I would take someone up on this but as I said, it works like a charm on the ground... atleast long enough to look like an idiot when its running right for 5-10 minutes and be told... look theres nothing wrong with it, but I dare ya to strap it to your firewall for a week and come back tell me theres nothing wrong with it.

In conclusion, with a motor that has been well noted for air leaks has failed the QA at the factory level with many unhappy consumers, who is to say that the rest of it is any better. I do know for a fact that there are GMS 47's that run just fine. Just not Mine.

Flyin_High

My Feedback: (1)

Funny thing, I am running the same engine in my plane, and I tuned it, and the thing has run like a charm ever since. And the club president who has been in this hobby for quite a few years swears by this engine.

zetor

My Feedback: (2)

Are you sure?

nicadflyer

You have said a few things that make me think that your engine is running way to rich at idle.

“It will run solid at full throttle and will idle on the ground fairly reliably if left alone, but transition to full throttle it seems to be fighting to stay alive from 1/2 to 3/4 throttle.“

Have you tried to adjust the idle mixture (mid range)?

Try this: Start the engine and adjust main needle for highest RPM, then richen about 1/8 turn.
let the engine idle even if it is fast for 15 seconds. Move the throttle to full speed for 10 seconds. Did it fight to stay alive? Yes, close the idle mixture screw 1/8 turn. Try again.

If the engine dies, then open the idle mixture screw 1/8 turn. This will take some time but you should be able to get a good idle and transition to high end with no hesitation. You will also see a lower idle.

Also you can test for air leaks by closing the idle screw all the way (do not force it) and see if it will idle at a low RPM. If it does, you may have a leak. Good luck. Paul

spokman

My Feedback: (2)

You should contact GMS for technical support. They also make Tower engines. I would think they would be able to fix it for you if necessary.

bhole74

It runs exactly like my tower engine. Put it an a plane you will run at full throttle all the time, only way to fix it.

jettstarblue

1. What prop are you using?
2. How fast are you trying to get it to "transition"?
3. How much time do you have on this engine/is it broken in yet?

Jetts

Bax

My Feedback: (11)

While you may have tried a lot of adjustments, have you tried it this way....

1. Richen idle mixture a LOT.
2. Start at 1/4-1/3 throttle.
3. Advance throttle to full.
4. Lean high-speed needle to just rich of peak RPM.
5. Gradually retard throttle and adjust idle needle. Since you know it's rich, you know you have to lean it.
6. Check idle RPM. You may be trying to idle too slowly. Anything 2,500 RPM or lower is fine.
7. Check acceleration. If it bogs wet, lean the idle a hair and open the idle throttle setting a bit. If it just sags dry, richen the idle a bit.

The engine will break in over the first gallon of fuel or so, and handling should improve as it breaks in.

flycatch

My Feedback: (26)

I have a GMS 1.2 engine and have experienced the same problems you have posted. I will suggest a possible fix to your problem.
Turn the low speed needle valve in until it bottoms out. Backout 2.5 turns. This setting will become your starting point for adjusting the low end. You may want to call this the factory setting.
Go to full throttle addjust for maximum RPM and backoff and 1/8 to 1/4 turn. Now go to the desired low throttle rpm you wish to run. This will depend on the propellor diameter and pitch. Smoothly and slowly advance the throttle. Note how the engine sounds and behaves. If the setting is too rich it will start to hesitate and if it is too lean it will most likely die.
Adjust the low end needle valve to retify these problems. It may work, mine did.

Eyeguy

My Feedback: (1)

Sorry to hear about this bad GMS experience. On my side of the swamp these engines are very popular. Between us we have approx 5 or 6 of these engines in a variety of airplanes. I remember that one was hard to get going reliably at first, but now they are all great. As for the airleak issue, the ones we have here ALL must have leaks because they are hard to shut down will the throttle closed. But in spite of that they scream at full throttle , the transition is great on all of them and they just won't quit at idle. Is the carb clean ? Is all well in the tank plumbing ? Try a different glowplug. Maybe your engine was made late on a Friday afternoon. Contact your engine supplier. As for the Tower Hobbies 46 BB - I have only one - with the rear needle valve, it is mounted inverted in a Tower Voyager and it is a great little powerplant.

ZB50

Why don't you just sell it. I had one and finally gave up on it. Very much like your situation. They make good power, but who the HE*& wants to dead stick all of the time. I say dump it and go with a TT .46pro or Magnum. That's what I did!

ZB

Henry Pel

My Feedback: (7)

I encountered this issue ( unable to shut down at idle with carb closed) with my GMS .47 and came across a message thread that
appears to solve the shutting down problem.
Make sure the carb pinch bolt goes in from the muffler side.
Many had the pinch bolt inserted the opposite side.
This should clear up the non - shutting down issue.
Clockwise tightening of the nut will actually draw the carb barrel into the crankcase hence sealing the oring

Henry Pel

JugMan

I'm sure that this poor SOB is either dead of an anxiety attack, or been sucked into a turbo prop by now (it's been a few years). If he'd ONLY called Tower (GMS) for some tech support,  instead of wasting so much tim e asking "anybody" here online, shame. My GMS .47 motor is absolutely unbelievable. It'll pull a relatively heavy Kaos .40 vertical until I can't see it very well anymore. I've NEVER had a deadstick with this motor. It actually started the first time I hit it with my Sullivan starter, because If followed the simple directions, most likely. I would almost guarantee that the problem came from the low speed needle NOT being in the correct position at the start of all this goofiness. I have personally seen that phenomenon baffle and confuse even the wisest old timer (who assumes that the guy who brought the thing to the field never screwed with it back on the bench at home, a distinct possibility).

jerrysu29

Sell it to one of these guys that say it is a good engine, then go buy a trouble free reliable engine OS! You want quality buy quality. The OS is like a RON POPEEL Rotisserie Set it and Forget it
jerrysu29 Call Sign Wild Man

JugMan

JERRY!  I love my OS .70 Ultimate, and i agree that the OS line is very fine, indeed. I ran a little defense on the OS motor in another forum.  OS is like a little jewel of miniature internal combustion... but more expensive.  With this unfortunate flyer, did you see where he was "new" to the hobby/glow motors? He may have encountered the same issues with any brand of model motor.  Once you stick a screwdriver into that carb there, anything is possible.....

Insanemoondoggie

I started flying with OS engines but after owning a few of the cheaper engines , I sold all my 2OS 46ax engines and replaced them with GMS.47s. They run just so much better and have much more power. I,ll never pay that much money again for an OS. But then , I,m not much on following the crowd.either.

JugMan

Yeah, That's about where I netted out on the whole cost VS fun thing too, Insanomoondoggie.   Some of the cheaper motors don't run "cheaply" they howl.... I've got some expensive motors too, but I seem to get just as much satisfaction, if not more, from the one's that cost less... All except for the "DL50" that  I got from a guy in TX, that wasn't, it turned out, a DL at all, but some other Chinese factory's knock off of the DL50. I guess he was getting a good price on those, huh? Too bad it sold for the same amount as the actual DL. Can you say, "No service at all"?  What I learned from that was that it's more important to know the character of the people you buy stuff from, than what it cost.... whether that be high,  OR low priced merch. Service is key.  Now if you really wanna talk about a JEWEL... check out the Mintor four cylinder gas motor from Italy. WOWIE! It's stunning...to look at. That header! SEXY BEAST!

jerrysu29

JugMan I admit He is new. But as He stated 3 of the club instructors were scratching there head on why they couldn't get it running.
DL? isn't that a Chinese Knock Off of a Quality made US DA?
jerrysu29 Call Sign Wild Man

jeffie8696

Ilook at cheap engines like buying a brand new but un finished house. I will put the time in that the factory didnt and save my money.