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-   -   GMS Engine Tuning Problem (https://www.rcuniverse.com/forum/glow-engines-114/2290854-gms-engine-tuning-problem.html)

Tom Nied 04-24-2016 07:04 PM

I tried that, and it didn't help mine. Maybe I did the mod wrong. Just kept having dead sticks.

Charley 04-26-2016 08:10 AM

Mine doesn't dead-stick. I just couldn't make it 4-cycle. Found out I had a 12x8 APC on it! What was I smokin'? Put on a 11x6 APC. Haven't run it since. Maybe I need to drill out the inlet.

CR

Charley 04-26-2016 10:15 AM


Originally Posted by Tom Nied (Post 12206051)
I tried that, and it didn't help mine. Maybe I did the mod wrong. Just kept having dead sticks.

Could you make it 4-cycle at WOT? If I drilled mine out & it didn't help, I'd look for air leaks. Maybe high temp silicone cement under the carb & on the backplate.

CR

1QwkSport2.5r 04-26-2016 02:36 PM


Originally Posted by Uncas (Post 12206050)
My God this thread is still alive. . . . It seems everyone has since gone electric. I was very frustrated with this engine. Bought it cheap. Found this thread and drilled out the fuel inlet. The engine has run fine ever since. It now pulls my very old Avistar for training missions.

Yeah, I sorta necrobumped this one since I acquired a near new GMS .47. Mine got the fuel inlet mod and will go sloppy rich, but getting good needle settings for a good idle and transition is escaping me. I haven't had time to mess with mine much since I posted here.. Still trying to figure out exactly what needs to me modified to get a good setting. A good idle mixture setting causes the high end and midrange to run lean. It appears the low speed needle either needs to be shorter or re-profiled.

Charley 04-27-2016 01:45 PM

I just took the carb off my .47 to examine it from the bottom & look under the fuel inlet nipple. Took the nipple off ,looked down the hole. The opening in the spray bar doesn't look restricted. The spray bar in my cayb goes all the way across the venturi. There is a rectangular orifice in the middle of it that's pointed down. It's not an "eye" shaped opening such as I'm used to seeing. The end of the low speed needle obstructed that orifice. I concluded that the low speed needle is set too lean; such that fuel flow is restricted at WOT, no matter how far the high speed needle is backed out. So I reset the low speed needle by the "blow through it" method & reinstalled the carb in the engine with high temp silicone cement under it. I hope I can find a happy medium between the needles tomorrow.

CR

geeter 05-10-2016 03:17 PM

I was given a gms.47. One of the worst engines I have ever had. I tried two different carbs , every glow plug there is including idel bar plugs. Still wouldn't run and have been around nitro motors for 25 years. There was a site where people discuss these motors. I was so fed up , I trashed it and so did many other .47 owners.

Tom Nied 05-10-2016 06:45 PM

Same here and I probably have even more years with nitro engines. I sold the two I had on ebxx (you know, the get rid of what you want to get rid of site). They would scream at wot but never could get them to run good through the whole range. Got way too much practice at dead stick landings. Some guys have actually had good results with them. Not me. After messing around with them for over 3 years, I was able to clean them up and sell for half of what I paid. In a word, "perplexing".

opjose 05-10-2016 07:20 PM

If anyone wants to "throw away" any approaching new GMS 47's or Tower Hobbies 46 ( same engine ), send them my way. They have always been great for me.

Charley 05-12-2016 05:05 AM


Originally Posted by opjose (Post 12212309)
If anyone wants to "throw away" any approaching new GMS 47's or Tower Hobbies 46 ( same engine ), send them my way. They have always been great for me.

Ditto; I have a Tower .46 in a Sig Senior. It has always run well. My GMS .47 has always been reliable. I just couldn't get it to 4-stroke last time out.

CR

wcmorrison 05-21-2016 01:57 PM

Those engines were prone to air leaks, at the carb, back plate and probably through the crankshaft at the nose. I never had a problem with Tower Hobbies .46. it was a screamer and I still have it somewhere in my junk pile. The muffler fits right on OS AX/FS series engines and gives them about 500 RPM boost. Unfortunately they are prone to breaking at the front end and nobody made replacements. I have on a FS .46 right now. MECOA was one of the original US sellers of the GMS, Tower Hobbies forced them out. They may have a few parts lying around for the engines. The engines were all made by Sanye. They made a lot of different makes of engines but would go out of business at the drop of a hat. I think they were last makes of Supre Tiger engines, those are gone too.

Mr Cox 05-24-2016 12:10 PM

1 Attachment(s)
I don't know about airleaks, the carb has an o-ring towards the crankcase and the backplate has an o-ring too. There is an oil channel to the front bearing, but that wouldn't make it run too rich I think. The front bearing on my GMS .25 also has dual rubber seals, I'm tempted to remove the rear one.

The liner is a little loose in the crankcase, but I cannot see any leaks on my engine. There is only very little material between the transfer ports in the crankcase and the exhaust port though, so there could be loss of crankcase pressure there.

There is however a real potential problem the way it is delivered with the remote needle setup. There is a plastic plug that sits in the threaded hole where the needle would be in the carb. This plastic plug is too long, and it will obstruct the fuel flow by blocking the access from the fuel nipple. It was a little too difficult to show that in an image, but I've indicated in the picture below how much one will need to shorten plug. With the needle directly on the carb this shouldn't be a problem though.

http://www.rcuniverse.com/forum/atta...mentid=2164106

Cogburn 08-02-2016 11:11 AM

I have a GMS 47 that was mounted on a cheap GP Rapture knockoff. I took it off and fixed the crash damage on the plane(from a flameout). I was going to mount a different engine on it but the mounting hole pattern wasn't the same.

Anyway, I put the engine on my test stand and couldn't get it to run decently other than wide open(black carburetor). In the process of trying to get the spraybar out of the carb I broke the spraybar. I measured the diameter of the carb and rummaged through my engine parts and came up with a square aluminum carburetor off a late 1980's K&B .61.

After turning the spigot down to .511 and shortening it to .340" I installed it and WHOLE DIFFERENT MOTOR. It will idle slowly and throttle up cleanly to 13,800 with a 10x6 MAS(also OS muffler). I could get more rpm but it already has more power than I need. I need reliability and throttle response.

I will be mounting it back on the plane and will be doing some flight testing soon.

Update, since it was on the stand I remounted the GMS muffler(with 1.21" washer in last third of muffler). Peaked it turned 14,580rpm with the 10x6 MAS and still throttled good(way better than the K&B 61 ever did with that carb!).

blw 08-02-2016 12:35 PM

You're right about needing reliability on the GMS.

1QwkSport2.5r 08-02-2016 04:08 PM

The GMS carb has a huge throat in it, which is likely why they screamed so well with their tuned muffler. Mine really honks pretty good, but the geometry of the idle needle and spraybar is a bit of an annoyance. This has been a back burner project due to having other fish to fry lately... But the lowly GMS shouldn't be shamed because of the carb alone. They aren't a barn burner in quality, but for a cheap sport engine, they're not bad. Mine ran fine on an Irvine Jetstream carb, it was just down on power about 1,200rpm or maybe more. The Irvine carb is a fair bit smaller than the GMS is choke-wise.

RC_Fanatic 05-09-2020 02:53 PM

Thanks for a lot of useful information. Found a NIB Tower 46 in a box of other engines I'd acquired over the years. In the box was a "spare" carb body. Recalled there must have been a reason for that so finally found this thread. Somewhere I have a couple of Irvines, a 46 and a 53. Recall they worked well so will probably get them out. Have a few kits I need to to get built and don't want to buy more engines is possible..

RC_Fanatic 05-13-2020 11:35 AM

Looked at the "spare" carb. The hole in the brass part was so offset from the nipple bore that I could only get the very tip of a T-pin into the opening. Almost impossible to blow through the opening. Used the nipple as a guide and carefully opened the hole up to 1.7mm. Stashed it away for later. Also found an idle needle for that engine in the box. Any thoughts about it?

Alexie 07-02-2020 02:54 AM


Originally Posted by Charley (Post 12203001)
Reading this thread got me wondering about the LS needle position so I looked in the carb. The idle bar in my engine goes all the way across the carb throat! I have no Idea how old this engine is. When did they change the carbs? Anyone?

An old post but the mention of the spray bar (idle bar) got me interested because the 47 from the attic that I decided to resurrect recently has the same full width spray bar which is different to pretty well all the engines mentioned in this massive thread. The only other mention was on a larger size engine which seemed to have a different carb to the 47. My 47 was never really run properly from new due to circumstances, just got consigned to storage. so I don't know if it ever ran right at full power for extended runs. I did try and run it a few years back and had all the same problems mentioned here which I've also had during the latest attempt to get it working. This is a Heli version with a nice gold anodized square head, not a version I've heard mentioned before.

If you want to know the age of your engine it's stamped on the engine mounts (least it is on mine), Month and Year with the serial number on the other mount. Mine is Dec 1995 which is interesting because another post stated GMS was setup in 1996. The different carb design on my engine makes you wonder if GMS changed (shortened) the length of the spray bar later in production, perhaps because the full width bar also caused problems ?

My take on this is the low speed needle valve is just poorly designed and manufactured for carefree usage in a hobby engine. You can still see the lathe marks on mine, it's pretty crudely finished. It clearly works most of the time but is too sensitive for easy tuning hence all the problems with fuel restriction at WOT which seems to be the fundamental problem here cured by either reducing flow restriction in the supply nozzle or improving supply pressure from the tank both of which will compensate for the LSN "interfering" at WOT. The issue of the misaligned inlet hole is odd because on mine there is an annulus cut into the brass spray bar insert where the fuel inlet enters and then a hole drilled connecting the annulus to the spray bar tube itself. So it doesn't matter if the hole is aligned with the inlet nipple, the fuel can get to the hole by flowing around the annulus (although for sure it will flow more easily when aligned). As it happens the spray bar can only fit one way on mine because the fuel outlet into the barrel opening (a 2mm long slot half cut into the spray bar) points downward towards the crank and in this position the inlet hole lines up with the fuel nipple position. Maybe on later engines with the shorter spray bar there is no annulus where the fuel enters from the fuel nipple meaning alignment is more important.

As far needle openings are concerned the manual says 1.5 turns for the high speed which never seemed much. Didn't get to check this running because I had the same issue finding the peak as others, the needle was unresponsive. The manual doesn't mention the low speed needle setting but I noted it needs more than 4 turns out just to run at idle and the tip of the needle is just visible in the hole in the spray bar at 6 turns out so maybe this is the position you need to aim for to avoid blocking the outlet hole at WOT.

I was going to give up with this engine after the latest failed attempt but after reading this I might try and fiddle with the LSN setting again and see if it will run reliably. Maybe try re profiling the end of the LSN needle which seems to be too rich at idle and too lean at mid and high end suggesting it's not tapered enough (maybe the lathe marks need removing !). Failing that the heli will be going the electric route.

Tom Nied 07-02-2020 05:28 AM

Good luck. My solution after wasting three years of aggravated flying, numerous dead stick landings, was to get rid of the two I had on ebay. I did get good at dead stick landings.

aspeed 07-02-2020 07:29 AM

A guy in the club has a couple of these .47s and one had worked well for years, and now is giving him problems. Just cutting out when the nose points up. He found that the rubber had disintegrated and was plugging up the flow. He has not tested it yet, but seems sure that is the problem. I am keeping my eye on this because I have a couple .47s and .25s that I might need to use some day. The carb bore seems pretty big for the size of the motor to me. Maybe a bit optimistic for a sport motor? If they are no good, I will try other carbs or make my own for control line combat planes in the .25 size at least. Compare an LA or FP airbleed carb to one of these, much smaller. Dead stick practise is always a good skill to have at any rate. My first RC flights in the early 1980s were with a 2 meter glider and a TD .049, so there was only one try at a landing. I tend to keep my flights over the mowed part of the field as a general rule. No sight seeing tours in most of my planes.

Alexie 07-07-2020 12:44 PM

Managed to get this 47 Heli motor running and it will idle OK and transition fine ...generally. Still seems to have a problem though if left to idle for maybe more than a minute. When you open the throttle quickly, or slowly in fact, it bogs and stumbles and dies. If the glow igniter is still attached it might keep going long enough to pick up then it's fine again and will rev up and down crisply. Lot of smoke whilst it's picking up from prolonged idle so I think it's too rich at idle even though I've leaned the LSN to the point if you go much leaner it stops from lack of fuel (you need to re prime to get it going again). I'm also not convinced the HSN is entirely doing it's thing, seems a little unresponsive. The engine does slow if you richen it but it's not that obvious a transition as I remember on other engines I've run. Possibly also running a bit hot. Also the needle is set at 2.25 turns out whilst the manual states 1.5 turns to start so you'd imagine it should be turned in from there. The LSN ended up at 4.25 turns out which means the tip of the needle is obstructing the spraybar outlet hole somewhat at WOT which may not be a problem if the taper is correct I guess ... if it's correct.

Having said all that this engine was never really run in so maybe that's all it needs. The "manual" says it only requires 15 to 30 minutes of running with no special method which it's possibly had intermittently although perhaps not so much at full power which might be what is required to ultimately make it more reliable.

And all this on 14 year old fuel. Almost tempted to buy some fresh stuff !

the Wasp 07-07-2020 01:19 PM


Originally Posted by Alexie (Post 12616335)
Managed to get this 47 Heli motor running and it will idle OK and transition fine ...generally. Still seems to have a problem though if left to idle for maybe more than a minute. When you open the throttle quickly, or slowly in fact, it bogs and stumbles and dies. If the glow igniter is still attached it might keep going long enough to pick up then it's fine again and will rev up and down crisply. Lot of smoke whilst it's picking up from prolonged idle so I think it's too rich at idle even though I've leaned the LSN to the point if you go much leaner it stops from lack of fuel (you need to re prime to get it going again). I'm also not convinced the HSN is entirely doing it's thing, seems a little unresponsive. The engine does slow if you richen it but it's not that obvious a transition as I remember on other engines I've run. Possibly also running a bit hot. Also the needle is set at 2.25 turns out whilst the manual states 1.5 turns to start so you'd imagine it should be turned in from there. The LSN ended up at 4.25 turns out which means the tip of the needle is obstructing the spraybar outlet hole somewhat at WOT which may not be a problem if the taper is correct I guess ... if it's correct.

Having said all that this engine was never really run in so maybe that's all it needs. The "manual" says it only requires 15 to 30 minutes of running with no special method which it's possibly had intermittently although perhaps not so much at full power which might be what is required to ultimately make it more reliable.

And all this on 14 year old fuel. Almost tempted to buy some fresh stuff !

Alexie,
is this a Ringed engine ?
what Glow plug ?
what Fuel (Nitro% Oil %) ?
what Heli ?
what Muffler ?

Jim

Alexie 07-07-2020 11:51 PM


Originally Posted by the Wasp (Post 12616341)
Alexie,
is this a Ringed engine ?
what Glow plug ?
what Fuel (Nitro% Oil %) ?
what Heli ?
what Muffler ?

Jim


Were any of the engines that are the subject of this thread ringed, the 47 in particular ?
Medium glow plug (Hobby King special)
14 year old 10% Bekra heli fuel
The Heli is a Morley Mavrick (remember them ?) but right now nothing more than a frame acting as a test stand to get the motor running before the head and tail boom are reattached. Just has a head loader in place of the head to create some drive load.
Morley Mavrick custom exhaust, supposedly mildly tuned.

Thanks for the reply

the Wasp 07-08-2020 07:14 PM

I asked you if it was Ringed because I am trying to help you. an ABC engine is very tight, so it may take many runs before it runs correctly.

but first, please, please, get rid of that so called "special" glow plug and buy a quality plug, if you engine takes a short plug buy an OS #7 to start with, because your engine is so new.

another thing, a glow engine, any non E ignition glow engine needs to be loaded correctly for it to run correctly. a prop makes a very good flywheel. but from the photos I have found on the net of the Mavrick's clutch system it looks to be very light. this light clutch gives your engine very little "Flywheel Effect", this, along with running your engine without loading it with blades is good reason for your engine to sputter as you raise the RPM from idle.. a hotter plug will help (specialty with braking in) because a hotter plug will burn more fuel at lower RPM.

14 year old fuel certainly can be questionable good or bad. try fresh fuel.

Jim

Alexie 07-11-2020 09:41 AM

Had another attempt to get this Heli 47 to run and another broken plug (that's the HK specials gone now Jim). However, it did tell me a couple of things

The LSN is probably about right, starts fine and the pinch test results in a slight increase in speed after 3-4 seconds with it starting to die a second or 2 later.
The HSN on the other hand is confusing. If set to the "Manual" setting of 1-1.5 turns out it just doesn't seem right, distinctly lean based on how hot it gets and winding it in further makes no difference other than the engine just cutting due to fuel starvation. Whether this base setting in the manual is a typo or not, who knows. I had it set at 2.5 turns out just to get some sort of drop in revs from leaner settings and it was stumbling like it was rich on transitions so I leaned it back a bit and it ran better but when pulled back to idle after < minute WOT run it idled high with a distinctive ding - ding - ding bouncy sound (bit like a moped). Looking at other stuff on the net this possibly means it was too lean at idle and that probably killed the plug or maybe the plug was damaged by the high speed run at TOO lean a mixture because it ceased to work after this Like I said ... confusing, never a lack of smoke and leaning the HSN doesn't seem to result in an obvious lean point, there is just a slight drop in speed if you wind the HSN open half a turn or more. Also ran it with the LSN set very rich (7 turns out vs 4) to see if it was interfering with the HSN at WOT, managed to get it started and running at WOT but again the HSN didn't obviously hit the lean transition point. Could be part of the problem is the Heli mechanics mask the point at which the HSN goes lean so maybe this needs to be set up on a bench with just a prop so it's able to rev more freely and it's therefore more obvious what the needles are doing.

Plug probably lasted 2 tanks and had a blackish discolouration on one side, coil was bright/greyish but cracked a couple of coils down.

Also pulled the head off and it looked OK other than a scratch in the cylinder wall ... sure that doesn't help and suspect it's from some time ago.

This time it was run with the rotor head on but with blades replaced with head loading tubes and the flybar paddles were turned flat to the direction of rotation which provided possibly too much load but at least it couldn't over rev.

So all out of plugs and no longer convinced this thing is worth saving especially given the way it's eating plugs and the fact the bore is scratched.

I would be interested to know what the ding - ding - ding bouncy sound means though because it's quite distinctive when it does it ... to lean, too rich, overheated ?

the Wasp 07-11-2020 11:53 AM


I would be interested to know what the ding - ding - ding bouncy sound means though because it's quite distinctive when it does it ... to lean, too rich, overheated ?

the last time I heard that type of noise was when I was a newbie and I warped the piston in my first OS 50 when I moved up to 30% nitro and my engine was way too lean. if your engine is shimmed for 0% Nitro you may need to add a shim for 15% Nitro. example> the large Super Tiger's, 23cc and larger will not tune out well at all with over 5% Nitro.
just about the best thing you could do for that engine would be to buy an OS Heli carb for it if one would fit it.


no difference other than the engine just cutting due to fuel starvation.
this could "could" be because the engine is still not loaded correctly. I have seen this on planes too that had props on them that were very much too small for the engines. one of them was a GMS 61 that had a super light wood Zinger 9x4 on it, the engine would start but once up to lift-off speed the engine would stall. after 3 hours of the owner working on it I walked over and saw the 9x4 prop and told him to change the prop. once changed to an APC 12x6 the problem was instantly gone for good.

if you put the engine on a stand and run it with a 10x10, 11x7, 11x8, 12x4, prop on it you may see a well running engine.

Jim


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