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problem with my GMS 1.20

Old 09-11-2005, 12:20 AM
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gnirwin
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Default problem with my GMS 1.20

I have a new GMS 1.2 that was properly broken in and mounted on a Funtana 90. I put a OS F glowplug in it and the engine ran very well, no hesitation in the midrange , very nice. After about 20 flights the pitts muffler came loose and I flamed out and landed the plane (hard) but safely with no apparent damage. I re-installed the muffler with the gasket, Loctited the bolts, and flew the plane again today but with problems. The engine would not stay running. I changed to a new OS #8 plug, that didn't help. I rechecked the High speed needle and RPM's with my Tac, they were OK. I checked all my fuel lines and there appeared to be no air leaks. When I originally mounted the engine on the plane I put high temp sealant under the carb so I don't think I'm leaking there and that it was a problem. i'm going to check the tank klunk tomorrow. Does anyone have any other Idea's what it could be. One more thing is that I switched from 15% nitro to 10% on the flight that I lost the muffler. Also today the plane would fly for about 2 to 3 minutes then die. If I inverted, it would die even sooner. Many dead stick landings.
Old 09-12-2005, 11:28 AM
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bob27s
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Default RE: problem with my GMS 1.20

check the fuel system. Chances are your crash screwed up something inside the tank. Cut clunk line or folded clunk line.

Any time you have an engine that is running well, then suddenly is not after an incident - check the fuel system completely.

Stick with the F plug. OS#8 is too cold for that engine.

Depending on your crash, you may have gotten dirt in the front bearing, and if it hit hard enough, you may have a bent crankshaft.

Check the fuel system first.
Old 09-12-2005, 04:35 PM
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Bax
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Default RE: problem with my GMS 1.20

When the muffler came off the engine, it had to have done so somewhat gradually, as the bolts worked loose. This would have cause a reduction in pressure to the fuel tank, which would cause leaning. When the muffler finally came off, there wasn't enough fuel pressure to feed the engine and it quit. Your engine may have been damaged by an overheat.

Of course, the only consequence could be the glow plug. Put a Type F plug back in and see how it goes.
Old 09-14-2005, 05:42 PM
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gnirwin
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Default RE: problem with my GMS 1.20

The hard landing was not a crash. It was a hard landing, a little faster and steeper than normal. I appreciate the responses but there is a little history to the engine. A fellow club member bought the engine new and broke it in but never got the engine to run correctly in the midrange. After several dead sticks I bought it and the plane it was mounted on from him. After a few tanks of gas and a different plug I got the engine running properly, and like I said it ran great up till the muffler came loose. Now it is running just like it did when I got it (I put a new glow plug in it and I got it running again to what appeared normal) the engine stopping after about 3 minutes of flight. I have a Perry pump I am going to install on the plane. I have read of others that have this engine and who have had midrange problems with the carb. If someone could tell me if a pump corrected the problem I would appreciate it. I'm about ready to give up on the engine alltogether.
I understand that I could have damaged the engine with the muffler coming loose but the engine makes no noise and idles very nicely until I get it into the air. I have lost other mufflers in the past with no damage to engines but I guess there always is a first time for everything. Heck, the muffler could have been a lttle loose when I got it making for all the readjustments after I reattached the muffler.
Maybe the only reason it was running right for me was because the muffler was loose and it leaned the engine out in the mid range.
Old 09-14-2005, 08:20 PM
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Azcat59
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Default RE: problem with my GMS 1.20

I wonder if your "sudden arrival" may have forced the klunk into the front of the tank, pinching off your fuel supply.

I also think that the mid-range on most two cycles is usually somewhat rich (which is why OS developed a three stage carb), and most of them run better either full out or at idle.

I would pull the tank out and give it a good check out first.

Clair
Old 09-14-2005, 10:30 PM
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gnirwin
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Default RE: problem with my GMS 1.20

I did pull the tank, everything is good. I really have gone over this engine and the plane. I guess I may never know. I'm pulling the engine out of the plane and replacing with an OS. I may try to bench run the engine down the road sometime to try to figure it out. Right now I have a very nice plane that I don't want to get destroyed because I can't get this engine running correctly. This engine has not only frustrated me but it frustrated the guy that I bought it from.
Old 09-18-2005, 04:50 PM
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coronabob
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Default RE: problem with my GMS 1.20

I decided to modify the GMS 1.20 carb to hopefully (?) get rid of the fat mid range. I disassembled the carb completely. The only difficult part was to drive the metering valve out of its pressed fit in the carb body. I did this by placing a popsicle stick over the end of the threaded collar where the high speed needle screws onto and tapped it out with a small hammer.

I widened the rectangular slot in the fuel metering valve from its original 0.05" to 0.065" - widened towards the idle needle. I simply used some hand files. I wrapped the screwdriver end of the idle needle with two layers of blue masking tape and chucked it in my power drill. I blackened approximately 0.065" from the tip to guide myself and started to run my drill by pressing it flat on my work bench. I held a file at an angle and started working the tip nice and slow until I got a nice concave (kinda sorta) taper approximately 0.065" from the tip. I left the tip blunt approx. 0.5mm like mechanical pencil lead. I deburred the metering valve to make sure the idle needle slips in and out nicely in the valve and its new widened slot. I reassembled the carb by placing a small drive socket over the meter valve and drove it back into the carb body. The rest of the assembly was straight forward. I checked to make sure that I got no obstruction from completely shut to wide open throttle as before.

I ran my GMS 1.20 with its modified carb on my test stand. I estimated that the fat mid range was now reduced to an acceptable level. The engine did not stumble and died when transitioned from 1/4 up. I left it running for a few minutes at different high idles: 1/4, 1/3 etc. Upon opening it up to WOT, it responed semi fine, i.e., some smoke trail but it did not sputter and died at any point. It transistioned very nicely in the vertical position - indicating that the mid range is still somewhat 'fat'.

I will have to test fly it to see if this mod holds out. I did find that the needle tweaking, or lack of it, was nowhere near as sensitive it was originally. It is too nice of an engine to get rid of: super easy to start, nice reliable idle, very low fuel consumption, and a beautiful gold anodized head. We'll see!
Old 09-19-2005, 12:44 AM
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buenger_2000
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Default RE: problem with my GMS 1.20

I have a GMS 1.20 in my Funtana as well. I'm tired of messing with this thing and my attempt to return it to Tower Hobbies was unsuccessful. First thing, I ran it and broke it in in the aircraft on the ground per instructions. Ran well after first tank low to mid. Second tank ran great....high was great...

Well, took aircraft to the field and started right up
had friend hold upright and invirted ran great
taxied out and wentto throttle up it Died!
dit it over and over
finally got it in the air and it dead sticked
tore off landing gear....tried perry pump and that didn't work

what do you guys recommend...can't get it to run right and I'm considering a perry carb..let me know...thanks
Old 09-19-2005, 10:26 AM
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gnirwin
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Default RE: problem with my GMS 1.20

You could do what I did. Yank it out of the plane and replace it with a OS 1.60. My gear were ripped off 2 times. I really beefed this area up and have had some hard landings since and the gear have stayed on but this shouldn't be an issue any more with the new engine.
Old 09-19-2005, 10:57 AM
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Default RE: problem with my GMS 1.20

So you just got sick of it...lol....well I don't have the kind of money to spend...I epoxied the fire wall so it will be hard to put in a new engine mount...or did you use the same mount....of course we had to modify the mount to fit the 1.20....I really want to figure out how to make this biatch run good~~!!! I've had this plane for almost 5 months and havn't had a successful flight yet!!!
Old 09-22-2005, 09:33 PM
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gplarry
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Default RE: problem with my GMS 1.20

Buenger,

Try an OS type F glow plug in your GMS.

The 120 likes them.

Once the plug is installed richen the low needle a good bit.

Experiment by leaning the low needle a bit at a time to find the right spot with good idle and transition.



Old 09-25-2005, 03:39 PM
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Robert 8310
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Default RE: problem with my GMS 1.20

I have had the GMS 120 for about two months now and I as many have indicated resourted to the OS "F" plug. However, I have found that even these plugs will not provide sucessful operations for more than several flights before I am seeing dead sticks again. This becomes very expensive and not a good solution. I am not fully sure but I think my engine is losing compression as well. I thought my problems were just an isolated bad engine but after reading several other accounts just like mine I am not so sure.
Old 09-25-2005, 07:36 PM
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smosher9
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Default RE: problem with my GMS 1.20

I have GMS's a 40 and a 47, both stumbled right out of the box. I have found that there
is a very small range on the low speed mixture where the engine will operate well.
Anymore than a very small adjustment either way will either cause it to stumble and spit fuel or die completely. To find the sweet spot I set the high speed mix by tach, dropped the throttle and adjusted the low speed mix, go back and adjust the high speed mix. Let it run at idle for awhile and see what happens when I give it WOT. If it dies then its lean, if it coughs and spits fuel then its rich, make very small adjustsments and keep adjusting the high speed mix every time you adjust the low speed. Enventually you will find the best setting. I marked the low speed on the throttle body. On the 47 with a apc 11x6 prop max rpm is 12200. I set the high speed mix to 11600. The low end tach's out at 2300. I use 10% CM.

Steve
Old 09-25-2005, 11:25 PM
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buenger_2000
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Default RE: problem with my GMS 1.20

Well, My wife and I recently moved and I've been outta my planes for a couple months but am settled in now. Was working on the GMS 1.20 cleaning it today and went through the whole thing. I did notice today that there is a leak coming from the bolt hole that holds the carb on...could this cause some probs? What do you guys think. Tomorrow I'm going to get some silicone and seal that puppy up...
Old 09-26-2005, 08:35 PM
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gplarry
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Default RE: problem with my GMS 1.20

I have read several posts that talk about air leaks around the GMS carbs.

An air leak would cause you to have to set the low needle somewhat rich to compensate for the extra air.

The rich idle setting would translate into a rich midrange.

I have also read several posts that say that once the engine is properly sealed and broken in it runs great.

I am curious about how well these engines last.

Has anyone had one a long time - like hundreds of flights?

How is it holding up?




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