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GMS Engine Tuning Problem - 10/27/2004 1:05:52 AM   
Wayne Miller


 

Posts: 977
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi,

I have two 2000 GMS .47 engines. One is older, that I just got, and I also have a new one. The new one has a muffler with fins and works fine. The older one has a muffler with a polished center section and is giving me problems.

I put the older one on a SE and took it to the field today. I'm using 15% fuel with synthetic/castor and the engine has about 1 gallon of fuel through it.

I had a very difficult time adjusting wide open throttle, however the idle adjusted fine and would shut down at low throttle with no problems. Transition from low to high throttle is good. The problem occurred if I left it at wide open throttle - it would all of a sudden stop (no warning) as if I had a fuel blockage, or fuel pressure problem. I noticed it was not over heating (not too lean). I checked tank, fuel lines, clunk, filter and checked needle valve and seat for contamination - all were clear. Also checked for leaks in fuel line, and pressure from muffler - all is OK. I also changed glow plug with same result, but RPM was slightly better.

I found the wide open throttle adjustment was very broad, like one turn either way, and never did seem to really peak. On my new engine the adjustment is very touchy - like two clicks either way.

From reading the posts here at RCU I remember that GMS had an air leak problem. So I returned home, put a new "O" ring on the carburettor then mixed up some soap and water. I plugged all openings on the engine (exhaust, pressure feed, carburettor intake, and fuel intake).

I then sprayed a little soapy water on the engine. Hooked up fuel line to the carburettor intake and blew into it with all the other openings sealed so there was no place for the air to escape.

I could see soapy bubbles (air leaks) at the carburettor retaining bolt as well as a very small amount at the front bearing.

I sealed the carburettor mounting bolt with copper RTV, and also the carb "O" ring for good measure.

I still have a small leak at the front bearing.

I'll see how it runs tomorrow, but I thought I'd check here to see if anyone has any other suggestions, or experince with the same problem.

Thanks for your help,

Wayne Miller
       Post #: 1

RE: GMS Engine Tuning Problem - 10/27/2004 1:43:12 AM   
w8ye



Posts: 17464
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: offline 		Your experience is typical of the GMS 47/ Tower 46/ Hobbico 46 engines.

On a side note, the shiny side muffler doesn't make as much tank pressure as the finned muffler.

Enjoy,

Jim

_____________________________

Attended the CutFinger Institute of DirtNap University for years but never did graduate....

Club Saito Member #7
Original AMA #31261

(in reply to Wayne Miller)
       Post #: 2

RE: GMS Engine Tuning Problem - 10/27/2004 2:13:06 AM   
Wayne Miller


 

Posts: 977
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi w8ye,

Thanks for the information, my assumption is that they must be all made by the same people?

I understand they have a good warrantee, has anyone had any luck sending them back?

Do you know if what I have done should fix the problem?

Thanks,

Wayne MIller

(in reply to w8ye)
       Post #: 3

RE: GMS Engine Tuning Problem - 10/27/2004 2:20:08 AM   
w8ye



Posts: 17464
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: offline 		Try the engine now that you have sealed the carb leak.

If your needle is still insensitive, try switching the mufflers. If it's still not sensitive, try opening up the LS mixture srew a little.

Typically with the shiny sided muffler, the engine will most usually have a rich midrange.

Enjoy,

Jim

_____________________________

Attended the CutFinger Institute of DirtNap University for years but never did graduate....

Club Saito Member #7
Original AMA #31261

(in reply to Wayne Miller)
       Post #: 4

RE: GMS Engine Tuning Problem - 10/27/2004 3:00:02 AM   
Wayne Miller


 

Posts: 977
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Jim,

I should be able to try it tomorrow if there isn't to much rain. I'll let you know what I find.

Fly4Fun,

Wayne

(in reply to w8ye)
       Post #: 5

RE: GMS Engine Tuning Problem - 10/27/2004 3:08:40 AM   
Flyboy Dave



Posts: 13449
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: offline 		If it won't peak up, you have it over-propped. Some engines will complain
about over-propping, by just quitting....with out severe signs of over-heating.

FBD.

_____________________________

An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
"Old Age, and Treachery will overcome youth and skill".
Revver Bro #4.

(in reply to Wayne Miller)
       Post #: 6

RE: GMS Engine Tuning Problem - 10/27/2004 3:38:18 AM   
Wayne Miller


 

Posts: 977
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Flyboy Dave,

Good thought!

I'm using a 12.25 X 3.75 which was recommended to me for this engine/plane combination.

I questioned if this is correct, and if blocking the carb airleaks does not work, I'll try a 10 X 6 or 11 X 4 and see what happens.

Thanks for your help.

Wayne

(in reply to Flyboy Dave)
       Post #: 7

RE: GMS Engine Tuning Problem - 10/27/2004 4:09:08 AM   
Ed_Moorman



Posts: 3683
Joined: 1/5/2002
From: Shalimar, FL, USA
Status: offline 		A 12.25-3.75 should be just fine. I have run that size on mine with no problem. It will not over load or over heat your engine unless there is some problem with your specific engine. I have a GMS, Tower, OS, Magnum, Evo, Thunder Tiger, all in the .46-.52 size and they all run fine on that prop. I use that prop, an APC 12-4, APC 11.5-4 or an 11-6 on all these engines with either 10% or 15% Omega fuel.

The fatter muffler with the shiny center is the "tuned" muffler, usually known as the Tower muffler. They will normally add 700-800 rpm to OS and other engines. The muffler with the fins is the "Standard" muffler. I run one of those because I did not see much difference in rpm on that engine with the tuned muffler, maybe 200 rpm, while the OS & Magnum gained 700-800 over their standard mufflers. The prop I used for the test was a 12.25-3.75 APC.

The tuned muffler has a larger volume than a standard muffler and let the exhaust flow more freely. It does produce less pressure for the tank so you have to tune a little richer for acro planes or expect them to lean out in tight maneuvers. As I recall, the tuning was different from the tuned muffler to the standard when I made my rpm tests, but that is to be expected with tuned exhausts.

_____________________________

Ed Moorman, AMA 553, KD4QBM, Revver Bro #156
R/C Report Magazine, Fun Aerobatics Column

(in reply to Wayne Miller)
       Post #: 8

RE: GMS Engine Tuning Problem - 10/27/2004 4:18:39 AM   
Wayne Miller


 

Posts: 977
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Ed,

Thanks for your input, I'll try a little richer settings as well and see what happens.

I have lots of stuff to try - they are calling for 30% chance of rain, but I still hope to get out.

I'll let you know what happens.

Fly4Fun,

Wayne

(in reply to Ed_Moorman)
       Post #: 9

RE: GMS Engine Tuning Problem - 10/27/2004 4:35:19 AM   
Stiks



Posts: 138
Joined: 4/21/2003
From: GympieQld, AUSTRALIA
Status: offline 		Some of the GMS engines take longer to break in than others. Seen one that would die at full throttle for some time but eventually it went away with a little patience and more time on the motor. Mine runs on 5% nitro and it has the 'tuned' muffler, loves to run on either a bolly 11.5 x 6 or and apc 12x4. The only tuning problem that I have had with mine was using a MA10x6 after it had broken in, the thing just revved it's head off and could not get any decent sort of carb setting from it, many hours of frustration latter we tossed the MA and put the bolly on and not a problem since.

(in reply to Wayne Miller)
       Post #: 10

RE: GMS Engine Tuning Problem - 10/27/2004 5:22:06 AM   
Flyboy Dave



Posts: 13449
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: offline
quote:

ORIGINAL: Wayne Miller

Hi Flyboy Dave,

Good thought!


Wayne.... ....if you get 100 responces, you will get 100 prop/plug/fuel ideas.

Put a 10-8 Master Airscrew on it, or a 10-7 Zinger....and watch what happens.
Forget those 12" props....that engine is a cranker.

FBD.

_____________________________

An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
"Old Age, and Treachery will overcome youth and skill".
Revver Bro #4.

(in reply to Wayne Miller)
       Post #: 11

RE: GMS Engine Tuning Problem - 10/27/2004 9:15:13 AM   
XJet


 

Posts: 3454
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: online 		I just spent the afternoon trouble-shooting a GMS76 (ringed) engine that was behaving very strangely.

After about 2 minutes in the air it would behave as if the throttle were cut back to about 1/2-2/3.

My first thoughts were that it was overheating, but it had done over an hour's running and richening up the needle until it was burbling wouldn't stop it from losing almost 50% of its power. What's more, it didn't have that usual "strained" sound that an overheating engine tends to produce -- but it did have an erratic metalic knocking noise.

We checked the fuel-lines, played around with the mixture, propellor sizes, tried two new plugs, and just about everything else we could think of -- all to no effect.

The guy who owns the engine was using straight 80/20 fuel with Klotz Super Techniplate oil and he tried mixing up a new batch with methanol from a freshly opened brand-new drum -- no different.

Then, when we tried some of *my* fuel, the thing ran like a dream with no signs of any power loss or other problems.

I'm using CoolPower blue (synthetic) that I've blended in a 2:1 mixture with castor oil (making 66% synth, 33% castor) and 10% nitro.

Since he didn't want to toss out the gallon of Klotz-oil fuel he'd just made up, I suggested that he add a few ounces of straight castor and a squirt of nitromethane.

This did the trick. The little bit of additional castor (about 5%) and the small amount of nitro (about 5%) completely changed that engine's performance.

I know that the Klotz SuperTechniplate has a small amount of castor in it -- but obviously it's not enough (for this GMS engine anyway).

The original poster doesn't say how much castor he's running in his fuel but if the engine is relatively new and seems to be sagging, try throwing a few more ounces of straight castor in -- you might be surprised -- I was!

I don't bother buying CoolPower Pink or Klotz SuperTechniplate because I think the levels of castor in them is too low. It's better (IMHO) to buy straight synthetic and add your own castor. This way you can vary the ratio to suit the engine. On my TT42GP I use half castor, half synth, on my TT46GP I use 2/3 synth, 1/3 castor, and on my little norvel I use all castor.

(in reply to Flyboy Dave)
       Post #: 12

RE: GMS Engine Tuning Problem - 10/27/2004 9:29:09 AM   
DarZeelon



Posts: 7084
Joined: 4/9/2003
From: Rosh-Ha'Ayin, ISRAEL
Status: online 		XJet,


Klotz Super Techniplate (KL-200) contains 20% BeNOL Castor oil and 80% KL-100 Techniplate.

You can also get straight BeNOL from Klotz; just degummed Castor (bean) oil.

_____________________________

Dar Zeelon - ISRAEL - ddzeelon@gmail.com
MVVS - Jett - Nelson - Bolly - Mejzlik

(in reply to XJet)
       Post #: 13

RE: GMS Engine Tuning Problem - 10/27/2004 8:38:47 PM   
Ed_Moorman



Posts: 3683
Joined: 1/5/2002
From: Shalimar, FL, USA
Status: offline 		I would say that ringed engines won't break in very easily or quickly on an all-synthetic fuel. The ring doesn't seem to want to seat without some castor in the fuel. After a gallon or so of castor fuel, then the all-synthetic is OK, but I still prefer some castor. I have been known to run high nitro heli fuel in Saitos.

As for the GMS .47 ABC, mine did take longer to break-in than my Mag .52XLS or OS .46AX. it seemed like a gallon before it ran really well. I am running an APC 11.5-4 on it in a light Heckler 3D plane.

_____________________________

Ed Moorman, AMA 553, KD4QBM, Revver Bro #156
R/C Report Magazine, Fun Aerobatics Column

(in reply to DarZeelon)
       Post #: 14

RE: GMS Engine Tuning Problem - 10/28/2004 1:44:10 AM   
Wayne Miller


 

Posts: 977
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi,

I have isolated the problem and I would like to thank everyone for their help. I'll first answer some of the questions asked, and then explain what I did to troubleshoot the problem.

The fuel I am using contains castor and synthetic oil, but I don't know what percentage. It is the Omega Fuel by Morgan and contains 15% nitro. Again, I have 2 GMS .47's with two different mufflers. The engine with the shiny center section muffler with no fins is the problem engine.

Last night I had sealed the carburettor throat leak with copper RTV. I tried the engine today at the flying field with the different suggested props, but I still was not satisfied with the engine performance. As Ed identified in a previous post, the muffler pressure was very low and you could not see any "bubbles" moving to the fuel tank, this means the tank was not being pressurized.

I suspect this is why the "nose up" test before flight caused the engine to go lean, even with the needle set rich.

I was lucky to have lots of interest at the field and one modeler, Merrick, came up with the idea to insert a baffle in the muffler to create a little back pressure. This was made by cutting a 1.25 (1 1/4) inch disk out of the bottom of a soda pop can, and then putting a small hole in the center for the long muffler screw to go through. The inside of the muffler diameter is 1.5 (1 1/4) inch and the exit hole for the exhaust is .25 (1/4) inch. We felt that the .125 (1/8) inch clearance around the baffle would be sufficient. We only used one baffle, and if you reference the picture below, it was the baffle closest to the front of the motor. (Note: