RE: GMS Engine Tuning Problem  
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RE: GMS Engine Tuning Problem - 2/3/2005 7:43:25 AM   
vertigo72480



Posts: 361
Joined: 6/4/2003
From: St. Louis, MO, USA
Status: offline 		I have to say that this thread has been very informative but I don't see whatI'm looking for. Can anybody tell me why my .47 will scream like a banshee with an idle bar pllug but won't run for crap with an OS8? The idle bar plug lets this thing just tear up the sky. When I put the OS8 into the engine it won't go past half throttle. I'm really perturbed to the point of getting rid of it. Problem is, I don' have the cash flow right now and don't really want to buy another motor yet.

_____________________________

Mike in STL.

(in reply to Flyer Freq)
       Post #: 151

RE: GMS Engine Tuning Problem - 2/3/2005 10:30:37 AM   
w8ye



Posts: 17279
Joined: 12/11/2001
From: Taylortown, OH, USA
Status: online 		You've already run this problem through the mill in your own thread. You recieved responses from some very knowledgable people at that time.

It might be time to try some of those suggestions?

You could also take a couple hours and read through this thread?

Here's your own thread....

http://www.rcuniverse.com/forum/GMS_%2547_transition_problem/m_2611432/tm.htm

Enjoy,

Jim

< Message edited by w8ye -- 2/3/2005 11:53:13 AM >

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

Club Saito Member #7
Original AMA #31261

(in reply to vertigo72480)
       Post #: 152

RE: GMS Engine Tuning Problem - 2/3/2005 2:33:49 PM   
Flyer Freq



Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		If you look at the OS plug guide, the OS 8 was designed for .60 size engines and up. Of course, we all know that engines have their own temperment, and we will solve problems, sometimes, by going against recommendations. In this case, however, the OS 8 is the wrong plug. The A3, as mentioned by w8ye in the thread you started, is the way to go. My engine runs great on it, and it might be on its original plug, after 5 years,...not sure though. The OS 8 is definately the wrong heat range.

Andy

< Message edited by Flyer Freq -- 2/3/2005 2:36:17 PM >

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to w8ye)
       Post #: 153

RE: GMS Engine Tuning Problem - 2/3/2005 2:47:26 PM   
Waco Driver



Posts: 158
Joined: 1/16/2003
From: Paris, ON, CANADA
Status: offline 		Here are my findings as promised in my post # 86

As Wayne has indicated in his post # 106, after completely disassembling the engine, we did not find anything mechanical that might cause sudden flameouts. After seeing the annular reservoir formed by the .030" deep by .250" long undercut on the outside diameter of the main jet, and the 2 main jet inlet holes, I discounted the theory that fuel flow restriction caused by misalignment of the main jet inlet holes and the fuel inlet nipple, was the cause of sudden flameouts on this particular engine.

The carb venturi diameter of .312" impressed me as being very large for a sport .47 displacement engine. This is the same size as the venturi used on .60 size engines of a few years back. While this size venturi would give great power at the high rpms turned on a 9" prop, it could certainly affect fuel draw when a 11" or 12" prop was used for aerobatic flying. I therefore made up a venturi restrictor with a .281" inside diameter, the approx diameter of the venturi on my old OS 45 FSR.. I also opened up the muffler pressure tap from .062" to .070".

After thinking about the possible reduction of muffler supplied fuel pressure caused by resriction of the rear mounted main needle valve, I decided to mount the needle on the carb replacing the acorn nut and plastic plug in the end of the main jet. With these mods in place I mounted the engine on my test model which normally has the OS 45 FSR engine installed. The fuel tank is particularly well isolated from vibration and fuel feed has never been a problem in this model.

Last weekend's weather provided a great opportunity to check out the engine. Details are as follows; temp. 28 F, 8" powdered snow; Master Airscrew 11x6 prop; home brew fuel with 5% nitro, 20% oil, 5% acetone; Fox long idlebar 1.5 volt plug; mixture set backed off approx 300 rpm rich from peak .

First takeoff- engine quit abruptly at about 50'. The exact same problem as encountered several times last fall with the engine in the owner's trainer.

I changed the gloplug to a new OS F four stroke plug, reset the mixture as above and took off. Engine ran beautifully during many take offs and landings and aerobatics.

Changed to a new Fox Miracle plug, reset mixture, another engine failure at 50' altitude on T/O.

Changed to an old used Fox idlebar long plug, reset mixture, took off and the engine ran beautifully, equally well as with the OS F plug.

Changed back to original Fox idlebar plug, engine again quit at about 50' altitude.

I removed the GMS and installed my OS 45 FSR and installed the owner's Fox idlebar plug which was giving the engine cuts. I noticed that when removing the igniter current that there was a greater than normal rpm drop but the engine tuned up ok. I did many circuits and aerobatics during 4 flights and suffered no engine cuts. I used the same fuel and prop and the weather was identical to the first day's except that the temperature was 30 F.

My conclusion- Gloplug selection even amongst plugs of the same brand, is very critical with this particular engine, and may well be with many GMS engines . What is particularly disconcerting is the fact that the symptoms exactly match those of an interrupted fuel flow.

_____________________________

MAAC 6273 L

(in reply to Flyer Freq)
       Post #: 154

RE: GMS Engine Tuning Problem - 2/3/2005 2:58:31 PM   
Wayne Miller


 

Posts: 967
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Waco Driver,

Thanks for the very detailed analysis. Your thinking regarding the venturi is the same as Don H out of Brantford, in fact you may both belong to the smae club - you may want to give him a call.

I personally stick with the Fox Idle Bar plug, the price is right, its been around for many years and seems to work in all my engines. The only time I've seen them let me down is if I use them during engine break in - they fail prematurely after that. Typically I'll use an older plug for breakin.

I live in Kitchener, perhaps we'll get a chance to meet and compare notes.

Fly4Fun,

Wayne Miller

(in reply to Waco Driver)
       Post #: 155

RE: GMS Engine Tuning Problem - 2/3/2005 3:14:10 PM   
Waco Driver



Posts: 158
Joined: 1/16/2003
From: Paris, ON, CANADA
Status: offline 		Wayne ...I am Don H out of Paris. Cheers

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MAAC 6273 L

(in reply to Wayne Miller)
       Post #: 156

RE: GMS Engine Tuning Problem - 2/3/2005 4:36:56 PM   
Wayne Miller


 

Posts: 967
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Don,

Sorry, I failed to connect your RCU name to you. Again, thanks for your input and for all the things you've shown me, and the help you've given to others in getting started in the hobby.

Fly4Fun,

Wayne

(in reply to Waco Driver)
       Post #: 157

RE: GMS Engine Tuning Problem - 2/6/2005 1:04:15 AM   
Flyer Freq



Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		Hey guy's, go back to entry 109. My theory on the hole missalignment appears to be correct. We had temperatures today of 47 degree's F, so off to the field I went. With the warmer temperatures, the engine ran like a top. Transitions were snappy, in fact, that may be an understatement. Due to ground clearance, I could only run my APC 11X3. It turned it consistantly at 15,700 and at times saw as high as 16,200 rpm. In fact, on my second flight, I blew the element on the A3 glow plug. I put another plug in, and was back off to the races. The regular summer crowd was at the field, except for the engines owner. No one could believe it was the same engine, as before I replaced the spray bar, you were lucky to get the engine off the ground. Fortunately my witnesses will vouch for its incredible performance. I am confident that if everyone gets a new carb body with the hole in the spray bar, their problems will go away. I must add, that the engine was very easy to set. No putzing was required!

I am dissappointed, however, that MECOA has neglected to return my e-mail as to our issues.

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)
       Post #: 158

RE: GMS Engine Tuning Problem - 2/6/2005 1:49:38 AM   
Wayne Miller


 

Posts: 967
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Andy,

I went back and read 109, and I understand your analysis led you to believe fuel turbulance at the brass intake hole may have been the problem.

Your last post said to order a new brass insert to solve the problem. I'm not quite sure why the new brass insert will fix the problem.

Originally I stated I drilled both the intake and exhaust nipple and the brass insert to get mine working. I suspect it was the drilling of the brass insert hole larger was the fix for yours, but I'm not quite sure. Can you explain what you think the fix is?

I'm glad to hear the engine is working well, congratulations, your hard work paid off!

Fly4Fun,

Wayne

(in reply to Flyer Freq)
       Post #: 159

RE: GMS Engine Tuning Problem - 2/7/2005 4:26:01 AM   
Flyer Freq



Posts: 906
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline 		Hi Wayne:

Unfortunately, to get the brass insert, you have to get the whole carb body. Fortunately that is only 8 or $9.00. I put the brass insert (spray bar) from my good engine into the carb of the engine that was not running right. When I first tested it like this, it would not transition well in vertical flight. I had wondered if it was due to the below freezing temperatures, as a friend with a new O.S. .46 AX was having the same problem in the cold. Since in full throttle, vertical flight, the engine ran well, the only way I would know if the difficulty in a hover was a real problem, was to fly in temperatures above freezing. The 47 degree weather was perfect for that, and it proved the spray bar to be the correct fix.

No drilling was done on this spray bar at all. The hole was just spaced further away from the needle valve. I believe I listed the rough distance from the hole to the shoulder of the insert in another entry, but in simplest terms, it was more centered on the nipple. Looking at the port where the nipple screws in, the entire whole in the insert can be seen, rather than just the edge. The undercut is irrelevant. While it is helpful at lower rpm, at higher RPM, the flow is so fast, it can't make that sharp turn, from the end of the nipple to the hole in the insert, without turbulance impeading the flow. I believe that the fuel may not be entering the spray bar on the taper of the needle either, though I haven't tried to measure that. If the fuel is entering on the flat of the needle, or even on the transition from the flat of the needle to the taper, I believe the adjustments would be very touchy, if not impossible.

I hope I cleared that up, if not, let me know and I will try to write it another way.

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)
       Post #: 160

RE: GMS Engine Tuning Problem - 2/7/2005 2:01:52 PM   
Wayne Miller


 

Posts: 967
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Andy,

You did a great job of explaining it, thanks. We may have done the same thing when we drilled out the brass insert, and this centering the hole.

Thanks for all your help.

Fly4Fun,

Wayne

(in reply to Flyer Freq)
       Post #: 161

RE: GMS Engine Tuning Problem - 2/7/2005 11:34:44 PM   
yoyo27983


 

Posts: 8
Joined: 1/14/2005
From: , NC, USA
Status: offline 		Well, After drilling my muffler nipple and the remote nipples and the carb nippleon my new GMS .47, I did not see any difference in the way it ran or died I should say. BUT, I took the end cap out of the carb and looked thru the spray bar hole and saw some trash in the spraybar from where I had drilled it I guess. cleaned out the trash, reassembled, re-tuned and now it runs better than it has yet! I have a run little over a gallon of 15% tower hobbie fuel in it, and it runs better with every flight. I am still tweaking it as it wants to flood out if run at a lower speed too long, and it has to have the fuel blown out after a taxi and just before take off or it will die at 10 feet. But I am much happier now. I am just learning how to fly and a first timer doesn't need this, he needs stick time!

(in reply to Wayne Miller)
       Post #: 162

RE: GMS Engine Tuning Problem - 2/7/2005 11:54:15 PM   
Wayne Miller


 

Posts: 967
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline 		Hi Yoyo27983


I'm glad to hear you got yours running, that's another one "off the shelf" and in the air.

If the plug is being flooded at low RPM, you may want to tweak the low end needle just a very small amount, like 1/16 of a turn from where it currently is (it may go either way, in or out). Another fix is to try a Fox Idle bar plug. It may also need just a little more break in - these engines are very tight.

Thanks for keeping us up to date.

Fly4Fun,

Wayne Miller

(in reply to yoyo27983)
       Post #: 163

RE: GMS Engine Tuning Problem - 2/9/2005 1:06:02 AM