GMS Engine problem
04-30-2005 | 04:56 PM
#1
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From: Pueblo West, CO
GMS Engine problem
I have a GMS .47 and I cannot seem to get needle valve set I have flown plane 15 times engine leans out in are and dies. I have ran 3 tanks of fuel through it I bought from tower hobbies. I have tried all kinds of plugs fuel. It will run fine on the ground but not in the air it takes like 3 turns to richen it up enough to fly it a little longer and then it seems to over heat and die do you think it is the hole in the needle valve not beeing aligned. Please help me with this.
04-30-2005 | 08:46 PM
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From: Mary Esther, Florida, FL
RE: GMS Engine problem
Ready:
Th biggest problem we've had with GMS has been trash in the fuel system, ranging from bits left inside the carb to trash in brand new tanks. Once everything has been cleaned they've run very well with no more problems.
Bill.
Th biggest problem we've had with GMS has been trash in the fuel system, ranging from bits left inside the carb to trash in brand new tanks. Once everything has been cleaned they've run very well with no more problems.
Bill.
11-05-2005 | 06:57 PM
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From: Smithfield,
NC
RE: GMS Engine problem
Been having the same problem with my GMS 61. Get the needle valve set and the engines does fine on the grond, but once in the air it dies on me after about 2 laps of the air field. I have it on a GP stuka, so it is a cowled engine, but tomorrow I am gonna try flying without the cowl to see if it is a overheating issue or not. Any other suggestions?
11-05-2005 | 07:53 PM
#4
My Feedback: (1)
RE: GMS Engine problem
I have a couple of GMS .47s in a twin that are now running fine.
-My GMSs took at least a half gallon to run smoothly. One of them took a gallon of fuel through it.
-Turn your low end needle out a half turn to make sure you don't have it so far in, the top end won't adjust, then try it.
-Don't worry about a good low idle until you have a lot more fuel through the engine.
-I had some trouble with the remote needle, so all mine, .47s and .32s, now have the front needle. You might try moving the needle to the front (I am assuming you bought the remote verstion) and giving this a try.
-Even if you don't move the needle, unscrew the whole needle valve assembly from the rear mount or the carb and blow out the area. I had some black gunk in mine and blamed the engine until I checked.
-Check your tank location. It should be vertically located where the center of the tank is even with, or a little lower than, the fuel jet in the carb. Having it lower than this will cause leaning out in the air.
-My GMSs took at least a half gallon to run smoothly. One of them took a gallon of fuel through it.
-Turn your low end needle out a half turn to make sure you don't have it so far in, the top end won't adjust, then try it.
-Don't worry about a good low idle until you have a lot more fuel through the engine.
-I had some trouble with the remote needle, so all mine, .47s and .32s, now have the front needle. You might try moving the needle to the front (I am assuming you bought the remote verstion) and giving this a try.
-Even if you don't move the needle, unscrew the whole needle valve assembly from the rear mount or the carb and blow out the area. I had some black gunk in mine and blamed the engine until I checked.
-Check your tank location. It should be vertically located where the center of the tank is even with, or a little lower than, the fuel jet in the carb. Having it lower than this will cause leaning out in the air.
11-05-2005 | 11:03 PM
#5
Senior Member
My Feedback: (14)
RE: GMS Engine problem
ORIGINAL: ready440
I have a GMS .47 and I cannot seem to get needle valve set I have flown plane 15 times engine leans out in are and dies. I have ran 3 tanks of fuel through it I bought from tower hobbies. I have tried all kinds of plugs fuel. It will run fine on the ground but not in the air it takes like 3 turns to richen it up enough to fly it a little longer and then it seems to over heat and die do you think it is the hole in the needle valve not beeing aligned. Please help me with this.
I have a GMS .47 and I cannot seem to get needle valve set I have flown plane 15 times engine leans out in are and dies. I have ran 3 tanks of fuel through it I bought from tower hobbies. I have tried all kinds of plugs fuel. It will run fine on the ground but not in the air it takes like 3 turns to richen it up enough to fly it a little longer and then it seems to over heat and die do you think it is the hole in the needle valve not beeing aligned. Please help me with this.
Whenever someone says what you have said, I know that there are really only two kinds of problems involved, if you have done as Will Robison has stated and have checked for debris in the carb and ensured that the fuel system is up to snuff.
An engine does not "know" the difference between bench running/ground running/flying in the air. Since it is not conscious and it is not aware of your intentions, there is no reason to assume that it is punishing you by not running right. You did not say such a thing, but I think that our emotions, as human beings, sometimes makes us feel this way, even though our intellectual/cognitive mind knows otherwise. So what's the point? Don't become frustrated and revert to your emotions for decision making. Let's think this thing through.
What changes when the model is in the air? For one thing, it unloads. Unloading means that the engine requires LESS fuel to run properly. As the fuel burns off, fuel draw drops, so leaving the ground slightly rich is a great idea, lest we end up running lean toward the end of the tank. So, the first possible cause is getting off too lean.
The second possible cause is fuel foaming. This one is as serious as a heart attack and is probably responsible for at least 75% of the posts that I see which refer to the engine quitting in flight.
The model sitting on the ground with the engine running and the model in the air with the engine running are two completely different creatures. Many times, in fact, the vast majority of times, the engine will run normally and the fuel will not foam with the model on the ground (or field stand). The fact that it is touching something solid changes the mechanical resonant frequency of the model, for lack of a better, engineering/more precise term. Once the model is "on the wing", this mechanical frequency changes. The latter is when fuel foaming usually occurs and throws the engine carb settings out of kilter.
One way to check for fuel foaming "on the wing" is to have the model running with a friend holding each wing tip and supporting the model up off of the ground. Go through the various rpm ranges and hesitate at the changed rpm for a while. Give the bubbles a chance to move up the fuel line and into the engine. Ah-ha! The engine leaned out or quit. What now?
You have to ensure that no part of the fuel tank, including the neck and brass fuel lines, are touching any solid part of the model. This includes the fuel tank neck passing through the firewall, or those funky firewall tank supports that are included in some ARFs. Yes, I do know better than the manufacturer in this instance. Their obligation is to their company, not to you. They do not care if your engine runs bad. After all, it was your crappy engine that crashed their wonderful model. Get it? <G>
The model's fuel tank needs to be supported by soft, uncompressed, foam rubber and must be completely prevented from touching any part of the model. This is a real PITA, isn't it? Sure is, but that is the way that it is.
I know, I know. You know so and so and his model has the fuel tank neck feeding through the firewall. He doesn't have any problems, so I must be wrong. Right? Wrong. He just got lucky. Even a stopped clock is right twice a day.
11-06-2005 | 01:45 AM
#7
My Feedback: (21)
RE: GMS Engine problem
Remove the fuel inlet nipple on the carb and see if the fuel passage was
miss-drilled like this one on my GMS .47.
If it is like mine, it is easy to redrill and open the restriction. Also....use a piece of
fuel line....connect it to the muffler pressure nipple that goes to the tank. Blow through
it, and make sure the nipple is not restricted into the muffler. Some of these were
not drilled correctly, and did not allow enough pressure to the tank. This and the
carb inlet nipple restriction were the cause of the problems.
FBD.
miss-drilled like this one on my GMS .47.
If it is like mine, it is easy to redrill and open the restriction. Also....use a piece of
fuel line....connect it to the muffler pressure nipple that goes to the tank. Blow through
it, and make sure the nipple is not restricted into the muffler. Some of these were
not drilled correctly, and did not allow enough pressure to the tank. This and the
carb inlet nipple restriction were the cause of the problems.
FBD.
11-06-2005 | 02:33 AM
#8
RE: GMS Engine problem
I think that experience should be read seriously below.Main thread is at:http://www.rcuniverse.com/forum/m_22...page_13/tm.htm post No:303
ORIGINAL: JDW
Hi,
I recently found a totally unexpected fix to problems I was having with a GMS .47 fitted with a Tower muffler and running a 12.25 x 3.75 APC prop in a 3D model.
The problem was that, even though the engine started easily, idled reliably, transitioned OK and had reasonable power (12,000+ rpm) in horizontal flight, it would sag as if lean when vertical.
The only way to achieve sustained vertical flight was to tune it with the model vetical. This involved opening the main needle an ADDITIONAL 3 turns (i.e. 6+ turns open!!). The engine still started, idled and transitioned OK but was way down on power at full throttle (only 11,000 rpm). It also smoked like crazy when vertical but would sag and die if the needle was closed even a couple of clicks.
This looked like a fuel supply or muffler pressure problem so I did all the appropriate things (many previously mentioned in this thread).
I removed and pressure tested the tank, replaced all the fuel tubing, removed the fuel filter, stripped and cleaned the carb, drilled out the pressure nipple, sealed the carb to the crankcase, replaced the glow plug etc etc.
NONE OF THIS MADE ANY DIFFERENCE WHATSOEVER TO THE PROBLEM!
In desperation and because there was nothing else left to try, I leaned the IDLE needle 1/4 turn (despite the fact that it had already been set apparantly correctly by the pinch test method at break in and the engine idle was already slow and very reliable)
The effect was immediate and dramatic. I was able to LEAN the main needle one full turn. I leaned the idle needle another 1/4 turn and, again, was able to lean the main needle another turn. After a few more cycles of this and with some final fine-tuning I had the engine pulling 12,600 rpm horizontal and vertical, transitioning beautifully with a reliable idle at just under 1,600 rpm.
I refitted the fuel filter and even an 'undrilled' pressure nipple and went flying. In the last couple of months I logged many flights with no problems at all - I haven't had to touch either needle and the engine has never hesitated or even coughed. It is now transformed into a very powerful, reliable, user friendly, 'happy' little 2 stroke.
Remember that all I did to totally transform the FULL THROTTLE performance was to lean the IDLE needle!!!
"That's only one engine - it probably had a bit of dirt in the carb that finally moved --" I hear you say.
NOT SO - Not only is the problem reproducible on my engine if I open the idle needle a turn or so, I have also resurrected another GMS 47 (also fitted with a Tower muffler) that was discarded by anothewr club member as being too unreliable - it kept 'leaning' in flight and stopping. This engine is also now running like a clock. A third near new 47 was also improved considerably by getting the idle needle correct instead of APPARENTLY correct.
So why does the idle needle position dramatically effect the full throttle performance?
A friend (and fellow engine 'nut') and I believe we may have the answer. We think it has to do with venturi effect and fuel atomization.
If you look down the throat of the carb (in the full throttle position) you will see that the idle needle is retracted just clear of the end of the spray bar tube. In the three engines we have 'sorted' recently, the gap between the end of the needle and the end of the tube is about .002" to .003" when correctly tuned. Remember that it is poissible to get a good idle and transition with the idle needle much richer than this - i.e. a much larger gap, but this seems to result in poor and unreliable full throttle performance.
We think that this is probably because the venturi effect at the end of the spray bar tube is compromised if the gap is greater than a few thou. This, in turn, results in less fuel 'draw' which, of course, "looks' like a lack of of tank pressure. We believe it also reduces the atomization of the fuel so that the engine 'acts' lean even while it's smoking.
So, forget about drilling out pressure nipples, changing tank positions, sealing carbs etc at least for a while - It's all too hard and, on my engine at least achieved nothing. Try checking that idle needle to spray bar tube end clearance and working from there to see if that solves the problems.
Good luck,
John.
Hi,
I recently found a totally unexpected fix to problems I was having with a GMS .47 fitted with a Tower muffler and running a 12.25 x 3.75 APC prop in a 3D model.
The problem was that, even though the engine started easily, idled reliably, transitioned OK and had reasonable power (12,000+ rpm) in horizontal flight, it would sag as if lean when vertical.
The only way to achieve sustained vertical flight was to tune it with the model vetical. This involved opening the main needle an ADDITIONAL 3 turns (i.e. 6+ turns open!!). The engine still started, idled and transitioned OK but was way down on power at full throttle (only 11,000 rpm). It also smoked like crazy when vertical but would sag and die if the needle was closed even a couple of clicks.
This looked like a fuel supply or muffler pressure problem so I did all the appropriate things (many previously mentioned in this thread).
I removed and pressure tested the tank, replaced all the fuel tubing, removed the fuel filter, stripped and cleaned the carb, drilled out the pressure nipple, sealed the carb to the crankcase, replaced the glow plug etc etc.
NONE OF THIS MADE ANY DIFFERENCE WHATSOEVER TO THE PROBLEM!
In desperation and because there was nothing else left to try, I leaned the IDLE needle 1/4 turn (despite the fact that it had already been set apparantly correctly by the pinch test method at break in and the engine idle was already slow and very reliable)
The effect was immediate and dramatic. I was able to LEAN the main needle one full turn. I leaned the idle needle another 1/4 turn and, again, was able to lean the main needle another turn. After a few more cycles of this and with some final fine-tuning I had the engine pulling 12,600 rpm horizontal and vertical, transitioning beautifully with a reliable idle at just under 1,600 rpm.
I refitted the fuel filter and even an 'undrilled' pressure nipple and went flying. In the last couple of months I logged many flights with no problems at all - I haven't had to touch either needle and the engine has never hesitated or even coughed. It is now transformed into a very powerful, reliable, user friendly, 'happy' little 2 stroke.
Remember that all I did to totally transform the FULL THROTTLE performance was to lean the IDLE needle!!!
"That's only one engine - it probably had a bit of dirt in the carb that finally moved --" I hear you say.
NOT SO - Not only is the problem reproducible on my engine if I open the idle needle a turn or so, I have also resurrected another GMS 47 (also fitted with a Tower muffler) that was discarded by anothewr club member as being too unreliable - it kept 'leaning' in flight and stopping. This engine is also now running like a clock. A third near new 47 was also improved considerably by getting the idle needle correct instead of APPARENTLY correct.
So why does the idle needle position dramatically effect the full throttle performance?
A friend (and fellow engine 'nut') and I believe we may have the answer. We think it has to do with venturi effect and fuel atomization.
If you look down the throat of the carb (in the full throttle position) you will see that the idle needle is retracted just clear of the end of the spray bar tube. In the three engines we have 'sorted' recently, the gap between the end of the needle and the end of the tube is about .002" to .003" when correctly tuned. Remember that it is poissible to get a good idle and transition with the idle needle much richer than this - i.e. a much larger gap, but this seems to result in poor and unreliable full throttle performance.
We think that this is probably because the venturi effect at the end of the spray bar tube is compromised if the gap is greater than a few thou. This, in turn, results in less fuel 'draw' which, of course, "looks' like a lack of of tank pressure. We believe it also reduces the atomization of the fuel so that the engine 'acts' lean even while it's smoking.
So, forget about drilling out pressure nipples, changing tank positions, sealing carbs etc at least for a while - It's all too hard and, on my engine at least achieved nothing. Try checking that idle needle to spray bar tube end clearance and working from there to see if that solves the problems.
Good luck,
John.
11-06-2005 | 07:10 AM
#9
My Feedback: (21)
RE: GMS Engine problem
Turk1....
....I made sure the exhaust pressure nipple was open before I ran my engine. I also
redrilled the misaligned fuel inlet before I ran my engine. When I did run it, I found
the engine was bogging (lean) coming up from idle on the low end. I had to open
(richen) the low end screw 1/4 turn.
How did the adjustmants work out on your engine ?
FBD.
....I made sure the exhaust pressure nipple was open before I ran my engine. I also
redrilled the misaligned fuel inlet before I ran my engine. When I did run it, I found
the engine was bogging (lean) coming up from idle on the low end. I had to open
(richen) the low end screw 1/4 turn.
How did the adjustmants work out on your engine ?
FBD.
11-06-2005 | 09:14 AM
#10
RE: GMS Engine problem
Dave,that comment/experience was not belongs to me.I only saw and forward it to this thread.And I think the main theme is, to keep low end needle as close as possible to spraybar.Did you try such a combine adjustment as JDW describing above??
11-06-2005 | 03:33 PM
#11
My Feedback: (21)
RE: GMS Engine problem
No....I just checked mine, the main needle is 2 and 1/4 turns out. There must have
been something way out of whack for JDW's engine to need 6 turns plus to get the
high speed set. I would guess that it was either lack of fuel pressure, or a restricted
fuel line, or some garbage in the main needle.
Dave.
been something way out of whack for JDW's engine to need 6 turns plus to get the
high speed set. I would guess that it was either lack of fuel pressure, or a restricted
fuel line, or some garbage in the main needle.
Dave.
11-07-2005 | 05:14 PM
#12
Senior Member
RE: GMS Engine problem
ORIGINAL: Flyboy Dave
No....I just checked mine, the main needle is 2 and 1/4 turns out. There must have
been something way out of whack for JDW's engine to need 6 turns plus to get the
high speed set. I would guess that it was either lack of fuel pressure, or a restricted
fuel line, or some garbage in the main needle.
Dave.
No....I just checked mine, the main needle is 2 and 1/4 turns out. There must have
been something way out of whack for JDW's engine to need 6 turns plus to get the
high speed set. I would guess that it was either lack of fuel pressure, or a restricted
fuel line, or some garbage in the main needle.
Dave.
No.....
That's the very point of JDW's post - there was nothing out of whack other than the low speed needle setting.
His engine could be changed from a bad behaving poor fuel drawing engine that needed 6 turns plus on its main needle to run OK on a vertical line to a really good performing consistent engine that needed 3 odd turns of main needle at will, just by adjusting the low speed needle. I'd have not believed it had I not been standing next to the thing when he was doing it!
11-07-2005 | 05:18 PM
#13
Senior Member
RE: GMS Engine problem
ORIGINAL: Turk1
Dave,that comment/experience was not belongs to me.I only saw and forward it to this thread.And I think the main theme is, to keep low end needle as close as possible to spraybar.Did you try such a combine adjustment as JDW describing above??
Dave,that comment/experience was not belongs to me.I only saw and forward it to this thread.And I think the main theme is, to keep low end needle as close as possible to spraybar.Did you try such a combine adjustment as JDW describing above??
The needle/spraybar gap mentioned makes an enormous difference to how the engine behaves at full throttle.
