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

Wayne Miller 10-28-2004 04:10 PM

RE: GMS Engine Tuning Problem
 
Hi,

I agree that in theory the baffles should not be needed, however I just got back from the flying field and have tried several things. The results are below.

First I'll re-state that this on the older style GMS, and all air leaks have been sealed, except for a very small amount of air escaping through the front bearing. Some state this is normal - I'm not sure. I should also let you know my newer GMS works great and so I have experince with both styles.

Today I tested without the baffles, and also with different number of baffles. In all cases I ran with a 12.25 X 3.75 prop.

I should let you know the older GMS works fine with the newer GMS muffler. So I have concluded the problem is with the muffler and the pressure feed. If you have any other suggestions to increase the pressure feed, I would appreciate them.

I reinstalled the older muffler and worked with it.

I first tested with the two baffles as shown in the previous picture, and all worked fine, adjustments were easy, idle was good and high speed was constant.

Second I tried smaller baffles, that is, 1 inch instead of 1.25 inch. This gave me a broader adjustment range at high speed, but I did get more RPM. The engine would quit after a while at full throttle for no particular reason.

Third I removed the baffles completely and again I got more RPM but the engine would quit running at full throttle after a while.

Fourth, I installed just the original first baffle (1.25 inch) at the front of the muffler. The muffler was a little louder, but all adjustments were easy to make. The difference in RPM was 200-400 less than without any baffles installed in the muffler.

I settled on just using one baffle, the one closest to the front of the muffler and flew the GMS with a Somethin' Extra for 6 flights with no problems.

I'm convinced the problem is with either the fuel draw, or low exhaust pressure to the tank. Whatever the reason, the baffle does the trick for me.

In this case I have a working, flying engine instead of sticking it on the shelf.

I appreciate everyone's input, however, if you haven't tried the above, and are commenting, I should let you know I would have agreed with everyone BEFORE I got this engine. If you have an old GMS .47 that isn't working, give it a try, I think you'll be surprised at the improvement. In one of the previous posts someone stated "you gotta do what you gotta do to make it right" - good advice.

If you have any other suggestions I can try, I will give them a shot, just let me know.

If you have one of the older GMS .47 with the same problems, I hope you will give the above a try and give us your feedback.

Thanks for your help,

Fly4Fun,

Wayne

AirGar 10-28-2004 06:39 PM

RE: GMS Engine Tuning Problem
 
Wayne,

The 2 47's I have are the newer ones, both with the "tuned muffler". What gets me is, one has been flawless outta da box... :D , while the other is cutting out at full throttle. I haven't tried anything yet, but I will let you know what I find out with mine.

Both running the same fuel, same plugs, same prop (APC 9x8) and both mounted upright. Doesn't make much sense does it? ;)

Glad you got yours running. If it came down to it, and I couldn't get it to run right....I'd probably take them both apart and check/compare everything before I installed a baffle. Ya just never know....I may end up doing what you did! lol

I DO know they will run as they come from the factory, so I'm sure my stubbernness won't allow me to go your route unless it's a last resort.

BTW, did you try relocating the pressure nipple and/or enlarging it? Perhaps there a burr/flashing in it or the muffler causing restriction? I'm sure you checked this, but thought I'd ask anyway. Maybe that's what I shoud do first....compare mufflers.

Gary

Razor-RCU 10-28-2004 06:52 PM

RE: GMS Engine Tuning Problem
 
I need to get a GMS and the Sonic so I can play on the cracked dirt with Dave and gary----

I would like to argue with someone but A. I don't have this engine 2. I am not smart enough to know my own point of view and c. Why would any group decide on GMS for club racing? :)

AirGar 10-28-2004 07:00 PM

RE: GMS Engine Tuning Problem
 

ORIGINAL: Razor-RCU

I need to get a GMS and the Sonic so I can play on the cracked dirt with Dave and gary----

I would like to argue with someone but A. I don't have this engine 2. I am not smart enough to know my own point of view and c. Why would any group decide on GMS for club racing? :)
James,

We agreed on that combo, as not everyone has the moola like you and I. :D

I have another (yes, #3 NIB) that I'd be more than willing to part with.....didn't you say you had an extra Rossi 45, or Jett 50 lying around gathering dust? ;) :D

Gary

Wayne Miller 10-28-2004 08:08 PM

RE: GMS Engine Tuning Problem
 
Hi AirGar,

I feel bad that you have the same problem, but I'm glad I got someone to troubleshoot with.

I did check the exhaust pressure nipple, and it is clear - however, I'm not sure if making it a little larger will help. I'm reluctant to make "destructive" fixes (drilling) except as a last resort, I don't like to order new parts, so I always try "fixes" that can be easily undone. You suggested relocating the pressure nipple - any suggestions where it should go?

I do know the local SuperTiger fans always drill the fuel nipple (into the carb) one size larger and this fixes their fuel delivery problems.

If you suspect the problem is the muffler pressure, see if the fuel in the line (residue from filling) migrates towards the tank when the engine first starts. Note, at first starting the tank begins to pressurize, after it starts, the tank is pressurized and the fuel moves slowly, so you have to see if pressurizes it when the engine first starts.

If lack of pressure seems to be the problem, I would first try the "good" engine muffler on the "bad" engine, if the problem clears up, then we know it is the muffler - if not, then it is something else. If the problem is in the mufflers, then very carefully dissassemble the second muffler and examine the exhaust nipple, both ends, before removal and see if there is any differences. Look at the openings of the nipple to see if there is any metal flashing or if there is special orientation compared to the other. This is the only thing I can think of that may be different between two similar mufflers.

The other thing you may want to try is to remove the carb from the "good" motor to the "bad" motor, if the problem is fixed, then the carb settings will be the problem. If the problem is not fixed, then it is an air leak, fuel delivery problem, muffler.

My motor is working fine now, but I'm sure there is a better fix than the baffle, I'll post anything new I find, please let me know what you find.

Thanks for your help.

Fly4Fun,

Wayne

Wayne Miller 10-29-2004 06:37 PM

RE: GMS Engine Tuning Problem
 
Hi AirGar,

Just an update.

I was flying today and all went well with the baffle in place.

However, I put a lot of thought into the problem and when I got home, I decided to dissassemble and take a look at the differences between my "old" and "new" GMS engines fuel delivery systems.

One of the things that did not look right was the fuel opening into the carb under the fuel nipple (the one the fuel line attaches to). It did not seem to quite line up with the hole from the fuel nipple.

To explain, if you take the fuel nipple off of the carb body, you can see a brass insert under it in the carb. The brass insert has a hole in it. The hole in brass insert did not quite line up with the hole in the fuel nipple. It seemed to pass air OK, but I'm not sure about how it delivers fuel. This could be causing the fuel restriction at full throttle - I'm not sure yet, I still have to test. But this would explain why more muffler pressure helps at full throttle.

I then reassemble, attach a fuel tube to the carb nipple, and blew with the throttle wide open, and needle valve backed out a little. I listen to the amount of escaping air.

I then removed the nipple again and carefully hand drilled (not electric - I didn't want to damage the threads for the nipple) through the brass so the hole to the carb was slightly larger. I inserted a pipe cleaner into the needle valve opening to catch the brass particles.

I expected that if this slight restriction, due to misaligned holes, was causing the problem, this would allow the fuel to flow freely into the carb from the nipple, since the openings now line up.

I also drilled out the fuel nipple and exhaust nipple to the next size larger - I figured this wouldn't hurt anything, and may help. Now when when I reassembled, put the needle valve back to the last setting, and did the "blow" test at full throttle, more air escaped with less resistance.

I don't think I'm going to be flying this week end, but if I do, I'll let you know what the results are. I expect the engine to perform better, and I may be able to remove the baffle.

If possible, would you mind carefully removing the fuel nipple from your "bad" engine and see if the hole in the brass insert in the carburettor lines up with the fuel nipple?

Hopefully we are getting closer to solving the problem, I let you know my testing results as soon as I know.

Thanks for your help.

Fly4Fun,

Wayne

AirGar 10-29-2004 10:28 PM

RE: GMS Engine Tuning Problem
 
Ahhhhh Wayne....I think your onto something Buddy!

I'll be gone all day tomorrow, so I'll try to take a look at that on Sunday.

Maybe you should try the first flight without the baffle.....

Look forward to hearing your result!

Gary

Flyboy Dave 10-30-2004 12:24 AM

RE: GMS Engine Tuning Problem
 
You know....I went in and looked at my engine....I backed the main out
about 3 turns, and blew into the carb/fuel inlet line....

....it seemed like it was pretty restricted. :eek: Not a real scientific test, I
know....I'll have to look further. ;)

FBD. :D

Wayne Miller 10-30-2004 08:29 AM

RE: GMS Engine Tuning Problem
 
Hi,

Thanks for checking, I will be interesting to see what we come up with.

Just a hint. I was really concerned about damaging the threads where the nipple goes in and was very careful when I did the drilling. If I was to do it again, I would first remove the needle valve, then remove the fuel nipple, drill the fuel nipple to the next size larger (be careful to keep the drill in the center of the nipple!), then put the nipple back in and use it as a guide for the same drill to carefully drill through the brass insert. Again, I would put in a pipe cleaner or piece of rag in the needle valve hole to catch the brass filings when drilling.

Its raining here today, and the Yahoo Weather site is forcasting rain for the next few days, so I may not be able to test for a while - if there is a break in the weather, I'll let you know the results as soon as I can.

Fly4Fun,

Wayne

Wayne Miller 10-31-2004 04:52 PM

RE: GMS Engine Tuning Problem
 
Hi,

Just an update.

After I drilled out the carb input, I ran it today in the back yard first with the baffle left in - it worked great except it would tend to lose power with the nose pointed up.

I removed the baffle ran the engine again, had to readjust the high speed settings, but the engine ran very well.

It looks like tomorrow will have a cloudy, rainy day with some sunny periods. If I can, I'll test it at the field tomorrow, only "real" flying will tell us how it works.

I suspect the problem was fuel starvation at high throttle.

Fly4Fun,

Wayne

flyoz 11-01-2004 02:18 AM

RE: GMS Engine Tuning Problem
 
all very interestin stuff guys +
my 2c's worth; I read with the TT motors for example, you should always check the fuel pressure nipple that it doesnt have any mold flash/residue/blocks or isnt completely blocked.
That will cause hassles Maybe your baffle overrode this?

Wayne Miller 11-01-2004 09:01 AM

RE: GMS Engine Tuning Problem
 
Hi Flyoz,

Thanks for your input, we are heavily overcast this morning with a few sunny breaks expected, I'm going out to the flying field and will let you know how the motor works with the exhaust pressure nipple, input nipple and carb input hole drilled out.

I'm hoping all will go well.

Fly4Fun,

Wayne

Wayne Miller 11-01-2004 07:35 PM

RE: GMS Engine Tuning Problem
 
Hi,

It was very cloudy with a few sunny breaks today and I had 5 flights with the GMS .47 today without the home made baffle(s).

The first flights two were used to fine tune and adjust the engine (with plenty of landings to tweek the needles) and the last 3 flights were great without adjusting the carb.

I'll go over what needs to be done. The problem seemed to be the fuel hole that is below the fuel input nipple in the carb, not lining up with the fuel nipple hole. I think this causes fuel starvation at full throttle.

What I did was to first carefully drill out the exhaust nipple and carb input nipples to the next size larger (to 5/64 of an inch). I then "free handed" carefully drilled the brass insert below the carb nipple to 5/64 inch (in the future I would drill the nipple, then install it, use it as a drill guide to carefully drill into the brass insert to avoid any damage to the carb's nipple threads). The new, larger holes now lined up and gave me better fuel draw and better "exhaust to tank" pressure. Be sure to remove any brass filings when you drill the carb. Note: Drilling the holes will modify the engine and therefore void your warrantee, so if you chose to do this, be very careful since its at your own risk.

At first I had a difficult time adjusting the engine high speed and low speed settings - these seemed to intereact with one another. Example, leaning the idle, also leaned the top end - I would readjust the top end, and it would affect the low end, and I ended up with a never ending cycle.

What worked for me was to:

1. First go to wide open throttle (WOT), adjust the high speed needle for max RPM then, while while still at WOT, tweek the low speed adjustment to fine tune the engine at WOT.

2. Then go back and adjust the high speed needle and then back again to tweek the low speed adjustment. Keep this up until you have the best WOT performance.

3. This will be very close to the proper adjustment at both WOT and idle.

4. After you get the best WOT with both high and low speed needles, carefully idle down and adjust your low speed RPM (by programming the transmitter or adjusting linkage).

5. Once you find the best idle speed for your prop, then "poke" full throttle. Turn the low speed adjustment no more that 1/4 turn either way until the acceleration from low speed to high speed is smooth. My low speed needle adjustment needed to 1/8 turn leaner (tightened "in" ) .

6. Test at WOT with plane level and nose up. Mine worked OK at this point.

The final adjustments for me were:
Turn in high speed needle in until it just stops, then back out 2 1/2 turns.
Turn the low speed needle in until it just stops, then back out 1 3/4 turns.
This may not be dead on for you, but will give you a good starting point.

I hope the above will help someone else make their GMS .47 the power house and reliable engine that it can be.

I hope someone else will give the above a try and let us know if it worked for them - this one test is not enough to verify if this is the "fix".

If you have any questions, or I can assist with anything, please let me know.

Fly4Fun,

Wayne Miller

flyoz 11-02-2004 12:05 AM

RE: GMS Engine Tuning Problem
 
Outstanding Wayne- boy you sure earn your wings for dedication.

Im glad the "check the holes for blockages" idea was it :) ( n0w I can tell my wife I can prove Im a legend lololol)

Well done mate and happy flyin.
PS the whole string has been a real learning experience again well done mate and 10 points for effort :D

Wayne Miller 11-02-2004 08:17 AM

RE: GMS Engine Tuning Problem
 
Hi FlyOz,

Thanks, however, we still have to get some other people's tests and results in before we are sure this is it.

Nice country you live in, I've only worked in Sydney and Melbourne and liked the people and really enjoyed the zoo and aquarioum in Sysney.

Fly4Fun,

Wayne

Flyer Freq 11-08-2004 12:29 PM

RE: GMS Engine Tuning Problem
 
Once we know for sure if the alignment of the inlet hole is the problem, replacing the carb body may be the easy solution. It is hard to imagine making the modifications when the body is only $8.99. Here is the link to the carb body with the needle valve in front. Tower also has the carb body for the rear mounted needle valve for $1.00 more.
http://www2.towerhobbies.com/cgi-bin...?&I=LXEGM2&P=7

Andy

Wayne Miller 11-08-2004 05:57 PM

RE: GMS Engine Tuning Problem
 
Hi Andy,

Thanks for the information. If I had known the costs, I would have started drilling sooner instead of being so cautious. The exhaust pressure nipple and the carb fuel nipple would still have to be drilled.

I wonder if anyone else has given the modification a try - it would be good to know if this is a good permenant fix, or if I was just lucky.

Has anyone out there tried it yet?

Fly4Fun,

Wayne

Flyboy Dave 11-08-2004 06:27 PM

RE: GMS Engine Tuning Problem
 
Wayne,

....I'm gonna have a look at mine, but I haven't run it yet, so it will be
just an eye-ball at the passageways.

AirGar said his was acting up....so maybe we can get a first-hand from
him. Our field is under water right now, so it may be a few weeks before
we can see some flying action. [:o]

FBD. :D

Flyer Freq 11-09-2004 01:35 PM

RE: GMS Engine Tuning Problem
 
Wayne:

Just curious, if the problem with the engine going lean at high throttle is due to the inlet hole being offset, why do you say that the carb fuel nipple and exhaust pressure nipple would still need to be drilled out if the carb body is replaced with one that has the hole centered? Not that I feel it would hurt anything...[sm=confused.gif]

Andy

Wayne Miller 11-09-2004 02:16 PM

RE: GMS Engine Tuning Problem
 
Hi Andy,

Your probably right, drilling the nipples may not have been necessary.

I had actually done all three things at once, that is, drill the 2 nipples and the inlet hole at the same time, I had a free day that I wasn't flying, and probably did more than I should. I'm really not sure if all three procedures are necessary or if one would have done the trick. It would be interesting to know.

If you had the time, you may want to try one at a time and really isolate the problem.

Also, I was thinking (I know, its dangerous) if the problem was the carb inlet hole and the inlet nipple hole not lining up, and thus restricking the fuel intake when the nipple was tightened down (by partially blocking the hole). Then perhaps just putting an extra spacer under the nipple flange might hold the bottom of the nipple far enough away from the inlet hole to stop it from partially blocking the inlet hole - this may do the trick and allow the fuel to flow freely.

Its just a thought, its too late for me to try since I've already drilled the hole.

Let me know how you make out with yours, I'm really curious.

Thanks for your help.

Fly4Fun,

Wayne

Flyer Freq 11-10-2004 09:00 AM

RE: GMS Engine Tuning Problem
 
Hi Wayne!

About 4 1/2 years ago, I bought my first GMS Engine. I broke it in on an 11X5 APC and have since been running it with an 11X3 APC on a Something Extra. She had been turning that prop in the 15,500 RPM range, and continuing to get better. This year she broke the 16,200 RPM mark. Pretty impressive! It has hundreds of flights on it, and is still blowing the doors off of all the O.S. .46 FX's at the field. The AX, well, it is still too early to tell. But for the price, it is the biggest bang for the buck. As you can imagine, I have been trying to get people to jump on the GMS bandwagon for a long time. Every time I think I have someone sold on the GMS, they come out to the field with a new O.S.. Well, in brief, a friend finally got a GMS .47, and it does just what you guy's are talking about, dies at full throttle. I have taken a little ribbing over it, thus my interest in this thread. The guy has shelved the engine, and I am trying to get him to look at it to see if it has the offset hole. So,... I don't know if I am going to get the opportunity to play with it to help solve this mystery. I really want a crack at it!

For the record, I have the GMS .76 also, and it too is a beautiful engine. I bought a second one for a friend and ditto on that one. The power compares to many .91's and the idle is incredibly smooth and low. I have been running a 14X6 Zinger on it, on a Dragon Lady. It pulls that big plane through the biggest, prettiest loops you ever saw,... with authority. I am in the process of moving it to another plane, or I would tach it for you.

In short, I believe GMS is the biggest bang for the buck, and am anxious for this problem to be solved at the manufacturing level. Has anyone contacted MECOA about it?

Andy

Wayne Miller 11-10-2004 10:55 AM

RE: GMS Engine Tuning Problem
 
Hi Andy,

Thanks for the information, I also have the .76 as well as the two different models of the .47. I only had the problem with my older .47 with the "silver" muffler without fins.

I hope you are able to try the modification on your friend's GMS. The intent of this thread is to find the source of the problerm so all can make this engine run reliable.

I agree, when a GMS it is running right, I think it is the best bang for the buck.

Please keep us updated on any progress with your friend's engine and hopefully, collectively, we will all get to the bottom of the problem and solve it.

Thanks for your comments.

Fly4Fun,

Wayne

XJet 11-10-2004 02:19 PM

RE: GMS Engine Tuning Problem
 
After much consideration, I just ordered another TT 46.

The GMS engines may have more power (when they're running right) but I've seen others struggle to keep their GMS engines on song and some days they end up spending most of the day in the pits or walking back from the flight line after dead-sticks or engine flame-outs on take-off.

Meanwhile, I just keep on flying with my TT engines, hardly ever touching the needle and with a totally consistent level of power and performance.

For the record, I *do* have a GMS 32 but haven't put it in anything yet.

Wayne Miller 11-10-2004 03:35 PM

RE: GMS Engine Tuning Problem
 
Hi XJet,

We really need someone to give the modification and tuning procedure (described in post number 38) a try. If you know of people at your field, who are having problems, do you think they would mind helping us out and give the modification a try and then get back to us with their results?

Just because it worked for me, doesn't mean it is a valid fix. It may just be a "one time" fix. We need more tests by other modelers.

Any help would be greatly appreciated.

Thanks,

Wayne

XJet 11-10-2004 07:28 PM

RE: GMS Engine Tuning Problem
 
I'll see what they say -- at this point I think they'd try anything :-)


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