Squid

Hi Wayne,

Opps I forgot to mention, I have been running an exhaust deflector all along, maybe thats why It doesnt seem to need an additional baffle in the exhaust.

Your tuning method seems pretty spot on. I use a non scientific method, combining a pinch test and acceleration test, just peak on the main needle, then do the following:
1) High speed run 10 secs
2) Idle 10 secs
3) Pinch fuel inlet pipe as near to the carb inlet as possible (should run 2-3 secs, picking up slightly). No need to wait till motor cuts. If picks up (and possibly dies) immediately, too lean. If takes 5 secs to pick up, too rich. Adjust idle screw 1/8th turn accordingly and repeat 1-3 until happy.
4) Repeat 1 & 2
5) Test transtion from idle to full power with a smart shove forward on the stick. Should accelerate cleanly. If not, probably a tab rich. Lean idle screw 1/8th turn are repeat whole procedure from 1.
6) If ok, re-peak the main needle if necessary and check the vertical. If too lean on the vertical richen a click the main a click or two.

Hope that helps!

Regards,
Mark

Wayne Miller

Hi Squid,

I your method is what I would normally do, however I did find a hard time getting an initial starting point with the GMS carb. Hence, the peaking of both the high speed and low speed needle at full throttle first, as described earlier. This is a good "ball park" setting and is pretty close, fine tunig the way you suggested should put it "spot on".

I suspect the exhaust deflector would help with the muffler pressure.

Thanks for all your help, I'm sure all GMS .47 owners appreciate your work.

It would be good if we can get some more feed back.

Great working with you!

Fly4Fun,

Wayne

Squid

Wayne its been a pleasure!

It is great indeed how the internet can bring together modellers from all over the world to help solve problems and reach a common goal.

I look forward to hearing how others are getting on with their GMSs and how much the other capacities of motor are affected apart from the 47s.

Cheers
Mark

AirGar

My Feedback: (7)

Hey Wayne,

Have not forgot about you, or this thread. If it ever dries out where we fly, my Sonic/GMS 47 will be the first thing I tackle.

What I want to do first, is compare (visually) the one that runs like a clock, to the one that quits at full throttle. Stay tuned (pun intended)

Gary

Turbobeaver

Hi all.Reading this posting on the GMS .47 has been most interesting and informative.It's kind of like reading a good murder/mystery novel.You can't wait to get to the end to find out "who done it"!

After reading all of the above information,I was thinking much along the same lines as some of the other posters as to areas that I would address.It seems most have been implemented but I did happen to think of one other.The older style "tuned muffler" consists of 3 separate components.The front housing,center aluminum pipe section and rear exhaust outlet section.With two major joints on this style of muffler,you may be loosing a lot of your back pressure through these joint area's.Has anyone RTV'd these joints up and tested the engine to find out if it makes any difference in performance or not?This problem maybe contributed to one thing or a combination of things but for what it's worth,I thought it was worth mentioning anyways.Good flying gents!

Flyer Freq

As time wears on, the joints in the muffler leak more and more and are usually distinguishable by black, oily soot oozing from them. This has not caused my .47 any running problems.

Wayne Miller

Hi Gary and Turbobeaver,

Gary,
Hope your field dries out shortly, we look forward to your input!

Turbobeaver,
The joints on my "silver" style muffler were very tight, infact it showed no signs of the black liquid seapage that usually occurs at bad muffler/engine joints, but it would be a good idea for others to check. I look forward to the day I can get to see the air museum in Ottawa - last time I was there I did some white water rafting. Glad your enjoying the post, I'm really enjoyed working with this group of modelers, they are great and its been very productive.

Fly4Fun,

Wayne

Hurricanebill

My Feedback: (10)

Hi,
Just thought I would chime in and let everyone know I am selling a new in the box GMS2000 0.76
I will sell for $75. paid $90+tax at my lhs I bought it for my 1/7 AT-6 Texan but never finished it ,
pm me or email me @ [email protected] I will send pics if requested
see GMS.com for stats on the 2000 0.76
comes with muffler& gasket and allen tools and i will throw in an new in pack OS glow-plug and a new carb cover for storage
thanks all.[8D]
Bill Ellis

Wayne Miller

Hi Bill,

Thanks for the information, this forum is for the resolving of a GMS problem, and the wrong place for your ad. You probably would get a better response if you post in the "MARKETPLACE" section.

Good luck on selling your engine.

Fly4Fun,

Wayne

Flyer Freq

O.K. Guy's!

We had our annual Frozen Finger Funfly today, and my friend finally turned his .47 over to me. The first thing I noticed was that his carburator has two O-rings sealing it, where it mounts to the crankcase, and my old .47, which runs perfectly, has only one. I would say that he should have a better seal around the base of the carb than mine does, but the O-ring is really stiff and hard. I can't help feel that changing to a silicone O-ring would help here. I will try to get another O-ring, as I am afraid I knicked the O-ring while removing it.

I next removed the inlet nipple. About 1/3rd of the hole in the brass insert was covered by the edge of the carb body. When I compared it to mine, the edge of the hole in the brass insert was lined up with the edge of the hole in the carb body. The newer carb appears to be consistant with the findings you have made with the bad runners. I took the rest of the parts off the boddy and laid the carb on its side and knocked the insert out with a rubber hammer. It came out with a couple firm taps. The hole in the insert was uniformly round on one side of the barrel, but the other side resembled the shape of a kidney. I can't be sure which side was facing the nipple. When I compared the holes in the brass insert from my good carb, the holes in mine were nice and uniform on both sides.

Everything else between the two carbs looked identical. At this point, I reassembled the newer carb, being careful to line up the holes. I used a nipple from an air tool to slide over the end of the brass insert. I then pounded the insert into place. I made sure I didn't pound it in too far. I wasn't sure if installing the high speed needle barrel would pull the holes out of alignment when tightened down, but it did not. The barrel is tight and everything is in proper alignment. All that remains now is to run the engine with a new base O-ring. I wish I didn't have to change the O-ring, as now I won't know if the engine runs well, if it was the alignment of the holes, the new O-ring or both.

I will see how quickly I can get a new O-ring, and report back. Engines don't run particularly well in the severe cold we get here, but I should be able to tell something. I may try putting the newer carb on my engine to see how it does. After all, my .47 doesn't have that O-ring inside the crankcase.

Till later!!!

Andy

Wayne Miller

Hi Andy,

Thanks for the very detailed report.

I was wondering if the brass insert would come out without damaging it, and was afraid to try. I'm assuming you drove it out from the inside of the carb - if so, did you use a brass punch? If not, could you explain how you did it?

I also fly in cold weather, we usually put a couple of drops of lighter fluid in the carb immediately before starting, it works well. You may want to give it a try.

I look forward to your next report.

Thanks for taking the time to help us out, its really appreciated.

Fly4Fun,

Wayne Miller

Waco Driver

Leakage from the front bearing seems to be a common complaint on the GMS 47 and Tower 46. Excessive crankcase to crankshaft clearance in the area between the ball bearings certainly affects crankcase base compression and fuel draw ability. Has anyone taken the time to remove the ball bearings and check the actual running clearance between the crank and the crankcase? If the clearance is more than .0015", I would be very suspicious. While air and fuel leakage from the front bearing area may not bother an engine that is not used for aerobatics, it will always show up as a poor ability to draw fuel when the nose is pointed up.

The modifications to increase fuel pressure and remove the flow resriction in the carb have apparently helped the fuel draw ability of the engines involved. I do not feel that they have got to the root of the problem however. It would be interesting to see if these engines can be flown without muffler pressure.

Before the onset of cold weather I was just starting to help a new student learn to fly with a new GMS 47. While it ran good at times, I had it flame out a few times for no apparent reason. I will be looking at it in the near future and my first investigation will be to look at the above mentioned clearance as his engine also drips fuel from the front bearing. I will report my findings in due course.

seagull extra

My Feedback: (12)

I have just read this post as I too have had simular problems with my GMS 47. I had a very frustrating time with mine this summer when I mounted it in my See Bee 40 size pattern plane. I had run the GMS in my trainer before and It seemed okay, but once I installed it on my See Bee I would always lean out in arobatic flight and dead stick. I also had a MDS 40 so I swapped it out with the GMS and it would do the same thing as the GMS so I naturally thought it was somthing with the installation. But I could not find any problems with the fuel system. At our annual KWFD scale rally Flite Craft had a great deal on Super Tigre engines so I bought a G-51 and put it in the SeeBee and it has performed great right from the start.
I did check under the inlet nipple on my carb and the hole does not line up on mine, but by blowing air through it I would say it doesn't seem to be affecting flow much but I will rill it out anyway, just incase I need to use this motor in the future.
PS. I ended up putting the MDS 40 with the GMS old style muffler on my trainer with floats
and it has crazy power! This plane is at my cottage and I did not have my tack but it absolutly screamed with that pipe.

Wayne Miller

Hi Waco Driver,

I have attached a long piece of fuel tube to my carb input nipple, then blocked both the exhaust port and carb throat and blown into the fuel tubing to check for front bearing leaks. There was a little air escaping, but very little. Since I have both an older and newer GMS .47 (the newer one runs great) I compared the two and both leaked air about the same.

Since sealing the carb and enlarging the carb input and exhaust nipple, my "bad" engine runs fine now without the extra exhaust baffles.

I noticed we live fairly close together, and since we have 3 GMS's between us, perhaps we could do some comparisons. Send me a PM if your interested in getting together.

Thanks for your input, I look forward to your findings.

Fly4Fun,

Wayne Miller

Flyer Freq

Hey Wayne!

I actually drove the insert out of two carbs. The first time, I heated up the carb body, and used a rubber mallet to hit the threaded end. The threads were not damaged at all. The body of my carb is worn out in the area of the jam bolt, so I wasn't worried about damaging the body. I didn't heat the body, I just hit it with the mallet a couple times. It came out with no damage. No punch is needed.

One possible fix for the alignment issue, would be to put a fiber washer on the inside of the carb, around the seat of the brass insert, as well as the one on the outside. It would move the brass insert out just enough, and it wouldn't allow the over tightening of the needle valve barrel to pull the brass insert in too far.

It is possible that www.smallparts.com may have these washers, I have not looked yet.

By the way, I use the lighter fluid too, works great!

Waco Driver:

I have heard the leaky bearing theory before. I wish I could quote some sources, but I'm afraid I don't remember the exact details or where I read this information[sm=surprised.gif]. It may have even been on RCU. Oil leaking through the front bearing offers lubrication. The way the two stroke engine is ported, some leakage is necessary for proper fuel flow. I heard of someone with, either a GMS .25 or .32 who didn't want the fuel leaking from the front, so they replaced it with a sealed bearing. The engine no longer had the power or RPM it once had. Surprisingly, Mecoa replaced the engine, in spite of the modification. I am counting on my memory here, and I am missing the details, but the leak is not as much of a factor as it may seem. I will say, that the fuel leaking from the front of mine is hardly noticeable. I remember seeing it when I had it on the break-in stand, but not since being in the nose of my SE. As I have mentioned before, my engine is on its 5th year and is still going strong.

Andy

Wayne Miller

Hi Andy,

Thanks for the tip on getting the brass insert out - do you think that perhaps a "C" clamp may work as a "press" to remove the insert?

Just a thought, whenever I'm stuck for small fiber or rubber washers, I use "hole" punches to make them. I punch the small hole first, then punch around it with a little larger punch. This gives you a washer.

I have some gasket material, but have also used winshield washer bottles, margerine tub lids, inner tubes, leather, the inside of fuel container lids etc. when I felt they would work for a certain application. Such as: spacers, fuel filter gaskets, washers, seals etc.

You can usually buy these punches at places where they sell tools.

If your stuck for washers, you may want to try the above.

In your case, the washer would have to be fuel and heat proof.

Thanks for getting back to me.

Fly4Fun,

Wayne

Wayne Miller

Hi Seagull Extra,

Glad to hear from you! I was at the KWFD as well.

If the engine was working OK on one plane, but not this one, then I would suspect a fuel delivery problem. Either tank location, fuel restriction, or air in the fuel.

If all these are OK then you may want to try the things discussed above, such as adding extra pressure to the fuel tank by drilling out the exhaust pressure nipple to the next size, or by adding an exhaust extension to create a little added pressure to the tank.

Hopefully, all the people working on this problem will get to meet someday. I hope GMS appreciates our efforts!

Keep us up to date on your progress with the engine.

Fly4Fun,

Wayne Miller

seagull extra

My Feedback: (12)

Hi Wayne
One other thing I forgot to mention was that I also tried a OS muffler on the Sea Bee with the GMS motor and it would still dead stick when subjected to arobatic flight. I also lost about 1000RPM with the OS pipe but I too thought muffler preasure was a possible cause for the flame outs. One good thing is I now have a lot of practice with dead stick landings and somehow I managed not to lose the plane. I sure hope my GMS .76 that I am putting in my Seagull extra 300 does not have these problems.
By the way I don't live too far away from you. I am in Elmira.

Wayne Miller

Hi Seagull Extra,

I also have a GMS .76 and fly it on 15% nitro with a Fox RC idlebar plug and it works great!

I'm sending you a PM. Please check your INBOX.

Fly4Fun,

Wayne

Flyboy Dave

My Feedback: (21)

I'm going to break out and mount up a GMS .47 tomorrow. I will
be checking out the fuel inlet thing, and see if I can help out. I like
the engine....

Dave.

Flyboy Dave

My Feedback: (21)

Well, it looks like there certainly is an alignment problem in the fuel
inlet spigot. I put a short piece of fuel line on the carb and blew into
it with the barrel wide open. Even at 3 full turns out on the high speed
screw....it seemed like it was restricted, and hard to blow air through.

This picture wasn't easy to get, but you can see the partial restriction.
It's not really as bad as it looks, due to the angle I had to use to get
light into that small hole....the restriction is more like 40% (eyeball)
it looks more like 50% in this pic.

Dave.

Wayne Miller

Hi Flyboy Dave,

Thanks for the picture, I know it must have been hard to get, it cleared a lot of things up for me. My brass insert was rotated and was off center. Freq Flyer stated he was able to fix his by aligning it in and out, and I didn't really understand, now I know why.

So it appears it can be out of alignment either in/out or rotated.

I think the restriction is also worse when the brass inlet nipple is installed, I think the base of the nipple also covers part of the hole when it is fully seated.

Keep us informed of your progress.

Fly4Fun,

Wayne

Edited for typo

Flyer Freq

Wayne:

The c-clamp would probably work fine, to press out the insert, as long as the carb/insert is placed between a couple pieces of wood, or something to protect the soft metals. I like your washer making idea. I really think that putting a washer on the inside, is the only way that the insert will stay in the right alignment, as vibration will likely cause things to shift.

Flyboy Dave's picture is a good duplicate of the carb I am working with, which leads me to believe that the specs are off at the factory. Has anyone made MECOA aware of this site, they should probably be made aware of all this information.

Andy

Wayne Miller

Hi Flyer Freq,

It would seem that if the hole is rotated slightly, you could drill it out with no problems, however, if the hole is too far "in" or "out" then moving the hole back or forth would be the best option. The reason for this would be that when the hole is just rotated, the end of the brass insert would be in the center of the carb opening. When the brass insert is too far in or out, then the end of the insert would have to be repositioned to the middle of the carb opening.

I'm not sure if MECOA or GMS is following this thread, nor do I know how to get in touch with them, but they certainly should know - we are putting a lot of work into solving this common problem.

Again, thanks for your input.

Fly4Fun,

Wayne MIller

Flyboy Dave

My Feedback: (21)

I gave the brass insert a couple whacks with a wood block protecting
but it wouldn't budge. My brass insert wasn't twisted as well as out of
alignment, so I decided just to drill it. I used a # 44 drill, which is .085
or 2.2 mm....anything close to that will work. The drill did drift slightly
into the aluminum as I drilled the brass, and I did hit the threads a bit.

I figured this would happen, but it's OK....and I lock-tited the nipple back
in, and I don't anticipate any problem. I forgot to look at the inside of
the fuel nipple itself for any restrictions or problems. However, I gave it
the "blow test" with the fuel line....again with the barrel all the way open,
and manipulating the needle from fully closed to fully open (about 5-6 turns)
the flow seemed to be much improved, and linear.

The good, the bad, and the ugly:

1. Double o-rings on the needle...good
2. See the scroring in the barrel ? (not the throttle sleeve)....bad
3. In the fully closed position, the barrel guide slot is exposed....bad
(this could be one of those "engine won't shut off problems" ? )
4. See how the mounting flange on the carb is "knarled" ? ....bad
I wonder if the carb pinch bolt was out of alighnment os something ?
I don't recall if the carb was off the engine when I originally got it.