Hi Andy,

Thanks for the update.

My city is about as far north as Madison. If you look on a map, I'm almost directly to the east of Madison (although a long ways), past Detroit about 130 miles - 60 miles before Toronto and about 60 miles north of Niagra Falls. I checked the distance, its 1070 Km or about 600 miles, from you. This is about a 10 hour drive plus stops.

I think the Canadian border you are looking at is directly North of you. I've worked all over the world, but the only time I worked in WI was in a small town called Beaver Dam, I flew in for that job.

Let me know how you make out with the carb modification.

Fly4Fun,

Wayne Miller

Save your money on those carb bodies[&o]. I just ran the engine with the "problem" carb with my spray bar. It ran exactly the same as before. I then put my low speed needle in the carb and ran it again. Same problem. Then I put my high speed needle in the carb. Same problem. I then put several o-rings on my Perry carb and installed it. The engine ran exactly the same. It could have been leeking around the multiple o-rings, but the engine sounded too much the same. I put the original carb back on and started the engine again. I took penetrating oil and shot it at the backplate when it started to ping. Things happened real quick, but the engine smoothed out and then died. I tried to repeat this, but I was lucky to hit the backplate the the first time, due to all the prop wash.

The spray bar may have had some to do with the lean high, but it definately wasn't all the problem. The backplate gasket may be it[X(]. It is an o-ring also[X(]. I may try adding permatex to test this theory. Sorry for the wild goose chase[:@]! I really thought I had it solved.[]

Andy

P.S. Sorry for all the emoticons, just trying to make lite of a dissapointing situation.

Now I'm really confused. I talked to the owner of the engine I am "playing" with at our club meeting last night, and one other guy that has an O.S. .46 AX that is the same age as this GMS. The owner of the GMS couldn't believe that I was able to fly the engine at all, based on his experiences with it, before I worked on it, and the AX owner said he was dissappointed too, since his AX would not transition well in the cold, and a vertical transition is out of the question. Do we have the problem figured out or not? Are these two engines just not broken in all the way? Are they designed in such a way that they won't hover well in cold temperatures? I have no answers, and don't know if I can come up with one until the weather warms up considerably. I do want to permatex the backplate on the GMS and see if it transitions better. I at least have to try that.

Andy

Hi Andy,

First I should let you know that I fly with 15 percent nitro and always have some castrol in the fuel - what nitro are you running? If its lower, you may have to play with the head gaskets, however, I have never done this.

Whenever we have an exceptional cold day, and the engine is running too cold to be reliable, you can keep the engine running warmer by putting a strip of aluminum cooking foil around the bottom 1/3 or 1/2 (sometimes more) fins of the motor. Hold in place with a twist tie.

I understand that your mid throttle problem first appeared when you tried to hover. Since fuel draw is more difficult in the nose up attitude, we still may have a fuel draw or pressure problem.

I can not remember, and can not seem to find it in this thread, so I need to ask, did you ever drill the intake fuel nipple and exhaust pressure nipple, if so, to what size?

I drilled mine out one drill size larger, then the engine started to work. I may drill the nipples out two drill sizes larger and give it a try, it won't hurt and may be best for a standard fix. The brass insert on mine has already been drilled so the opening is directly below the fuel intake nipple with the insert fully seated, so this does not need to be done.

Again, your doing a lot of work trying to solve this problem. Thanks for your help and keeping everyone up to date.

Fly4Fun,

Wayne

Thanks Wayne!

No I haven't drilled anything out. Sounds like a good tip on the aluminum foil. I run 5% nitro, with castor in all my engines. I know higher nitro is usually run in the winter. I pulled two of the head spacers to match what I have in my own GMS. I thought it would help, but not much change was noted. In analyzing this, in regard to vertical performance, if I was level and at or near full speed, and I pulled straight up, she would climb out of site. If I am vertical, and cut my throttle to halt my climb, and then add throttle to maintain altitude, the engine dies, If I then go back to idle, quickly, the engine remains running. I drop my nose then, and give her the gun in level flight and we are back off to the races, tearing through the sky like its tail is on fire. Weird and frustrating!

Andy

Flyer Freq,

I would try a little RTV in the Fuel-Return groove.
Or try a double sealed bearing
I posted an article by Dave Gierke in the "Obvious Air Leak" thread that helped me.

Thanks Spicoli!

I'm afraid I have to plead ignorance, though[sm=confused.gif]. What are you referring to as the fuel return groove? I will read your article on the bearing seal. Thanks!

Andy

Flyer Freq,

Inside the engine there is a channel that goes from the front of the carb to the front bearing.You have to take out the front bearing to see it.

Thanks Spicoli! I realized that after reading the article. Not sure if that will help this engine or not, as I can shut this engine down easily. Did you put the rtv in, in the carb area, or the bearing area. If it was the bearing area, did you heat the casting to get the bearing out?

Andy

I put the RTV in the channel through the front.
The bearing didn't need heat to come out.All the bearings I've messed with before that one did need the case heated.
I didn't do this until I checked for leaks at every other spot possible

I don't know if you were one of those who drilled out the pressure nipple on your muffler or not but those who do this should be aware that doing so can often have a very negative effect.

What is sometimes forgotten is that there's no check-valve in the pressure line so the bigger the hole in the pressure nipple, the quicker the pressure in the tank can bleed OUT once you cut back to a lower throttle setting.

If the hole is to big, this can produce major transition problems.

Here's the scenario ---

You are running at full throttle so the tank build up a steady pressure.

You cut throttle back to a lower setting and the engine continues to run -- but the pressure in the tank now reduces because the tank-pressure is now higher than the muffler pressure so the flow in the pressure line reverses.

You hit the throttle again and suddenly the engine is trying to run at full-throttle RPMs with just a fraction of the pressure it normally has at those throttle settings -- because the tank has yet to repressurize.

I've had quite a bit of success in "taming" badly behaved engines (which won't transition for ****e) by varying the size of the pressure nipple. Sometimes less is more, especially in 3D stuff where you're more interested in sustaining a constant tank pressure during pretty regular and frequent throttle variations.

Thanks XJet! Very interesting stuff! If a person wanted to reduce the nipple size, where do you get other nipples? I know Dubro makes some nipples that are brass. Can you just fill them with solder and redrill, or is there a better way or better source ???

Andy

Hi Andy,

To reduce the hole size, you can fill with solder and redrill, however, I always like to go with temporary modifications to test with first.

Example: You may want to find a piece of brass tube, or fuel filter, with a smaller size hole - or as an alternative, take a 1 in (2.5 cm) piece of brass tubing, fill it with solder, drill and then insert in the exhaust pressure line (to the tank) to do your testing. This will give you the restriction without modifying the nipple. You can make up several of these with different size holes, and take them to the field to test with. If you find a hole size you like, then modify the exhaust nipple.

Just a suggestion, hope it helps.

Fly4Fun,

Wayne Miller

Thanks Wayne!

That is a good idea! I also noticed that the inside diameter of the nipple for several of the GMS engines vary. They are .75 cents each, from Tower, and may not be a bad thing to have in the flight box. Your suggestion, is definately quicker than waiting for an order to come in.

I guess my next course of action is to rtv the back plate, run the engine and see what the results are. If they are not what I am looking for, make some orifices out of brass tubing and play around with varying the sizes. I want to make the orifices very short, however, because the length of the orifice will likely have as much effect as the diameter. I will keep you posted!

Andy

Hi to all, my friend and I have the same problems with the GMS engines. He has the .40 and I have the .47 with remote needle. He has about a gallon thru it and I have about half a gallon thru mine. The engines die at take off, die at full throttle ( in flight) and sometimes die at mid throttle for no apparent reason. High spead needle seems to be too wide of an adjustment and takes about 1 1/2 turns past the peak to choke out the engine at high speed. After reading this posts about the holes not lining up in the fuel inlet of the carb, I took my fuel nipple out and the holes were about halfway lined up. I drilled it out, driiled the fuel nipples on the remote and drilled the muffler nipple as well. I have not ran my engine yet, but I went to my friend's house and told him about this thread. He checked his and his were not lined up either. He drilled only his brass inlet in the carb, no nipples. After a little tweaking, his engine runs mugh better ( on the ground), with only very slight hesitation in transition from low to high.( could be slow throttle servo?) . Looks like the problem has mainly been solved in thanks to the people here. Several people told me to box it up and send it back ( Tower Hobbies). Maybe I would have done just that if I thought it would make it all the way back to China! ( I wonder if there are as many ships heading back to China as there are Coming from China?) The stuff(junk) from China never seems to fit quite right, or am I the ONLY person who has ever had that problem? ( I get tired of hearing that answer from company techs!) I must be what you would call a " Pioneer of Problems"! Now if I can get the rake handle to stay on my new Chinese yard rake, but thats a different forum.


THANKS to all of you in this thread!
KE4MIZ

Hi Yoyo27983,

Glad to hear you got it running OK and we could help.

As for the carburettor and the transition adjustment, you may want to check posts number 38 and 76 in this thread. If you follow post number 38, and adjust both HSN (high speed needle) and LSN (low speed needle) at WOT (wide open throtle), you should only need to fine tune the LSN about 1/8 turn either way to get a good transition.

One thing that I have noticed on another engine is: normally when I poke full throttle, and the engine hesitates, I expect the LSN needs to go in (leaner) just a bit - on this engine I had to turn the needle out (richer) about 1/16th of a turn. I found this strange, and contrary to what I expected.

Note: Once you have the engine running well at WOT with both the LSN and HSN adjusted, the LSN is very touchy and needs very little adjustment at low speed - no more than an 1/8th of a turn. If you need a starting point - carefully tighten the needle valves in until they just stop - DO NOT tighten with pressure. Then back out the number of turns shown in post 38 - this is a good starting point.

I should also note that I use Fox RC Idle Bar Long glow plugs - they are reasonably priced and work very well in all my engines, no matter what brand of engine and I have several. I also use 15 percent nitro and always check the fuel labels to make sure there is castrol oil in the fuel.

Thanks for your feed back, if you do get your transition problem fixed, would you let us know how you got it fixed?

Fly4Fun,

Wayne

Wayne,

These motors love 15% nitro, and a little extra castor ain't gonna hurt none either. I don't agree, however, with running a "idle bar" plug in these. I'm glad you've had good luck with them, but if you ever saw a motor where the idle bar came loose and separated from the plug, you'd probably change. [X(] It's amazing the kind of damage they can do for being so small!

I went and checked the dry lake where we fly, and....well....let's just say it's not "dry". I may fly at another field here shortly, as I think I'm starting to go thru withdrawals!

I have a plane I'm trying to finish up, so as soon as that's done I'll be tackling the 47's I have.

Gary

Hi Gary,

I hope your able to get out flying soon. I can identify with your withdrawal - its -5 here today and I haven't been out for a while.

As for the idle bar, the Fox has the plug machined as one piece with the idle bar machined as part of the plug, they can not come off. I've seen some other plugs that had the idle bar "tacked" in place with weld and have seen one of these come loose - I agree they do a lot of damage.

If you use an idle bar plug, make sure you use a Fox plug.

I look forward to hearing how you make out with your GMS .47's.

Thanks for your comments.

Fly4Fun,

Wayne

hi Wayne, I ran my engine yesterday after drilling the nipples and carb. I found that the high speed needle could be turned about 2 turns past the peak before it started to choke. the low speed seem to adjust ok going from rich to lean in about 1/4 turn. I could tell by the threads on the high needle , it was further out than before. I first tuned the high speed by lifting the nose to 45degrees and tuning just past peak. then quickly return the throttle to a high idle and tune the low just rich of the peak, also tested using the pinch method. The transition is ok if I don't let it idle very long and then slowly transition into full throttle.I think that what is happening here is that 1. then engine starts collecting fuel in the crankcase when it is returned to a less than full throttle position. 2. then engine starts cooling off when idlingand when it gets below about 250 degrees at the plug, it starts to run ragged and loose rpm until it dies. If I idle too long, or throttle up too fast, then it just dies. I did notice that after idling about 15 seconds, then throttle up, there is a small air bubble in the fuel line between the remote needle and the carb. Could this be a air leak at the remote needle? I didn't see it on the tank side of the needle. I am at a loss now as to what to do next. Try some srceen in the muffler to add more back pressure and try to seal up the needle valve.

Yoyo27983

Hi Yoyo27983,

I really haven't worked with the RNV (rear needle valve) assemblies too much and so I'm not very knowledgable, perhaps someone else can jump in and help us out here. I'll give you my thoughts and I hope they help.

If there is never air in the line from the tank, to the RNV but air appears between the RNV and the carb, then I would suspect an air leak, probably around the needle valve itself ("O" ring?) or one of the fittings.

The GMS .47 has had air leaks around the carb and backplate and this may cause idling and mixture problems. There may be a little air leaking out the front bearing, and this is normal.

To test:
1. Remove the muffler and put about 1 foot fuel line onto the rear needle valve intake nipple.
2. Back out the rear needle valve to get reasonble air flow (about one turn open from normal flying), open the carb fully, put your thumb or finger over the carb opening (throat) and block the exhaust opening with another thumb/finger.
3. Blow into the fuel line and listen for any air leaks. To isolate leaks, either spray area with soapy water (or carefully partially submerge in water - don't let water in the carb or exhaust opening - if you do - dry thouroughly and re-lubricate) and look for bubbles.

If the carb body is leaking where it goes into the crankcase, or the the back plate is leaking, it can be sealed with a small amount of RTV (room temperature vulcanization) such as Permatex Ultra Copper or something similar when you reinstall. It is like silicon sealer, will take heat and usually available at the local auto parts store.

Hope this helps.

Fly4Fun,

Wayne Miller

I've got mine ready to fire up, it went on this Sonic Q-500 plane
for club racing. Idrilled the fuel inlet into the spraybar, I haven't
drilled the fuel inlet nipple. I did drill the muffler pressure nipple.
I blew through it with a piece of line, and it seemed to be a tad
restrictive. I drilled it with a #50 wire drill.

I massaged the motor and carb, lock-titeing the muffler. I have a
MAS 9 1/2-6 on it for now, it should spin-up nicely on 15%
PowerMaster fuel. I'll probably end up with a 9-7, or 9-8 on it.

FBD.

Hi FlyBoyDave,

It looks like it will scream, let us know how it goes.

Fly4Fun,

Wayne

Just wanted to throw in a comment here. It has been too cold here for me to test XJET's information about using smaller holes in the exhaust nipple to maintain tank pressure. I too have seen air bubbles in the line during transition. Since the engine I am working with is a front needle carb, the bubbles are likely coming from an improperly pressurized tank. I just want to make sure everyone doesn't drill out these nipples, until we see what effect a smaller hole has on keeping the tank from depressurizing. XJET's comments make a lot of sense to me. Good luck Guy's!

Andy

Well, I wound mine up today....I pre-heated the engine to remove the pinch.
I had also pre-oiled the piston with some straight castor. I ran it for three
shorts runs, a few minutes each....full throttle, working the needle in and
out between peak and rich.

On the third run I wound it up....I had seen 16,000 even, but this time I
wound it up, and quickly took a pic, so I could richen it back up. I was
cranking 16, 200 as you can see, a real screamer. I tached it at my rich
setting (cool running) and it was turning 15.5 to 15.6.

I had to open the low speed 1/4 turn, it was bogging coming up off idle,
now the transition is crisp. I am very pleased with the way it ran, and spun up.

Not bad for $65.00 !!!

FBD.

Hi FlyBoyDave,

Great pictures! I'm glad that another GMS .47 is "off the shelf"!

If opening the low speed needle a little (richer) stopped the bogging during transition, it is the same as I had experienced with another GMS .47 engine. Previously, I would have thought it would have to be turned in a little (leaner).

Thanks for the report, just for your information, I'll be out of town next week, and out of touch - so I won't be able to respond to any emails.

I like planes that are fast, "goove" well, and are able to slow down for landings. I may look at one like yours. Let me know how it flys.

Fly4Fun,

Wayne