Well; I've a GMS 1.20 which runs perfectly... until suddenly stops!!!!
According to the sound, seems that fuel flow stops but there is no reason that I can find. Both pressure line and fuel line are perfect, carburator is totally tight and is not running lean. Propeller is 16x6. Iddle neddle is also well calibrated for good transition...
Can anybody tell me where to start looking for what causes the shut out (before I smash it with a hammer)? PLEASE!!!!!!!!

Have you checked the fuel tank and clunk ? Pull the tank and, after disassembly of the tank, THOROUGHLY clean the inside of the tank AND the end of the clunk. While you have the tank out you might as well replace the lines inside the tank also.

All you need is a small piece of junk in the tank. It floats around, then hits the end of the clunk. No fuel to the engine. Engine suddenly stops, but you have plenty of fuel. With the muffler pressure off the tank and the engine not drawing, the piece of junk floats off the end of the clunk and the engine runs again, until the same scenario is repeated.

how long does it run before stopping?does it run the same amount of time or use the same amount of fuel each time?

The running time varies... I had 3 min as well 10 min before stops...
I going to check then tank, but it's new so I don't believe the problem is the tank...
Thanks for your answers; I'll wait for more
Regards!!!!

I suspect you’ll find the problem in the tank. Brand new = possible chunk of plastic from the molding process floating around; or something was stuck to the clunk or fuel line and got inside the tank when you assembled it.

My brother had a new plane that developed similar symptoms. It was fine the first couple of trips to the field, then started the deal where it would run fine for a few minutes then die. He was tuning the engine every way possible and the problem wouldn’t go away. Someone suggested taking the tank apart and he was positive that it must be something else because the tank and everything in it was new. He finally pulled the tank and found the clunk had fallen off the end of the fuel line and was just rolling around in the tank. When the loose end of the line floated above the fuel level it ‘ran out of fuel’ and died. Put it back on, secured it with a tie wrap, now it runs fine again.

Anything can foul a fuel line... the smallest thing that I have seen is a piece of fluff from a dandelion.

It was invisible and allowed a bit of fuel flow - once you accelerated the extra pull compressed the fluff and shut down the free flow of fuel.

Now that was hard to find... bottom line - anything can happen - check the tank!

Something floating in the tank that plugs ups the fuel line- That is a good thought; I can see that happening pretty easily...

If that is not the problem though, have you tried different (brand new) fuel or a different glow plug? I have seen engine problems caused by trying to use old fuel. Or even the brand or type of fuel. Some engines are fussy about the percent of nitro or the type of oil in the fuel. And some engines work better with certain brands or types of glowplugs too. I once had an engine that wouldn't run worth a darn until I put a K&B idle-bar plug in it. Pretty much all I use now are the OS #8 for 2-strokes and the type F for 4-strokes. Might take a bit of experimentation to find what works. Good luck!

Well; the tank is already clean and problem continues...
Any other ideas?

Hi!
Sounds if you run it too lean...are you sure you don't?
Have you checked the needle housing for dirt inside it?
I once had a .40 Blue Bird engine that behaved strangely and finally discovered that a small piece of brass was floating around inside the high speed needle assembly.

Regards!
Jan K

Did you check the metal lines in the tank for cracks? They can crack and cause weird problems. Go over the engine for loose bolts-a loose backplate can also cause weird symptoms. Fresh fuel and a fresh glow plug can't hurt, either. And it could be a little lean and/or not quite broken in, if it's new.

mmmmmmmm...
Jan; is not running lean, the first suspect was this and the failure showed even working with high needle very opened.
Next step: what you said: Major surjery looking for small dirts into the carb/lines or whatever.
The engine is new but already burned about 4 to 5 gallons...
Could the problem be realted with an undersized propeller? I'm still spining the breaker 16x6 where the manufacturer reccomends 16x8 to 18x8. (to be sincere; I don't believe the problem is that but I do'nt neither know what to believe or not at this time...)
Thanks; hope to hear more ideas
Guille

There's a thread going about a Super Tigre G2300 that only likes one prop. When the owner switches to a smaller prop the engine runs for a while then quits. I have no idea if the small prop could be the problem but I'd definitely try to get one that's in the recommended range and try it.

From http://www2.towerhobbies.com/cgi-bin...?&I=LXDXM5&P=0
Suggested Prop:
Sport 16x10
Racing 16x8
Scale 18x5, 18x6

If the engine is hot and not run lean then I would say the prop is too small and the engine revs too fast. But I usually don't know what I'm talking about...Had a OS FP-40 that would run hot and dead stick with a 10X6, went to a 10X5 and solved the problem. If you bought the engine from Mecoa or Tower, ask them, couldn't hurt. I just realized that the FP-40 problem is opposite from your problem, but I've heard that too small a prop wpould cause overheating just as a prop that taxes the engine would.

Hi!
The prop is definitely not too small, to the contrary it might be a little too large. I would try a 15x6 first.And do try an OS 8 and Enya 3 glowplug.
Do you have the tank mounted right? Tank size?

Regards!
Jan K
Sweden

Tank is 500 cc and it's properly installed (1 line to carb; 1 line to pressure; 1 line to normally closed charge valve). I've tried the complete system and no air leak was detected... (so it's good). Also, tank's medium line is at the same heigh of carb.

I have seen some crazy things with engines. Do it in steps. You have already started with the tank, not it. Moved on to the lines, not it. fuel nipple next. Take your high end needle out open the card and see if any fuel runs out. Something as small as a grain of sand can cause your problem in the carb. I have also seen this with a GWS 47 I had. In the end it was cylinder sleave that had moveing. I also had the same problem with a SuperTigre 2300 I mod the carb on. It was trash in the high needle. Good luck!

Freebird

I had the exact problem your talking about with a smaller GMS engine. and was becoming the king of deadstiks. I installed a K&B glow plug with an idle bar and I've got at least 75 flights on it and it hasn,t so much as coughed once. It made such a difference it was unbelievable, My GMS also had an appointment with a hammer until this was discovered.



Ken

Thanks a lot to all; this weekend I'll try the new glow plug and I'll tell you if it worked or not. BTW; I'm still woth the manufacturer's installed glow plug.
Rregards!!!!!
Guille

Well; test in last weekend resulted negative: Glow plug was not he problem since I tried a OS.8 and a K&B with bar and sudden stop continued... But: I realised the the head of cilinder was too hot, so: Do I have to think that the problem is a small propeller? I can ensure that I was not running lean (nice smoke!!!).
Another sympthom: I calibrated the engine perfectly on high and low; when came the moment of testing "nose up" the high working regime was nicely sustained; when I lowed the trottle (keeping the nose up atitude) and tried to accelerate again sudden stop showed up!!!!! Do I Have to think that the muffler (bisson pitts) does ot pressures the tank properly?
Thanks again
Guille

Did you find your problem? I would say it not the bission muffler. You can lose a little off of the pipes and still get good presure and gain RPM on the high side. if you are still have the problem, look at the head sleave. Make sure it is lined up and not tilted.

Everybody has come up with all good reasons for an engine quitting. There are so many things that can cause it. I myself went through the same aggrevation when I tried using up 3 year old fuel. Some was even 10 years. Old fuel has had a chance to absorb moisture from the air, not to mention the nitro become very unstable and dangerous with very old fuel. My engine would tune fine on the ground, take off and fly for a while, and then suddenly dead stick. New fuel cured that problem totally. Obviously you're probably using fresh fuel. Another thing you may want to consider is using a fuel pump. It's possible the whole setup you have, while functionally okay, may not be supplying enough fuel at high throttle. You can test this by attaching a squeeze bulb to your pressure line, run the engine, especially pointed up, and have someone hold pressure on the squeeze bulb. Tune the engine and throttle it up. If it stays running, good. Then put the pressure line back on the muffler and check again for quitting. If it does, then fuel flow would be a likely candidate. These are just a couple of ideas. Might help, might not. Good luck trouble shooting that problem.

p.s. Those Enya glow plugs are awesome and I have cured many problems just using them. They are not cheap, but worth it.

Just something to throw into the mix here, I have an MDS .48 that was suddenly stopping on every flight. I went through similar troubleshooting. Just as I was about to give up and call it a bum engine, I discovered that the head bolts were not tight. It came that way from the manufacturer. I tightened them and the engine has been fantastic ever since.

Easy to check.

Good News to all!!!!!!!!!!!!!!!
Found the problems!!!!!!!!!!!!!!
and the winner is................................................ ....................PROPELLER!!!!
I analysed the otto cycle graphic taking into account tah the cilinder head was really HOT. So I considered it as an energy loose on the graphic. This caused two occurrencies: 1- Excesive heat did not allowed a proper combustion (due to evaporation or compression loose or whatever) and 2- since the torque is directly related with pressure above the piston (and thus the muffler), with a small prop there were not enough pressure available for the tank.
As a conclusion to be taken into account: If the engine gets really hot (even if doesn't quit) a larger propeller is recommended to be used.
Anecdotically; I met a guy who had the same problem with a Supertigre 2300 (can you believe it? one of the most trustable engines ever built)... same simptoms than my GMS120; he also tried EVERYTHING in order to get an acceptable running and solution was as simple as: CHANGE THE PROP.
Well guys; I really appreciate your answers and I hope this thread served to anybody!!!! WORKED FOR ME!!!!!!
Best regards; thanks
Guille

What prop did you find worked best for you?
I have 3D Mayhem that almost works great. When i point it up and try to hover the GMS 120 gives me a little trouble.

Yes; I could solve the prblem with my gms with a 16x10 propeller for pattern... but in the same manner than you he 120 uses to give some problem. I believe that a perry pump can entirely solve any quit problem. (Anyway; I've already sold the engine and bougth a Supertigre 2300: a jewel!!!)
Keep in touch!!! Good luck
Guillermo