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engine shutting down on take off

Old 05-03-2011, 03:52 AM
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hotrod31
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Default engine shutting down on take off

I have a .47 gms engine that cut off on take off when you are about 10ft off the ground it wants to stall. I have adjust the needle on the ground while holding it upright and it still acts up. The only thing i can do is cut the throttle to 1/2 and then it runs fine, or when its up to flying height then i can give it 100% throttle and as long as i don't go up to sharply it's fine. I know it's a moody engine but it's worked better on my other planes.
Old 05-03-2011, 04:16 AM
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Default RE: engine shutting down on take off

ORIGINAL: hotrod31

I have a .47 gms engine that cut off on take off when you are about 10ft off the ground it wants to stall. I have adjust the needle on the ground while holding it upright and it still acts up. The only thing i can do is cut the throttle to 1/2 and then it runs fine, or when its up to flying height then i can give it 100% throttle and as long as i don't go up to sharply it's fine. I know it's a moody engine but it's worked better on my other planes.


It sounds as if your low end is too rich. When I first started my Super Tigger .51 a few days ago, my engine did the same thing. I don't know very much about your engine, but most people in here will tell you that Super Tiggers are usually very touchy. When I slammed the throttle forward, it didn't respond quickly and it gradually went up to 100%. (Plus I noticed she smoked and spit out more oil than usual, my pant leg was soaked after running out a 8oz tank of glow.


Because my Tigger engine was on it's side I had to keep turning off the motor everytime I made a turn on the low end, and every time I did that, we have to re-adjust the top end needle. It was a pain!


Now if my Tigger engine was vertical in the mount, I usually crank the engine at 100% then bring it down to 50% and take a long wire hanger, straighten it out and beat one end with a hammer and file the tip straight- and use it to adjust your low end while your engine is running at 50%. It will go up in RPM quite a bit and if it starts to decrease in RPM when you are tightening the low end, then you went too far. Back off on it! As soon as you have that nice smooth sound, back off 1/8th of a turn. Now Throttle up and re-adjust your high end.


What I just explained to you is how to adjust your low and midrange. With a straight coat hanger, and by making a thin screw driver out of it, if you slip your wire will hit the prop and not your hand and you can get a more accurate setting besides all that.

I'm sure it will work for you. Most glow 2- stroke and 4- stroke engines run on the same principle.


Pete
Old 05-03-2011, 05:47 AM
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Edwin
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Default RE: engine shutting down on take off

Good advice. Another thing to think about is your plumbing. What does your engine mounting look like? Where is the fuel tank in relation to the center line of the carb spraybar. Rule of thumb is the tank centerline should be about 3/8" (or so) below the carb spraybar. Different engines draw fuel at different rates which can allow a little flexibility in tank placement. You might also check for pinched fuel lines during installation. Thats happened to me on more than one occasion.
Edwin
Old 05-03-2011, 08:52 AM
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Default RE: engine shutting down on take off

i think you are to lean!! If the low end was to rich it would load up soon as the throttle was advanced for take off. If the plane is right on the edge of being lean and the accelerates it is harder for the fuel to get to the engine add in the pull up and the g load increase's and further leans the engine.

the other thing that might cause this is a pinched vent line. as the fuel is with drawn from the tank no air can get in and the tank forms a vacuum and cause it to go lean.
Old 05-03-2011, 09:57 AM
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Default RE: engine shutting down on take off

I have a GMS .47 that was given to me because it ran like that. It was one of the older ones that had the mis-drilled fuel inlet bushing on the carb, and also had air leaks all over. Re-drilling the inlet via the fuel nipple and sealing everything with a healthy coat of make-a-gasket made for a great running engine. The partially blocked inlet lets it run fine at low throttle settings, or even rich, but leans it out more and more as the throttle is advanced. Remove the nipple off the carb and look at the bushing. If the hole your looking at is partially blocked at the bottom, this could be your answer.
Old 05-03-2011, 10:55 AM
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Default RE: engine shutting down on take off

Check the length of the tube in the tank holding the clunk. If it is to long and lets the clunk touch the rear of the tank, you will get the result you are seeing. The cluck hits the back of the tank and shuts off the flow of the fuel.
Old 05-03-2011, 12:00 PM
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Default RE: engine shutting down on take off


ORIGINAL: Rodney

Check the length of the tube in the tank holding the clunk. If it is to long and lets the clunk touch the rear of the tank, you will get the result you are seeing. The cluck hits the back of the tank and shuts off the flow of the fuel.
+1
Had same issues with one plane. Shortened the clunk line and all was good.

Old 05-03-2011, 12:24 PM
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Default RE: engine shutting down on take off

Most clunks have a recess in them for that reason dont they ? Similer to a flat head screw. I have not seen one without it but I couild be wrong. Either way not the ituation you wnat to have.. clunk against the tank.
Old 05-03-2011, 01:15 PM
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Default RE: engine shutting down on take off

Check your throttle cable to make sure it is secure and can not vibrate. I had a difficult problem exactly as you describe and it was the throttle cable vibrating. That causes the needle valve assembly to go back and forth, moving the needle valve in and out, which (in my case) put bubbles backward into the fuel line. I know that this sounds like a stretch, but it's worth checking out if nothing else is panning out.
Old 05-03-2011, 02:04 PM
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Default RE: engine shutting down on take off

too lean.
Old 05-03-2011, 05:20 PM
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hotrod31
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Default RE: engine shutting down on take off

thanx for all the advise, i'll try making some adjustment as soon as I can. One thing I did not mention was that I have a thunder tiger carb on it now(due the touchy adjustments even after I enlarged the fuel inlet and o.s muffler and sealed with high temp silicon). this thing is driving me crazy!
Old 05-03-2011, 06:01 PM
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Default RE: engine shutting down on take off

I agree with the members that advise a lean mix.

As I see it, when you open the throttle at full, not enough fuel flows into the Venturi of the carb, and the excess of air just suffocates the flame.
At low and medium rpm's, an extra rich adjustment of the idle helps compensate a lean high.

Check for any restriction inside the needle valve, as well as inside the nipple of the muffler from where the exhaust pressure feeds the tank.
Old 05-04-2011, 06:18 AM
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Villa
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Default RE: engine shutting down on take off

Hi hotrod31
When I had a similar problem, I suspected low muffler pressure for pushing the fuel to the carburetor. I went so far as to instal a tubing "tee" at the carburetor fuel inlet, and ran some fuel tubing vertically up, and put some fuel into it. In this way I was able to record the number of inches of fuel pressure I was getting from one engine, and compare it to another engine that was running well. Every fuel threaded connection in the fuel system must be sealed with Loctite. I also use high temp silicone sealant on the muffler flange connection along with the bearing surface of the muffler thru bolt head.
Old 05-04-2011, 06:59 AM
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Default RE: engine shutting down on take off

Hi!
Simple!
Too lean!
In some way your engine doesn't get enough fuel! Investigate why!! Most of the time it's simply just the high speed needle that is tweaked in too much!
Old 05-04-2011, 07:26 AM
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Default RE: engine shutting down on take off

I bet he's too rich.

Don't forget people I wrote that I went through the same problem a few days prior. If he sets his mid-range like I suggested it will solve a lot of issues. I also agree with Edwin about the plumbing. And Villa about the back pressure, and Rodney about the clunk. Check everything!

Also tighten down all your head allen bolts, check for any bolts or screws loose on your engine. Any air leaks will alter the way your engine runs. Check, check and if you're not sure re-check.

Remember people, the guy Posted that he's tried adjusting his high end while holding the plane straight up. That tells me that his mid-range and high end is off on the rich side as a result- over flooding his engine until he gets a glow plug drown out. Or he has plumbing issues on top of it all.

Winner takes all if he finds the problem and gets back to us. I'll admit if I'm wrong, I promise. Just don't tell my wife.


Pete
Old 05-04-2011, 09:00 AM
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hotrod31
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Default RE: engine shutting down on take off

ok, i didnt want this to become a contest but im starting to feel the pressure! lol. I agree with too rich due to the fact it doesnt seem to have full rpms when in the air and there seems to a decent smoke trail when flying and makes a huge oil mess on the plane, so i doubt it's too lean. I will try too play around with it tonight. thanx **there might be a free gms .47 to give away**
Old 05-04-2011, 09:34 AM
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Default RE: engine shutting down on take off

if it was so rich to the point the engine dies then he would never get off the ground. if rich and advance the trottle it would load up and he would abort the takeoff. adjusting the plane with the nose in the air can be a good way to set it but if trying to get every bit of rpm out of it could be lean.

the first thing i do if having engine problems is a new plug and new fuel.
then check engine for leaks. Carb, head, rear cover and so on.
then pull the tank and open it up and replace all fuel line.
replace fuel line to engine.
then try again.
i have found clunks fell off, holes in line letting air in once some fuel comes out of the tank
Old 05-04-2011, 10:37 AM
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Default RE: engine shutting down on take off

ORIGINAL: airraptor

if it was so rich to the point the engine dies then he would never get off the ground. if rich and advance the trottle it would load up and he would abort the takeoff. adjusting the plane with the nose in the air can be a good way to set it but if trying to get every bit of rpm out of it could be lean.

the first thing i do if having engine problems is a new plug and new fuel.
then check engine for leaks. Carb, head, rear cover and so on.
then pull the tank and open it up and replace all fuel line.
replace fuel line to engine.
then try again.
i have found clunks fell off, holes in line letting air in once some fuel comes out of the tank

Not necessarily, that depends on how rich the needle is set at. My engine would have got off the ground, but she would have wanted to croak or stall out on me.

ORIGINAL:hotrod31

ok, i didnt want this to become a contest but im starting to feel the pressure! lol. I agree with too rich due to the fact it doesnt seem to have full rpms when in the air and there seems to a decent smoke trail when flying and makes a huge oil mess on the plane, so i doubt it's too lean. I will try too play around with it tonight. thanx **there might be a free gms .47 to give away** ]
We are just eager to help. We might not always agree, and we aren't always right, but we all have a good heart and love the hobby and enjoy helping a fellow flyer.

A P-47? No thanks, I was hoping for that nice BUSA Fokker DVIII! Darn!

Good luck Hotrod31,


Peter
Old 05-04-2011, 12:19 PM
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hotrod31
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Default RE: engine shutting down on take off

I have had this engine in at least 4 different planes and its very moody in every plane, it's been my most unreliable engine so far. I find it easier to tune my old fow .60. We will see tonite.
Old 05-04-2011, 12:37 PM
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Default RE: engine shutting down on take off

If you would like you can send the engine to me and i will check it over for you. It just might run better than every when you get it back. Or if you would like we could work out a trade. I have 4 OS 46 engines. two of them are set up for a Jett red muffler and the other are for stock muffler or tower.

the two for the Jett mufflers turn 9x8 APC props at 17,300-17,400 and the other two turn 9x8's at 16,400-16,500 on the tower muffler.
Old 05-04-2011, 05:33 PM
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hotrod31
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Default RE: engine shutting down on take off

well gentlemen, I played with the high end and low end needles and I think I may have got it! and wow it is picky. I will find out for sure the next flight if it's good. Now whether it was too rich or lean i'm not sure, but my gut(and its a big one) and adjustments tell me-low speed was too rich and high speed too lean. Hopefully this engine will work better than it has in the past. Thanx to everyone!

Old 05-04-2011, 05:52 PM
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Default RE: engine shutting down on take off

Glad you improved the settings.

Touchy carbs may have deformation of the tip of the needle or the seat of the body, or leaky O-ring, or just some grit that interferes with a fine tunning.

These articles may help you:

http://modelenginenews.org/techniques/nva.html
Old 05-05-2011, 08:32 AM
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Default RE: engine shutting down on take off


ORIGINAL: hotrod31

well gentlemen, I played with the high end and low end needles and I think I may have got it! and wow it is picky. I will find out for sure the next flight if it's good. Now whether it was too rich or lean i'm not sure, but my gut(and its a big one) and adjustments tell me-low speed was too rich and high speed too lean. Hopefully this engine will work better than it has in the past. Thanx to everyone!

It can happen. All of them are a balancing act but once you get the magic spot you usually just have the high end to fool with if weather or props change. From winter to summer my high end requires about 4 clicks rich or lean to keep in tune. I almost never have to touch a low end needle once it is set. Our weather has warmed up again and getting back to normal so I have had to lean my engines again. To tell what engines I have or haven't tuned is pretty easy, if they are sluggish or have a big smoke trail I can pretty much guess I haven't done that one yet. I guess it would be easier to just write down what plane I have done but I'm pretty lazy. Good luck with yours.
Old 05-06-2011, 07:50 AM
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Default RE: engine shutting down on take off

Hi!
How much nitro do you use!? Some engines don't like 15 % nitro,and as a result are very finicky to run and act up constantly.
The remedy is to put in another 0,1mm head shim.

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