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Engines and Mufflers Having problems or need advice on Engines or Mufflers?


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Old 12-18-2012, 12:59 PM   #1
flyinfriend
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Default os50 hyper won't run until 1/2 turn out on needle

I posted this in the engines forum but thought it might get more visibility here... I am having an issue where my 0S50 hyper will only run about half out on the main needle. Much over than 1/2 turns out and it is so rich that it dies at transition. A small amount above 1/2 and it has no power. It runs consistently at 1/2 out although I know that is crazy. I can keep my finger on the back plate for about 4-5 seconds without pain. It doesn't seem to be running too hot.

I have tried two carbs (both hyper 50 carbs) and two different bottles of fuel, one is 15% and the other is 30% nitro. Both had the same behavior in that I had no power and no transition until 1/2 turn out on the main needle. I checked the needle of both carbs and there is no damage and no obstruction. I would rather be more accurate by measuring temps. I have a temp gun but not sure where to measure temps and what they should be in relationship to the location on the head.

The only other option to try is a different muffler. The one I am using is a no-name muffler. I don't have another muffler to use at the moment. Could any muffler cause this?

Thanks for any ideas.
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Old 12-18-2012, 01:19 PM   #2
ahahn
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Assuming that the needle is the correct one for that carb, the only thing that comes to mind is that the muffler is too restrictive, and as a result is supplying too much pressure to the tank.

I am not familiar with that engine, but have used glow engines a lot.

Just checked the TowerHobbies page--I note they claim the engine runs with the needle at 1 1/2 turns out.
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Old 12-18-2012, 01:31 PM   #3
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I found this picture on the net and placed a red line on it to show you where i take the temp reading on mine, I think anywhere from 180 - 210 is acceptable, Mine runs at 180 at 1 1/2 turns out with the Low needle at its default position.
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Old 12-18-2012, 01:37 PM   #4
flyinfriend
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Thanks guys and thanks for the pic. I'll try taking the temps from there, very helpful.

The needle is the one that came with the carb and I checked the o-rings on the needle to confirm they were intact. I know it should be running at about 1 1/2 and that's what has me worried about running it at 1/2 turn out. It just doesn't make any sense to me.

Thanks,

Tom
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Old 12-18-2012, 01:59 PM   #5
ahahn
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Quote:
Originally Posted by flyinfriend View Post
Thanks guys and thanks for the pic. I'll try taking the temps from there, very helpful.

The needle is the one that came with the carb and I checked the o-rings on the needle to confirm they were intact. I know it should be running at about 1 1/2 and that's what has me worried about running it at 1/2 turn out. It just doesn't make any sense to me.

Thanks,

Tom
Like I said, it is possible your muffler is too restrictive----what is (are) the size of the output hole(s). (This is a muffler-pressure setup, isn't it?)

There is another possibility and that is the seat (where the needle actually restricts the fuel flow) is damaged. However you said two carbs had the same problem, so I think it isn't that, but an overpressure problem.

Bad o-rings cause the opposite problem, too lean (air leaks in the needle) causing you to have the needle way out to get a rich enough mixture.
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Old 12-18-2012, 02:12 PM   #6
flyinfriend
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Thanks ahaan. It is a muffler pressure setup. The actual port opening on the no-name muffler toward the engine is smaller than the engine exhaust port itself by about 9mm. My plank muffler has the same opening as the engine port size it mates with. I'm not sure of the output hole. Based on what you said though if the muffler to engine port size isn't the same (muffler considerably smaller) then that may be the issue.

Thanks also for clearing up the o-ring question. I had thought bad o-rings would let more fuel by but your explanation makes sense to me.
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Old 12-18-2012, 02:22 PM   #7
ahahn
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Not matching the engine exhaust port to the muffler port inlet will restrict the engine power (potentially), but shouldn't cause the overpressure in my opinion.

The overpressure would occur because the exhaust gases cannot exit the muffler fast enough (because the output side of the muffler is too small), and as a result the fuel tank will overpressure. This overpressure forces fuel into the carb at a higher than normal pressure, which you end up "fixing" by screwing the needle in.

My guess is that your problem is the muffler, it may not be a 50 sized muffler. I haven't run a nitro heli now for about 15 years, so I am not sure what is available. Your 50 is probably about the size of an older 40 engine, which might be the size of your muffler (and why you can attach it to the engine).

As a side point, make sure there isn't any obstruction to the exit side of the muffler! It has happened in the past!

Maybe ask what mufflers others are using on this engine to get an idea what is considered "normal".

Of course the muffler might be ok and it is something else, but best to see what others are using.
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