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HomeAircraftHelicopterHelicopter Main Discussion › OS50 sx-h runs at 1/2 on needle
12-05-2012 02:38 AM  5 years agoPost 1
flyinfriend

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North American continent

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I posted on this issue a week or two ago. Since then I switched out the carb on my 55 hyper to see if it made any difference. It still only runs right at about half out on the high needle. Any more open and it won't get past 1/2 stick and spool up, it will just blurble rich and then die. If I'm just slightly richer than the 'sweet' spot (where it will actually run)it will start spooling up and just dead quit. If I lean it 1 or 2 clicks then it spools up and runs fine. I shot temps at the base of the head at around 204F after just flying around.

I don't understand why it runs blubbery rich and dies at any more than 1/2 open on the high needle. I have the low needle set just a bit lean of the 12 o'clock position as set from the factory.

This makes no sense to me and runs the same with two different carbs.
Does anyone have any ideas. This is driving me nuts. If I lean it for any power it will be slightly under 1/2 turn out.

One thing I forgot to mention: I am running 15% nitro and it is 2 years old but newly opened. Does nitromethane degrade and could the low nitro content be the reason I need to set it so lean?

Thanks

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12-05-2012 03:27 AM  5 years agoPost 2
John Krebs

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Pittsburgh, PA

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Well you've ruled out anything to do with the carb. I had 3 cases fuel that sat for three years and still ran fine. The jugs were all in the original boxes and the boxes where in a dark basement so sun light didn't get to the fuel either. But I would try a fresh gallon just to rule that out. Are you sure you are not too lean?

This what I would do. Double check your pitch and throttle curves.
Turn off the governor if you are using one.
Set the needles to the factory settings shown below.
Check the pressure line for splits or holes.
Get some fresh fuel.
Try and start the engine. If you get is started lean it just enough to get it to fly. It shouldn't take that much.

Carburetor Settings: (From Tower Hobbies site)
High Speed Needle Valve, Two turns open from fully closed
Idle Mixture Control Screw, Factory set-do not adjust
Medium Speed Needle Valve, Two turns open from fully closed

Good Luck
John

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12-05-2012 11:17 AM  5 years agoPost 3
Jeff polisena

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westpalmbeachflorida usa

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What pipe ? I've had align pipes cause this
Try a different one if you have it

I stole it ,flew it and gave it back ;)

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12-05-2012 03:37 PM  5 years agoPost 4
MartyH

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USA

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Change pipe, change fuel to something known to be fresh. 2 turns out of the high speed sounds rich to me. I have found I need to go considerably leaner on the highspeed than the "published" needle setting. That is just a starting point when firing up a brand new engine for the first time. It's a very rich, very conservative setting and probably not one you will want to fly on.

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12-05-2012 04:19 PM  5 years agoPost 5
flyinfriend

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North American continent

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Thanks for all of the replies.

Just some additional info:

I'm not running a governor.

The muffler is just a stock muffler that came with my Audacity Pantera from 3 yrs back. I wish I had another muffler to try but I don't. Might have to order one along with new fuel. I might see if I can bolt on an airplane muffler just to test.

My carb is a single main needle w/screw low end (stock os-55 hyper)

My pitch curves are linear with -10 and + 10

My throttle curves started out linear and have been modified only slightly to maintain reasonable head speed.

If I set the high needle to slightly richer over 1/2 it won't have any power, won't transition without shutting down all blubbery, or if it does transition the rpm won't enough to get off the ground.

The low screw is barely leaner than factory setting, maybe 12:30 from in-line with the carb barrel.

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12-05-2012 05:19 PM  5 years agoPost 6
YSRRider

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usa

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Is there an oversize pressure nipple on the pipe that is pressurizing the fuel more? Could be forcing fuel into the carb more than it needs too.

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12-05-2012 06:14 PM  5 years agoPost 7
Jeff polisena

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westpalmbeachflorida usa

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1 to 1 1/4 turns is close , I would try pipe might not be letting motor breath .

I stole it ,flew it and gave it back ;)

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12-05-2012 08:37 PM  5 years agoPost 8
MOZENZ

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Denby Dale UK

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This sounds like the muffler is blocked with carbon/unburned residue. Remove exhaust muffler and try blowing through main outlet. Not presure nipple.

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12-06-2012 01:32 AM  5 years agoPost 9
flyinfriend

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North American continent

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I removed the muffler and went to put on my plank muffler and noticed that the muffler port that bolts to the engine was really quite small compared to my os plank muffler. The no-name muffler port is 19mm the os plank muffler is 28mm. Not sure if that would make a difference but I'll have a chance to try it on Friday.

The muffler sticks straight up but at least I can test it.

Thanks again for the help.

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12-06-2012 02:59 AM  5 years agoPost 10
YSRRider

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usa

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That could be the problem. If its restricted its pressurizing the fuel more.

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01-05-2013 11:30 PM  5 years agoPost 11
YSRRider

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usa

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Was this problem ever resolved? curious..........

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01-06-2013 02:20 AM  5 years agoPost 12
flyinfriend

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North American continent

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Hi YSRRIDER,

Thanks for checking in. Trying to use the upright plank muffler didn't work out. There was fuel collecting in it. I have new plugs to try now but haven't had a chance to fly lately...too cold for me.

I need to get a new muffler to really try it out although I am doubtful that the muffler I have would make that much difference.

I have another os50 hyper that I am going to drop into the heli and try with the no-name muffler to see if that also tunes at 1/2 needle out.

I have never had an issue in the past where an engine just seemed to be running so incredibly rich until leaned to 1/2 turn out on the needle.

I will update this post when I can fly again.

Thanks again YSRRIDER,

Tom

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