OS 91 Surpass unreliable needle setting - RCCanada - Canada Radio Controlled Hobby Forum
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Old 08-29-2013, 08:33 AM   #1
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OS 91 Surpass unreliable needle setting

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The syptoms are as follows: The engine runs rich and when tweeking the needle valve to get better performance it will run erratic with periods of surging and rich. The needle valve is only 1/4 turn!! open from dead close and any further leaning will stop the engine.
Suggestions please. I have tried all I can think of including complete rebuild of the fuel tank system, resetting the idle sleeve, setting the valve clearances. Do I possibly have the wrong needle valve?
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Old 08-29-2013, 09:07 AM   #2
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Re: OS 91 Surpass unreliable needle setting

Try new orings on the needles.
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Old 08-29-2013, 11:54 AM   #3
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Re: OS 91 Surpass unreliable needle setting

Engine is sucking alot of air from probably the intake as well as the mixer screws.
If you keep going really lean just to keep it running the engine will be damaged.

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Old 08-29-2013, 06:00 PM   #4
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Re: OS 91 Surpass unreliable needle setting

Sounds like air in the fuel line. There is either a hole in it or the tank is vibrating. When the "O" ring on the needle goes bad the muffler pressure causes the fuel to leak out above half throttle.

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Old 08-29-2013, 07:37 PM   #5
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Re: OS 91 Surpass unreliable needle setting

Something that I have seen (that most people don't think about) is the WRONG needle valve being used.

If the engine is NEW - this is not a concern.

If you have had the engine apart for cleaning - is it possible that you mixed up needle valves? They are NOT ALL ALIKE!

Check to make sure that the needle valve is seating correctly and go from there.
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