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OS61SF ABC Pumped Won't Idle

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Old 07-11-2011, 11:52 AM
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alaflyer
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Default OS61SF ABC Pumped Won't Idle

I recently aquired used OS SF61 ABC with the PD-02 pump and the Type 86 carb. The engine starts and runs good. It will turn a 11-7 1/2 RevUp at 12,500 and a 12-10 APC at 10,400 on the stock mufler. I am having difficulty getting a reliable idle. The engine surges and eventually dies if I try to idle below 5,000 rpms. I have all the original manuals and have tried to adjust the Mixture Control Screw (very slight amounts at a time), but with no success.

All the fuel lines are hooked up correctly and there does not appear to be any leaks. The needle valve tunes normally at the top end, but it just won't idle. Any suggestions? I want to use this engine with a tuned pipe in a 70's pattern plane I am restoring (Phoenix 6), but I need to get a reliable idle before I start tuning the pipe.
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Old 07-11-2011, 12:25 PM
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Jim Oliver
 
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Default RE: OS61SF ABC Pumped Won't Idle

No help with your idle problem, but I'm just north of Prattville-are you a RAMM member?

Cheers,
Jim
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Old 07-11-2011, 01:03 PM
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alaflyer
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Default RE: OS61SF ABC Pumped Won't Idle

Jim,

Have been a RAMM member for about 20 years . . .

Frank
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Old 07-11-2011, 06:53 PM
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Jim Oliver
 
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Default RE: OS61SF ABC Pumped Won't Idle

Frank,
PM sent.

Jim
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Old 07-12-2011, 05:52 AM
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Bax
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Default RE: OS61SF ABC Pumped Won't Idle

If the pump and regulator are working correctly, here's how to set up your engine:

Your O.S. Max engine with pump should be set up in a slightly different manner than a non-pumped engine. Most modelers tend to get them set with the mixture too rich.

One sign your engine's not adjusted correctly would be surging at full throttle. This almost always means it's too rich. Also, the idle may be too rich no matter what you do to the idle mixture. If the idle is leaned a lot, but it's still too rich, the high-speed needle's too rich and needs to be properly set.

To get a good setting, you need to use a tachometer. Once the engine's had enough running to accept being leaned to peak RPM, use the tachometer to lean the engine to its peak.

At full throttle, lean the engine until the RPM stops increasing. Continue to lean the engine to the first sign of RPM drop or detonation. When you get to that point, richen to the point just before you had the RPM drop or detonation and leave the needle there. DO NOT lean to peak and then richen your usual 1/4-1/2 turn.

With a good-quality fuel, the pump system will insure that the engine receives enough fuel. The regulator in the system will make sure that the mixture stays correct as you change the throttle positions. Fly the engine to see how the mixture may change as the engine unloads in the air. You may have to lean or richen slightly, depending upon how it acts. Once you've found the proper setting, you should note the change from the absolute maximum lean position. Now you have a repeatable setting for your engine.

Newer O.S. engines with pumps have a broader range for the needle setting, but you can use the same method for all of them.
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