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Help with An OS.46SF-P

Old 02-11-2008, 09:56 AM
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Default Help with An OS.46SF-P

Bought this engine new years ago and have never been able to get it to run truly reliably.
Was this engine made to run full flat out all the time? Wanted to use it in a 3D profile plane. Actually mounted it in the plane and same as always can't seem to get it to run properly to save my life.
Tried using the manual recommended #8 OS glow plug . No good. Used a hotter plug and that seems to at least keep it running.
Runs well at full throttle, takes forever to drop down to an idle though and just will not transition up smoothly unless I really make the throttle creap up no matter where I set the low speed mixture.
Am using a tuned pipe/header with it and running it on 15%
Am I better off using a stock OS muffler? Or something like a Macs muffler?

By the way. I completely took the carb apart, cleaned it just to make sure there was no varnish plugging it anywhere. Needle looks perfect too.
Old 02-12-2008, 12:13 PM
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Default RE: Help with An OS.46SF-P

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.
Old 02-12-2008, 12:23 PM
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Default RE: Help with An OS.46SF-P

Bill,
Thanks for the info.
Still have some unanswered questions though. Hopefully you have the answers.

Was this engine designed strictly for high speed running and not a good choice for a 3D plane?

Should I be running a tuned pipe or the stock 873 muffler that fits the standard .46 SF

Thanks,
Steve
Old 02-13-2008, 10:48 AM
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Default RE: Help with An OS.46SF-P

The pumped engine was intended for Pattern-type flying, and came out before 3D-type flying became popular. The engine will run best if it's propped to just below 13,000 RPM on the ground and leaned as detailed above. We'd use a 10 x 7 prop or so.
Old 02-13-2008, 09:32 PM
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Default RE: Help with An OS.46SF-P

Bill,
Got the engine running a pretty well using an OS A3 plug , but still not exactly running up as smoothly as I would think it needs to for 3D. Jogging the throttle I mean. Runs great if you slowly run it straight to full throttle.

I have an older but brand new made in Italy Super Tiger GS.45 abc with the stock muffler.
Would this be a better choice for a 3D plane than the .46SF-P?

I know you said the OS was really designed for Pattern flying which I'm really not familiar with so have no idea how they like their engines to run. If you could explain a little better I'd appreciate it as I would really like to put this engine into something that it'll fly well.
Old 02-14-2008, 10:33 AM
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Default RE: Help with An OS.46SF-P

"Pattern" flying is aerobatic flying that conforms to the FAI-type pattern of maneuvers. They do absolutely NO type of flying that could be called "3D". Throttle movements are generally slow and smooth, and the goal of the flight is smoothness as you fly from maneuver to maneuver. The goal is to fly each maneuver with absolute precision and timing, with smooth flow between the maneuvers.

If your engine will idle well, transition well to full throttle, and then do the reverse, as well as run properly in the midrange, then it's operating as it's supposed to operate. It may not respond well to "bang, bang" throttle movement. IF you move the throttle smoothly and the engine responds, then it's correct.

The SuperTigre may be better, but still could be a bit rich in midrange with a slight stumble when you bang the throttle around.

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