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Old 03-25-2008, 08:24 AM   #1
homme de fer
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Engine Issue

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Hi guys, I thought I would post an issue I'm having with a used Magnum .25 engine that I running in a bipe.

The first couple flights, the engine seemed to run fine though maybe I had it a little rich. Yesterday, it ran great on the first flight of the day. Then, on the second flight, the engine quit on me about 20 feet into the take-off. This happened 3 more times while simulating takeoff (just letting it run around the snow) but ran fine at full throttle when held in place on the ground.

I made a minor adjustment then tried the takeoff again. This time, it got off the ground but now, at max throttle, it kept alternating between high rpms and low rpms every 3 seconds. I backed off the throttle to a little over half and the rpms smoothed out, making it perfectly flyable.

Any ideas what may be causing this issue and what I need to look at to solve them?


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Old 03-25-2008, 08:34 AM   #2
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a pinhole in the fuel tubing or tank?

dirt in the needle valve?
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Old 03-25-2008, 09:33 AM   #3
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From your description it sounds like you are running the engine too lean.

Works fine on the ground, once the AC is in the air the engine unloads at high speed and cuts out. Run it at half speed and it works great...

Also you said it worked fine on the first flight - it was cooler then...

For my 'On-line' analysis... I would suggest richening up the High end setting and see what happens.

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Old 03-25-2008, 10:50 AM   #4
homme de fer
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Good analysis so far:

dirt in the needle - I considered it but it does run perfect on the ground

pinhole in the fuel system - Ironically, this was a problem for the maiden flight. It flew fine for about 5 minutes before it died. I fixed it and tested thoroughly before the second flight.

Engine too lean - could be. These engines are WAY more difficult to tune than my OS engines. Also, your observation that it cuts out as it unloads is spot on.

The first flight took place on Saturday; it was around -6 and windy. The second and third flight was yesterday (around -1) and I let the engine warm up for over a minute before bringing it to the flightline.

Thanks for the input.
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Old 03-25-2008, 03:26 PM   #5
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After your last good flight did you have any kind of a rough landing or perhaps thump into a snow bank? I was thinking that perhaps the fuel tank clunk has jammed forward partially kinking the clunk line. If thats the case, it would make it run irratically or run for a bit and sputter.

Just something else to consider. Hold the plane nose up and give it a bit of a shake to release the clunk...worth a try!
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