OS .46 SF Airplane Engine 1/3-1/4 Throttle Issues

by Jeffery
(Rockmart GA, USA)

I have recently gotten back into the hobby after about 7 years of being out due to school and such. I found a flying field close to where I live now and re-furbished my trainer plane to get myself reacclimated to the "feel" of things with the help of an experienced pilot.

Last Sunday 20 June 10 was the first time the plane was up in the air and the engine ran great after trading out a glow plug. Two flights were made on Sunday before the experienced pilot had to leave.

Well, I went back to the field last night 24 June 10 and met up with the experienced pilot, started the engine up, he took the plane off and let me have the controls. After making some simulated approaches, he had me land the plane.

On the second flight, the plane done great through 75% of the flight until I came on an approach for landing and had to abort. After increasing throttle to gain airspeed, the engine started surging but never really quit.

What is concerning is the fact that the engine runs great on the ground all the way up to full throttle. Even on the third flight, where I took off for the first time in 7 years, the engine started acting up again when throttle was reduced to 1/3 to 1/4.

Mixture is set in the "sweet spot." The experienced pilot set that for me.

Before the first flight, I had taken and replaced all the fuel lines, fuel filter, and the tank. The fuel line had some age on it but it was kept in the dark.

I am going to go through the pain staking process of removing the tank and replace the line with some "new" line, not the line I have that has been kept in the dark, and see if that makes a difference.

Before last night's flights, I put in a "brand new" OS A3 #6 Hot plug since the other plug was a used plug.

Any other suggestions or comments will be greatly appreciated.

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OS .46 SF Airplane Engine 1/3-1/4 Throttle Issues

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Jun 29, 2010
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RE: low needle
by: Jeffery

Thanks Matt for the input. I have tried to adjust the low needle and a fellow modeler has adjusted it to where he said it should be in the right setting.

The engine still just want run good anymore. I did find a split in the fuel tubing and replaced all the tubing on the plane. Inside the tank, pressure line and feed line.

The engine runs some better now but I can only get about a 3 minute flight out of it and it dies.

After replacing the fuel tubing, I took it to the field on Sunday and the first attempt at a flight resulted in a engine quit right after take off. (Had enough space to safely get the bird back on the ground). But it back fired right after slowing down and dying right after takeoff.

I believe the engine itself has seen its better flights and ready for retirement unless it is rebuilt.

I have another engine that I am going to start breaking in today (29 Jun 10) and try that hopefully by Thursday.

Thanks for the comment and help.

Jun 28, 2010
Rating

Sounds like low end needle is too rich
by: Matt

It sounds like your low end needle may be a bit lean.

The high end needle controls the engine from mid to high throttle. The low end controls the engine while it is idling and also control how the engine transitions from throttle to full throttle.

If the engine dies immediately when transitioning from idle to full throttle this is an indication that the low end needle is too lean.

If the engine studders, coughs, studders and carries on during transition this usually means the low end needle is a bit too rich.

I would try adjusting the low end.