Bmx2996

My Feedback: (1)

I bought a used .75 Super tigre engine to put in my .60 midget mustang. I install the engine and run it for a little bit then head to the field. I started it up when I got everything ready to fly and I noticed at about 75 percent it starts to deaccelreate. So I went to adjust the needle valve and.... Nothing. I turned it in and turned out almost all the way and still no rpms drop or raise. A guy came over and looked at it and said the needle valve might be the wrong one or worn to the point of no return. Does this sound about right or is there a brick to these? I have looked at the manual and other forums on adjusting and it doesn't seem to do anything because my high speed needle is useless.

jester_s1

It's hard to say without seeing your engine, but what you describe sounds like a partial obstruction in the fuel passage. It's probably at the spraybar since that's the smallest orifice the fuel has to pass through and therefore the easiest one to get clogged. The obstruction will limit how rich you can go, and so the primary symptom is an engine that runs consistently lean no matter how you turn the valve. You can probably go leaner if you want to, but not richer right? If the response to the needle is inconsistent, that's probably an air leak. Check for bad o rings, loose screws, and bad fuel lines to fix that.

ronwc

My Feedback: (404)

If you are running a pitts type muffler, plug one side of the exhaust to create higher fuel pressure.

raptureboy

The seat on the needle valve is most likely worn and not sealing correctly, or the spray bar opening has been enlaged by contantly screwing the needle down tight by the prev owner. I had the same issue with a used OS FS 90 and it took a new carb as the spray bar could not be replaced. My friend is having the same problem with his.