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PS
Joined: 08 Sep 2006
Posts: 84
Location: Texas
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 Posted: Sun Oct 04, 2009 4:16 pm Post subject: Engine Surge |
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Any ideas of what could cause an engine surge at takeoff power which led to an aborted takeoff. The rpm fluctuated between 85-100%, all run up checks were normal. The prop gov is new, so gov issues are hopefully eliminated. Could this be a carb issue, maybe a bad diaphram, supercharger, or maybe a mag coil? This aircraft had this problem some time ago and was parked.
All help is appreciated,
Phil
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dsavarese0812(at)bellsout
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| Posted: Mon Oct 05, 2009 5:18 am Post subject: Engine Surge |
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Phil,
I seriously doubt it is a mag coil problem. If it is not the prop governor, then I would suspect a fuel problem. Have you checked all the fuel screens including the finger screen in the back of the carburetor? It's the one just above the 90 degree fuel inlet elbow (on a Yak 52); a 22 mm nut. Check this finger screen. Were the hoses, particularly the fuel hoses, replaced? It is possible there is a "flapper" in one of the two fuel hoses; the one from the coarse fuel screen to the fuel pump and the one from the fine fuel screen to the carburetor.
We recently changed a carburetor diaphragm on a Yak 50 with a surging problem at higher power settings. Although I could not find any cracks in the diaphragm, the problem went away. Look at the bottom center of the barometric chamber. There is a small bolt with multiple holes in it. This is a breather plug for the barometric chamber. I have found evidence of fuel leakage on the head of this small bolt. It had dark brown corrosion around it. On one plug there was very slight fuel drips. This means the plate is loose around the diaphragm and is leaking fuel into the barometric chamber. If fuel leak out, there can also be an air leak. So check this as well as this could have easily been the problem on the Yak 50.
If you decide to change the diaphragm, Mark Jefferies in the UK is having them made. If I am not mistaken, they are about 75 GBP, plus shipping of course.
Let me know what you find.
Dennis
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