radiopicture
Joined: 23 Jun 2008
Posts: 263
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 Posted: Sat Mar 21, 2009 2:13 pm Post subject: Yak-52 power surge on takeoff |
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I have a recently purchased 1993 Yak-52 with very low total time (approximately 20 hours). A mechanic prepared the airplane for ferrying and then ferried it home for me (over 1000 miles). On the first flight (and each subsequent flight), there has been a pulsing sort of power surge. During warm-up and run-up everything is nominal, including fuel pressure (.4 or so). However, several seconds into the takeoff roll, the surging begins which manifests itself as a variation between 100% and 97% about once per second or so. The fuel pressure at that time has dropped to about .2 instead of the normal .4 or .5. Once the power is reduced (to say, 82%) it all smoothes out.
The first impression was that there was something wrong with the prop or governor. The prop was greased, seals replaced, oil delivery tube gasket was replaced, and the governor was bench tested. The problem remained.
We then decided that the problem must be fuel related. All fuel filters are clean. The fuel tank vents are unobstructed. It has been suggested that if there is even a tiny leak in the fuel system, that the bubbler can suck in enough air so that the fuel pump can't keep up with it. I was suspicious of the square o-ring on the course fuel filter, and it was replaced.
I haven't changed the pressure adjustment on the end of the fuel pump yet. It has also been suggested that if the carb is somehow improperly adjusted, it could demand too much fuel and the fuel pump cannot keep up with the demand (say, above 40 gph). I'm sort of reluctant to start messing with the factory settings on a plane with such low total time. I suppose there is still some possibility of a partial fuel line obstruction including a hose flapper or what have you.
Does anyone have any ideas about this? Thanks.
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