YS .91 AC

[Ken Velez]

  Hi guys, I picked up a YS .91AC some time back. I finally got an airframe
for it, but ran into some problems and I have no clue what can be causing
it. So I figure ask the experts out there before spending money on parts not
needed. The problem is that from 1/4 power to 3/4 the engine surges, not
just a little but quite extreme. 1000 or better rpm difference and the
higher the throttle the bigger the difference. When  I first got it I took
it completely apart and inspected it, all seem good so after cleaning it I
re assembled it using a new set of o-rings, new diaphragm, plunger, spring
and actuator. The gaskets seem all right so I re used the original ones
(maybe that's the problem). What's really throwing me off is that it idles
PERFECT and I mean it will hold 1600 r's for ever and at full power is also
as expected. Compression is very good, bearings are smooth, valves
calibrated, regulator it doesn't care where it is. I have tried full out to
all the way in. It seems not to change much (currently it is flush with the
case). So what's happening in the middle? It's got me baffled. Thanks in
advance.

Ken Velez

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