fuel filter puzzle

[Earl Vincent]

I would like to share an interesting problem, one I unknowingly created that cost me an entire afternoon of flying yesterday.
after some modifications to my Temptation cheek cowls, I moved my Sullivan crab trap fuel filter from a position I have used
them in for years, between the pump and carb with never a problem, to before the inlet of the fuel pump thinking to stop any
junk from entering the pump. I had changed a number of things, tank, vent line etc. so isolating this was difficult. On midrange
throttle after a prolonged idle, the engine(Webra 145) would almost shut off and then catch and be fine on the top end, it was
driving me nuts, coming out of a corner go half stick to start slow roll, sounded like engine quit, after a number of passes and
trying it after 3 turn spin it was ok but anytime a long straight line power off the hesitation would occur. So the next time it happened, I shut the motor down and landed. This was after about 10 take off and landings making adjustments to the midrange
and high speed needles. I was inspecting for the normal stuff, clunk in the tank, hole in a fuel line, etc. when I noticed large air
bubbles in the line from the pump to the carb. I started back tracking the things I had changed because this was a new problem
Changing the fuel filter back to between the pump and carb fixed the problem, I guess it worked as a air chamber and was making the pump loose its prime. moral of the story, if it ain't broke, leave it the hell alone!
 
Oh while I am typing, a Greves pipe on OS 140 set at 28 inchs, add 2 extra head shims produces a solid 7800  rpm with 17x12
reg  blade APC. I see a lot of rpm ranges for this engine prop combo and anything in the 8000 and above I have found comes off
the pipe on long up lines.I was running 16X12 at 8600 rpm to pull 10.9 lb Focus around 2 years ago and this Greve set up produces
some serious pull on the 10.75 lb Focus I now have it on, a lot more torque and a lot quieter you have to try it to see it for yourselves oh fuel is 15% cool power. The engine does not seem to wind up high rpms but it seems to stay solid in the up lines.
enough for now. see yas at Muncie!       PS the rpm in higher at 7/8 throttle than at full, go figure?
Earl Vincent
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