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PS 5C pressure carb

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Feb 5, 2014
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Hoping someone with knowledge on the PS 5C pressure carbs can help out please.

I have a Pitts S-1 with an O-320 and pressure carb which I have repaired and is almost ready to flight test. I bought the aircraft damaged so have never flown this particular one. In all my twenty something years of aircraft maintenance I have never worked on a pressure carb, so this is new to me.

Doing some ground runs on the weekend, it seemed to be starting easily and running well and making full power while I ran a dynamic prop balance and was making minor idle speed and mixture adjustments when suddenly it wouldn’t start.
It had fuel pressure available at the inlet hose fitting but would not prime.
I could only get to about 5 psi on the boost pump but I could hear the fuel returning to the tank through the return line.

In case it is a clue, I did notice when running it that fuel pressure was at times getting up to a little over 20 psi although it was running well.

Reading the Pressure carb manual has not given me any ideas other than it could be a problem at the poppet valve and it’s not regulating the pressure but dumping it all back through the return line.


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