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1. 03:42 PM - needle valve (Bobby Paulk)
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All,
I have a Jab 3300 that has never run right since new. It was flooding at
idle and blowing soot out the exhaust. I had to clean the plugs several
times in 25 hrs. I decided to run a bench test on the needle and seat. I
filled a Tupperware type clear bowl with fuel and sat it on the bench. I
removed the Carb from the A/C and removed the Bale from the float chamber on
the bottom of the Carb. I connected the fuel line to a regulated air supply
of 5 psi with a calibrated 0 - 5 psi gauge only inches from the carb fuel
inlet. I sat the carb in the bowl of fuel so that the top of the fuel would
be even with the split where the bale was removed. I got a friend to
increase the pressure slowly while looking for and listening for bubbles.
The carb started passing gas (pun intended ) at 1.5 psi. I repeated the
experimented with this by raising and lowering the carb out of the fuel and
back in. the results were that the needle was not seating at a very low
pressure.
I decided to polish the needle seat with a rounded wooden dowel and fine
valve grinding compound. With light finger pressure I began turning the
dowel and discovered a burr on the seat caused by the drill bit or tool used
to drill the hole. I used a larger drill bit with very light finger pressure
and turned it on the seat. I saw shiny metal around about 40% of the seat
where the burr had been removed. I finished polishing the seat and the
needle would hold bubble tight to over 4.5 psi.
If you are having problems with the engine running very rich at idle you may
want to see if the needle valve seat is smooth.
Bobby Paulk
Zodiac 601 XL
N131BP
55 Plus hrs.
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