[Mgs] Intermittent Fuel Starvation
Charley & Peggy Robinson
ccrobins at ktc.com
Mon Apr 24 05:27:18 MDT 2017
Every now and then the new viton tipped float needles are sticking on
one or the other of my HS-4 carbs. When it happens if I tap on the top
of the offending carb's float bowl using a screwdriver handle and with
the fuel pump energized, the needle valve opens and I can hear the fuel
pump fill the bowl. This started happening in the summer of 2016. I
replaced the needle & seat assemblies in both carbs with aftermarket
units. It didn't cure the problem.
Several weeks ago I put in new OEM viton-tipped needle & seat
assemblies. Then as I was adjusting the jets both carbs ran dry & the
engine stopped. So I tapped on one carb bowl & then the other, heard the
pump run while filling them up. The engine then started right back up.
Last time it happened I had the engine warming up, running at fast idle
when it started running very rough. I Tapped on the front carb bowl
whilst it was still running & it smoothed right out. Same thing happened
another time but it was the rear carb.
The fuel pump is a ~5 year old SU with points. I measured the fuel
pressure at the carbs to be 4 psi on the nose and it doesn't leak down
much or very fast. It has a new inline fuel filter mounted just before
the carbs. The floats are the all-plastic type and they don't show any
sign of leakage. The floats are very free on the swivel pins and will
drop to the stops.The swivel holes in the floats aren't visually
elongated and the swivel pins don't show appreciable wear. The carb's
vents are clear and I can blow air through the vent tubes.
I thought maybe the 7 month old gas might be a contributor to the
problem but we put about 100 miles on the car last Tuesday after putting
in fresh mid-grade gas, looking at Hill country wildflowers. The car
will maintain 70 mph in hilly country all day. Ran like a swiss watch
I'm at my wits end on this. Could pressure somehow be building up in the
bowls now and then? How?
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