Motorcycle Repair: 78 cb550k stalls when the gas is turned on, overflow tube, needle spring

Question
the engine runs great with the bowls filled and no continuous fuel being fed. As soon as the carbs are hooked to a gas tank any known working tank, and the petcock is opened all 4 cylinders start to die & stall. Close the petcock and about 10 seconds later all 4 cylinders start purring again. Carbs have been cleaned, floats adjusted, New slow jets, New idle screw O-rings,

Answer
Hi Dale,


Only a few things can cause the carbs to
overfill or flood the engine with fuel.

1. Faulty floats, the composite material can absorb fuel
through cracks or by just being generally faulty.
This causes the floats to sink in the fuel
instead of floating and shutting the fuel off
at the correct time.

2. Float needle/valves leaking or loose.
The float needle/valve seats may have an o-ring
under them. If you did not replace these
then all four carbs could leak around the
needle/valve seats inside the carbs.

3. Carb body air vents plugged or incorrect hose routing.

4. Cracked brass float bowl overflow tube(s)

5. Floats adjusted too high, not shutting the
fuel off soon enough. Sticky floats.

Floats have to be set so the float level
is correct (22mm) with the float needle just
touching the float's tang, the needle
spring cannot be compressed but the needle
should be just barely closed while adjusting.
The float level is the distance from the carb body
to the float's bottom side.

Good luck!
Wayne S.
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