On 11/26/2015 05:49 PM, Micky wrote:
I'm not sure it has any. It has something called a control valve,
with gas in and out and a vacuum line from the base of the carburetor.
??

I forget to turn it on I can get about 100 yards before the float bowl
runs dry. Vacuum actuated petcocks can act up too or the vacuum line
Is that what the control valve is?


Sounds like a vacuum operated petcock. A potential problem with gravity
feed fuel systems is a leaking float needle in the carburetor itself or
a stuck float. The float bowl fills and the gasoline starts to run out
of the carb. Worst case, it fills the cylinder and/or crankcase with
gasoline.

Traditionally there was just a manually operated valve on the bottom of
the tank, with on, off, and maybe reserve. Reserve just uncovered a
lower hole in the tube inside the tank. When you started sputtering in
the normal position you switched to reserve and might get a half gallon
or so additional fuel. Of course, if you reached down and found you were
already on reserve you started walking.

Like everything else, that was too complicated for people, so they went
to a vacuum operated valve, with a hose going to the carb for the
vacuum. Those generally still have a three way lever, on, off, and
prime. Prime manually opens the valve in case there's a problem with the
vacuum operator.