Time out.......... ???

What vacuum ports on the carb?  I am pretty sure the VM carbs don't have vacuum ports.  The only vacuum port you would have with a VM carb would be if you installed a new manifold with one to drive the petcock.

Can you show a picture of the ports?  or describe them in detail where they are?

Don't they have synchronizer ports???

Those are vacuum.

there's a port on there on the one I got from Lancer.  it goes through the throttle body on the engine side of the carb.  I had it hooked up to the vacuum port on the petcock for the same reason as Rob.  Will take a pic as time permits.

V

I agree it is a vacuum port although not stock for a standard replacement VM36 carb.  It has either been added or it is a non standard carb from some other application.  Either way it will provide vacuum for the petcock.  however if you are having idle problems (different from your overflow) it could be a vacuum leak causing a lean condition at idle.  This could be either the vacuum hose being cracked, the vacuum port leaking where it goes into the carb body, or the rubber intake boot on the engine being cracked or leaking where it mounts to the engine.  .... or it could be something other than a leak.  Normally if it is an air leak it will run better on just a little bit of choke....that is a sure sign of a lean condition.

you said it overflowed gas but the valve needle shut off.  Did you shake the float to listen for gas in it?  (first question is it the old brass style?)  I had one on my old GT spring a leak and sink a float.  valve worked fine but the float wouldn't float!!