The electric pump will only turn the fuel starvation problem into a flooding problem, plus the mechanical pump might not draw fuel through the turned-off electric pump very well.
Most general-purpose vacuum gauges come with an assortment of fittings to adapt the gauge to various applications. I just use a short piece of rubber hose, attached to the inlet fitting of the fuel pump, or the fuel line at the tank outlet fitting, and plug the gauge hose onto that with the tapered adapter that comes with the gauge. A good-working pump at normal idle speed should supply a pint of fuel in 30 seconds to a catch can attached to the fuel inlet line of the carburetor. If there's fuel in the carb float bowl, it should idle for 30 seconds with the fuel line disconnected while you make the test. Just be VERY careful not to spill gas onto hot parts like the exhaust manifold. If the volume test is low, proceed with the pressure and vacuum checks.
Jerry
