when I check my timing I pull the vac advance hose that goes to the dizzy off the carb port. I cap the port on the carb and stick a screw driver in the line going to the dizzy. then set the timing base.
you want to make sure that when you hook your advance hose to the carb that you hook it to the timed vac port (only pulls vac above certain rpm) ....not the manifold vac port (pulls vac immediately at idle even which can cause the dizzy to advance at idle and advance to quickly/to much to soon when giving it gas).
