Classic/Antique Car Repair: Chevy 235ci hesitation, propane torch, vacuum leak

Question
I have a 1954 Chevy 1/2 ton with a 235 six engine. It was rebuilt 20,000 miles ago. The engine has good compression 140 psi, but only 15 inches of vacuum at idle. This causes a hesitation on acceleration. I must drive with the manual choke pulled out a little. I can't find any external manifold leaks. Could I have a vacuum leak internally in the intake/exhaust manifold. Thank You. John

Answer
The answer is yes there could be a leak between the intake and exhaust manifolds. The easiest way to find it is to remove the carburetor and look down into the bore. However make sure that the points are properly adjusted and that the timing is set correctly. closes down and the timing is then retarded because the points open later on the rubbing block. I use a modified propane torch when checking for a vacuum leak. I remove the burner and the metering orifice. Add about two feet of flex fuel line to the torch and turn on the gas. With the engine running probe all of the places that might leak vacuum. When you discover a leak the engine speed will change due to the gas being drawn in.
Brad