Classic/Antique Car Repair: 1963 Studebaker Avanti R1, loss of power on acceleration with a load

Question
On the above car we have changed the plug wires and plugs and set the points.  The Avanti starts, revs up and idles perfectly.  But when you take it on the road, and shift from 1st to 2nd and 3rd and 4th, it misses on acceleration.  It was running really good a couple months ago.  It's a 4-speed, 289 Studebaker original motor.  What might you think I should check next?

Answer
A true miss on acceleration, one that you can feel each cylinder not fire, is caused by either a spark plug or two not firing or a valve not closing tight. In the spark plug theory the problem could be a cracked or defective plug, a bad wire, a cracked distributor cap or rotor, or a defect in the ignition coil. If a valve it could be a sticking valve in the guide, that is eating tight enough when the engine is under light load but when pushed does not seal tight. I would take a compression test on the engine as my first step. All cylinders should test within 25% or each other. Then visually check the ignition items that I mentioned. Also make sure that there is no play in the distributor shaft and that the points are set on the money. I assume that the distributor that you are using has the dual point set up. If so then there are two different specs depending on what ignition point set you are using. One has a 1 inch long point arm and the specification for that is .019" while the 1 1/4 inch long arm is .017". Remember that when setting the points if one set of point is on the high spot of the cam the other set is offset slightly and will not be on the high spot so you will need to turn the shaft slightly.