Put a timing light on the engine and see if the timing is changing in the idle-1500 rpm range. What happens is a person normally raises the rpm just before they start to let the clutch out. This may be causing the timing to change (advance) a lot. Then when the clutch engages the rpm comes down, the timing retards and you get a hesitation and a dead spot. I've cured this problem several times on stick cars. Ron
How did you go about fixing that? Stock distrib on this motor was 4 static, 11 centrifugal degrees, 15 degrees total advance! Vacuum added another 11. I hacked the distributor for +20 centrifugal degrees, running about 5 static.
It's a new distrib (well OK a year old now), a Pertronix Ignitor and epoxy coil. Distrib I recurved for a lot more advance. I did a how-to that's posted in the Technical Tips ("Hacking Delco distributors for more spark advance"), July 08. Still driving on that.
http://wps.com/AMC/1963-Rambler-American/Nash-195.6OHV-engine/Distributor/
