I recently acquired a 68 Plymouth with a stock 440. The previous owner blocked off the vacuum advance at the disturber and the carb. With this setup, the car starts right up and idles well, Though I do have quite a bit of hesitation during hard acceleration. When I hook up the vacuum, the car is hard to start, with less power, and with the same hesitation during hard acceleration. The high-speed cruise is smooth with both setups.

My question: What is the concept behind blocking off the vacuum advance? Should I keep the vacuum advance block? What might be the cause of the hesitation during hard acceleration?

 

Steve -

Welcome.

You can tweak a 440 to run with or without the vacuum advance.
I've run mine with and without, and except for a small timing adjustment, the difference isn't dramatic.
Basically, a mild 440 should like about 34* total advance, how it gets there usually only matters if you're racing.

Personally, if it wasn't done already, I'd start with a Mopar or aftermarket electronic ignition conversion.
Simple upgrade from points and the best $150 you'll ever spend on the car.

The hesitation, if I had to guess (which is what I am doing), would be in the carburetor, not the distributor.
A full rebuild might be in order, but things like float levels and accelerator pumps would be the first thing I'd look at.
But seriously, unless you have good documentation on the carb, rebuild it or have it rebuilt.

Archer

 

How much initial timing do you have now?
The vacuum advance being plugged probably will not have any effect on drivability more for cruz fuel economy.
I would try two or three degrees of advance and see if that doesn't help get rid of the stumble. The big block mopar with stock heads will like up too 38 degrees total timing depending upon your fuel quality.

 

Thank you guys for the information!