IML: '72 Surging at highway speeds

[Joe Strickland <jwstrick426@xxxxxxxxxxxx>]

While checking for vacuum problems with the distributor, also check the choke pull-off diaphragm located on the carburetor.  The diaphragm on these can crack open and cause rough idle plus other symptoms while driving.  Since the cars are the age they are now, rubber parts like the diaphragms on this and the distributor can easily be a cause of driving problems.

One item often overlooked on distributors involving timing advance is the spring controlled centrifugal advance.  This consists of two weights that have a pivot point and a pin that a spring connects to.  The spring causes the centrifugal arms to return to the idle position as the engine RPM slows down.  They are located under the star wheel and the steel plate just under it.  The factory lubricated these with some grease that dries out with time and exposure to heat etc.  These can cause some tricky problems that change as the engine warms up.  Sometimes pinging will be experienced under moderate acceleration, but not under full acceleration etc.  Cleaning and re-lubrication will correct problems there.

Joseph W. Strickland
1021 Vaughan Lane
Tioga, TX 76271-2937

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