The best way to determine the optimum jet diameter is on a chassis dynamometer.  Since this can be quite expensive due to the time required to remove & replace the carburetor while changing primary jets, I opted for the much cheaper time-trial method.  This involved multiple timed runs from 0-60 mph.  While a drag strip would have been better, I found a nearby straight length of road with very light traffic and got my wife to take several measurements with a stopwatch for each jet..  To keep the times as consistent as possible, I left the transmission in Drive where it shifted from 1-2 around 4500 RPM.

Sticking with the 52 metering rod, I have the following results for a variety of main jets:

Main Jet Average 0-60 times 1,2
seconds
77 not tested
76 not tested
75 15.2
74 15.2
73 14.7
72 15.6

Notes:

  1. APT adjustment @ 3.5 turns, Secondaries locked out, transmission automatically shifting @ ~4500 RPM
  2. 0-60 times reflect that this car has highway gears (2.76:1) and larger tires (P225/70R14) than stock (P185/75R-14)

Besides having the quickest 0-60 time, the #73 jet also had the best seat of the pants feel.

Custom Search