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From Another Forum:

The ECM is no longer in my '81 so how much does it impact my MPG? I swapped out my electronic '81 carb for an '80. I am only getting about 110 miles on 14.5 gallons so a little over 7.5 mpg. If the ECM does not play much of a factor in fuel mileage how can I improve my fuel mileage?


The '81 distributors don't have a vacuum advance nor any mechanical advance mechanism so this forum member's '81 only has its initial advance of 6 degrees. With only the 6 degree advance his engine will run HOT at anything above an idle because the flames will be chasing the pistons down during the power strokes. He needs a '74 through '79 HEI distributor with a vacuum advance.

Remember, all combustion takes place before the pistons reach TDC and that's why engines need around 50 to 52 degrees of advance at light throttle cruising speeds.
 
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