1973 Chevrolet Van Either 307 305 Engine Would Cause Drop 18 Mpg 10 Mpg Had

1973 CHEVROLET VAN
10 MILES
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JAMESMK
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My van has either a 307 or a 305 engine. What would cause it to drop from 18 mpg to 10 mpg? Had carb rebuilt, new fuel pump, engine tune up.
Apr 7, 2013 at 4:13 PM
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