I am currently working on my brother's 83 Dodge van (again). The van is currently equipped with a NOS Holley 2280. 1976 short block bored .060 over, stock 1983 hydraulic cam, 1972 198 head with Ford 300 valves installed. The 2280 is of the variety that has no mechanical power valve, only the vacuum operated power valve.

The van was getting worse than usual fuel economy (yes, I know I shouldn't expect more than 12-15 MPG with a van) and the exhaust was very smelly. While I was looking the engine over, I discovered that one of the rubber caps on the vacuum tree on the #6 intake runner had cracked, creating a vacuum leak. The motor still developed 21 inches of vacuum at idle, but this cracked cap definitely was creating a vacuum leak.

I replaced the cap and the motor runs ever better now. Vacuum is up to around 22-23 inches at idle. The exhaust isn't as stinky too.

I have a question about the vacuum power valve and vacuum leaks. Would a vacuum leak cause the power valve to richen the fuel mixture too much? I am assuming that the vacuum operated power valve increases fuel flow as manifold vacuum decreases. Would a vacuum leak cause an artificially low manifold vacuum signal leading to the carb running rich?

The plugs looks fairly clean and tan, so the motor was not running excessively rich. Am I hoping for too much to hope for some improved MPGs?

Thanks!

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Casually looking for a Clifford hyperpak intake for cheap.

Your theories and guesses/hopes are correct right across the board -- a vacuum leak will indeed make the power valve open "early" and stay open "late", dumping in a bunch of extra fuel.

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Too many people who were born on third base actually believe they've hit a triple.

Cool beans. I can't wait to get it all back together and see how it performs.

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Casually looking for a Clifford hyperpak intake for cheap.