Re: Terrible milage
I believe according to the Holley bible that your power valve rating should be half of what your idle manifold pressure is - so if your manifold vacuum of your engine at idle is 18 - then you would use a 9 power valve. My engine a 351 has a custom grind cam and idles at about 10 vacuum - so I run 4.5 rating power valve. You want your power valve to open only when you're under acceleration or pulling an load like going up a long hill. I have a in-dash vacuum gauge and to me is the key to see how your engine is running and a wise investment. I set the engine timing and carb idle mixture to achieve the highest reading possible. A reading of 21 is the very best you can ever hope for - I have achieved that by going down a big hill with your foot off the gas pedal causing your engine to act as a compressor.
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