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Old 09-29-2011, 01:04 PM
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Quote:
Originally Posted by nanmer
Ok.i purchased a oiled filled gauge. It reads 7 psi. A little confused. Some say 5-7 psi is good readings for a mechanical pump while others say 5 psi only.
It's just natural for hot rodders to think that more is better because it's true in many aspects of car building. In the case of a carburetor, it is not the truth. Your motor will operate better at 5 psi max using a Quadrajet, Carter or Edelbrock carb. Holley's will tolerate another 1 psi, for a max of 6.

More pressure will not make more horsepower. It will over-ride the needle and seat and blow raw fuel into the intake manifold, creating a tuning nightmare.

Find a way to drop the pressure to 5 psi at the carb inlet and you will be rewarded with a system that functions properly. If I had a mechanical fuel pump and it was delivering 7 psi, I would either replace it with a pump that delivers the proper pressure or I would rig up a bleed back to the tank, with an adjustable screw to limit or allow more fuel to be returned to the tank.

The Carter muscle car mechanical pumps spec a little higher than 5, but seem to work well on a street application....
http://www.summitracing.com/parts/CRT-M6624/
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