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Old 10-16-2012, 02:08 PM
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Originally Posted by mustang 671 View Post

high volume engine run fuel pump

weiand 6/71 blower with 2x holley 600 vac secs carbs

it will not idle and i have to keep the revs high ( say 1500 to 1800 ) but it is still rough at that rpm

do you have any idea on if my jets are too big ? it doesnt change when i adjust the air mix screws . they are currently out 1 turn .
The first thing you'll want to do is to get the fuel pressure under control. Some fellows forget this all together and other fellows think it doesn't matter. Carburetors are not like fuel injection. More pressure will not make more horsepower. The filling of the fuel bowl is controlled by a needle and seat arrangement that is sensitive to pressure and although Holley carbs can stand just a little more pressure than, for instance, the Carter AFB/Edelbrock design, you can still introduce only about 6 1/2 psi MAXIMUM PRESSURE into the carb inlet before you overpower the needle and seat and blow raw fuel into the intake manifold. I generally recommend a maximum of 5 psi just to be on the safe side. With carburetors, you need to concentrate on high volume, not high pressure.

What you'll want to do is to tee off at either of the carb inlets and run a small copper line back to the firewall, then up past the hood lip and to the cowl. On the cowl, temporarily mount a mechanical 0-15 psi liquid-filled fuel pressure gauge so that you can monitor the pressure going into the carbs by reading the gauge through the windshield as you drive. The better the quality of the gauge, the better the resolution you will get from it. The mounting system for the gauge won't have to be fancy unless you intend to make it permanent. You can make do with duct tape and tie wraps just for getting the pressure under control, then removing the line and gauge. Personally, I would want to keep it there permanently, but that's just me.
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