Tuning with Vacuum Gauge

[70_F100]

A tachometer is a better tool for tuning a carb, simply because you probably have a tach/dwell meter that you use for setting the points. If you don't, then you need to spend your money for one of them, instead of a vacuum gauge, because a feeler gauge isn't accurate enough to set the points right. Besides that, everybody has their own idea of how tight something should be against a feeler gauge. .001" is equivalent to about 2 degrees dwell, and the specs only allow .002" from min to max point gap. The only way to verify that they are set correctly is by checking the dwell.

Make sure the engine is at normal operating temperature, and with the air cleaner removed, set the idle speed to the correct RPM. Leave all vacuum hoses connected.

Slowly turn the mixture screws (ONE AT A TIME!) clockwise until the idle speed decreases. Then turn them counterclockwise until the speed decreases. Turn them back in until the idle speed is the highest. You may have to run them in and out a few times to get them right, turning them less and less each time. If the idle speed increases above specs, adjust the idle speed screw, then re-check your mixture again using the same process.

For emissions purposes, they used to say that after you got max RPM, turn them in (clockwise) an additional half-turn. That helped with the emissions and with fuel mileage. Certainly hurt the performance, though. That extra half-turn changed the air-to-fuel ratio from about 12:1 to about 14:1. Prior to 1968 (and the stricter emissions standards), the mix was always 12:1.

A vacuum gauge can be used for this, but basically what it does is the same thing as a tach. You're still dealing with RPM change. As idle speed increases, the vacuum will do the same. Same thing for decreased idle speed. Turn the screws in and out, like I described above, until you get max vacuum.

[JMcTurnan]

Yea, I already had bought a vacuum gauge. I used it, and I adjusted everything. To the highest vacuum, my timing light isn't that good I don't think. Because I used the vacuum gauge to time it, and it did better than the harbor freight timing light . But It purrs like a kitten now. It has been a long time since I have had a running engine. Thanks to everyone that has helped me. Before I had this truck, I knew almost jack squat. Now I can change starters, alternators, install crank kits, timing kits, carburetors, intake gaskets, and all that good stuff. What a learning expirience.