Originally posted by 71Demon
Denny above said check your power valve. A back fire usally blows them, if they don't have the protectors. If the idle air screws (actually fuel screws) don't shut the engine off when you run them in all the way in, then it is blown. That is the easiest check for a bad power valve.

Now to set them correctly take them out to between 1 and 1.5 turns from home. This is where the should be. As you run them in and out, the rpms should rise and fall as you go rich and lean. You want them set where the rpms peak, and that should be between 1 to 1.5 turns. If it is not, and you can shut the engine off by running them all the way in and stopping the fuel flow, then you have a working power valve, but on that is the wrong size.

If the peak is under 1.0 turn, then the power valve is too large, if it is greater than 1.5 turns then the power valve is two small.



You don't need to drill holes in the throttle plates. There is an adjustment for that. It is not easy to do buy it is there, and you don't have to buy new throttle plates if you drill holes two big.

If you look at the underside of the carb, you will see two slots in the bores for the primary, at idle you should have 0.020 of an inch of those slots exposed for the idle air circuts to operate correctly.

If the engine doesn't have enough air to idle at that setting, then don't drill holes in the primary plates use the adjustment. If you look at the underside on the secondaries, you will see an adjustment screw. That screw is for adjusting the air flow on the secondaries at idle. That is so you can get the front set with the .020 exposed, and still get the right airflow for idle.

Hopefully that will help you get it tuned in a little better.

Gary
I got the carb rebuilt, its still running rich. the only way i can lean it out is if i turn the fuel screws 1/4 turn from fully shut. are you saying that this indicates that i need a new power valve? i

Thanks