Carb troubleshooting

[wtm442]

Sounds like you are a lot better off than last week.

Holley supplies carbs where the secondaries could be the same size as the primary jets, and some with as much as 10 jet size difference. The best way to size jets is to put it on a dyno. Then the air/fuel ratio will tell you what to change. Then when you are in the ballpark and the A/F ratio is correct per the dyno, go up 2 sizes on the primaries and see if the car feels better. If not, go back to the size you had. Then try it on the secondaries ... go up 2 sizes and see if the "feel in the pants" is better.

I've got a 750 CFM Holley, and right now I have the secondary jets 6 steps up from the primary size. My carb runs best with idle screws about 3/4 of a turn off the closed seat.

I am a little confused by your last paragraph. The accelerator pump spring should be adjusted (with the carb at idle position) until there is clearance. Then relax the spring until it hits the arm and there is no clearance. This makes sure that you get gas thru the squirter as soon as you step on the gas pedal. Then open the butterflies to WOT and check to make sure that there is at least 0.010 clearance (ie additional stroke) by pressing on the pump lever in the center of the diaphragm. This is to insure that you do not "bottom out the pump" at WOT.

As far as the best position for the idle screws, I use a vacuum gauge to get the best vacuum at idle, and then drive it to see if its OK. Many times a slight adjustment is required after setting by the vacuum gauge.

I've never heard of the "tap the acc pump" method for adjusting the idle screws. But if it drives OK, don't worry about it.

Might be a good idea to change the spark plugs.