Holley secondary throttle plate adjustment

[Rob A.]

I've seen two different descriptions of the purpose of the adjustment screw for vacuum operated secondaries for Holleys. The first, is that the adjustment screw is to keep the throttle plates just far enough open to keep them from sticking to the bores. The second, and this is in Holley's own description, is that the secondary throttle plate adjustment screw be used along with the primary idle screw when adjusting idle speed. Which is correct?

[Gerard F.]

Re: Holley secondary throttle plate adjustment

I think it is your first. Adjust the secondary to full closed then 1/2 turn to to the open position. Then use the primary side for the idle adjustment.

Jerry Fuccillo

[Clem Z.]

on modified engines if you have to open the

primary idle transfer slot to more than .020 to get your idle speed up you need to also adjust the secondary to increase the idle. if you open the I.T.S more than .020 the idle/air mixture screws on the side of the metering body will have little or no effect because you are idling off of the I.T.S

[Mike G.]

Re: Holley secondary throttle plate adjustment

The Holley 2818's that I've owned have all required cracking open the secondary throttle plates a bit to lean out the idle mixture. The 4150/4160 book I have shows this method of dealing with a rich idle mixture.

You'll see quite a few Holleys with holes drilled in the primary plates for the same reason.