If the secondaries aren't setup correctly, will that affect the mixture screws? Right now, to get the engine to idle its best, the screws have to be in different positions. I was in PepBoys and I was looking at a Holley manual and it said to "open" the secondary set screw to adjust the secondaries to get it to idle off of the mixture screws better. Can somebody elaboarate on this for me please. Carb is a 750DP.

Vince......Its just a matter of cracking the secondary blades a tad so we know for sure the secondary idle circuit is activated.....this is only true if its a 4 corner idle circuit carb.....just make sure they are cracked a tad and that will help....There is a screw coming in from the bottom of the base that hits that lever on the passanger side of the secondary throttle shaft.....or you can just put a tweak on the lever so it hits the screw sooner......good luck! Jesse @ BIGS!!

cracking open the secondarys blade is a trick for the engines with a big cam and you have to open the primaries to much and uncover the idle slots. you can also drill the primary butterflys which also lets in more air just as cracking the secndaries open a little more does. but drilling is more of a permanent fix and you might want to study up a little more before doing it
what cam are you running and how much vaccum at idle do you have? also timing has a big affect on the idle quality, the bigger the cam the more intial timing you need.

I adjusted when the carb was off - i backed the screw out, then screwed it in till it just touched the lever. I then gave it a 1/4 turn. The motor is a 454ho stock, so it really isn't radical at all.

All Holley 4 barrels have a secondary idle circuit. Even if the secondary circuit isn't adjustable. This is to insure the fuel doesn't go stale in carbs that never have the secondaries opened, not usually an issue with anybody on this board smile.gif . It's a good idea to have the secondaries cracked open a bit on any Holley.

How much is a bit?

Here's another question. If the secondaries are set correctly, should the engine die when you back-out the idle screw, or should it be able to idle off of the secondaries?

Anybody :(

Vince.........the engine will not idle only off the secondarys usally......especially if its a non-4 corner idle circuit carb(aka, air mixtures screws in secondary block also)....just the "constant feed" thats drilled in the base of a non 4 corner idle circuit carb is not really an idle circuit, just a fuel adder threw roughly a .025 hole..........Jesse

Thanks Jesse!