Ted.  I've been having trouble eliminating a hesitation off idle with a 600 Holley on my 312. Put a 390 Holley on it and it runs good now but without the performance that I would like. I was going to buy a 500 Edelbrock for something in between but from what i read the Summit 750 should work for me?  Dave V

SE Wis

Try jetting up two sizes on the primaries only, that works more often than not.

-Gary Burnette-

Thanks for the reply Gary.  Now I'm confused. Doesn't coming off idle have more to do with the accelerator pump and discharge nozzles?  Dave V

SE Wis

Hesitation issues are typically a result of a lean condition which can be fixed from several different approaches.  Gary is correct in that richening up the primary jetting can help with hesitation issues.  A larger accelerator pump shooter and/or pump cam can also help.  Reducing the idle feed air restriction holes is another option.  Balancing the primary and secondary throttle blades so that the transition slot in the primary side is not overly exposed is also another fix.  I’ve gone so far as to change out the fuel discharge nozzles to a different design on some carbs in which to increase the booster signal at low rpms.

Lorena, Texas (South of Waco)

While I was playing with the accelerator pump on my 570, I noticed that some of the cams would not operate the pump arm immediately, I think in position 1.  That can cause hesitation.  Make sure the accelerator pump is operating correctly.



Lawrenceville, GA

Thanks for the replies and ideas. Hopefully I'll have a chance to try some before we get snow and salt on the roads.  Thanks again.  Dave V

SE Wis