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Discussion Starter #1
Ive been ironing out (over the span of time) the holley 600 on top of my hungry Cleveland......today I decided, since this holley is a plain jane 600VS, I'd drill the primary throttle blades with a .050 bit so I could turn out the idle speed screw and stay out of the transition and ported vacuum.

At the same time, I made sure the secondary idle speed screw underneath was turned as far as possible without uncovering the transfer slots.....worked like a charm; I have a good idle rpm with no ported vacuum, and she even idles slightly smoother (I have 64 primary jets right now...which upon a time used to be a little rich; I have a feeling it's the gas these days).


I also considered another tuning concept. If the idle speed is high enough the ported vacuum is applied, the mains are being used somewhat.....if the main mix was off, idle quality would be affected the same as if the idle mix was off when the idle speed screw isnt so far out.

This might be a helpful tuning idea.....bearing in mind even on very well tuned carbs and engine combos sometimes the transition area isnt perfect and how the engine acts under load is a horse of another color.



Anyways, I thought I'd post these two concepts up for anyone interested.
 

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I don't know how much vacuum you have but I suspect it's not much. One trick I read is to use manifold vacuum to a vacuum advance distributer. Most Ford cans are adjustable, you might be able to get it to pull timing in at your vacuum level. The extra timing will help idle quality, hopefully.

I understand that a lot of engine builders who build low compression engines with huge cams do this in an effort to build up the low end torque.
 

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Discussion Starter #3
I have 12" at idle....


Just got back from test driving.......ran fantastic!!!


BTW...thanks for the suggestion!!!
 

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Beginning with the April 2001, I believe, production Barry Grant has a .030 hole drilled in the carb base plate at the juncture of the 4 venturis, The hole is inset into a recess, like a counterbore, that has an "X" milled in it. This is supposed to be the equivalent of drilling a hole in the throttle blades, plus the "X" slots balance the effect among the 4 venturis. As luck would have it I purhcased my speed demon carb just before they made this manufacturing change, although it appears in the instructions. Glad to read that your carb is tuned right for you. Once the carb gets dialed in it sure feels good to drive with the engine at its "sweet spot".
 
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