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Holley Idle 2 schools of thought

699 Views 15 Replies 5 Participants Last post by  PRNDL
So which school of thought do you guys recommend as far as idle is concerned?

Secondaries closed with just a small 1/8 turn to prevent binding. Then set the idle via the primaries only?

or…

Secondaries adjusted to match the exact same level as the primaries. Then make idle adjustments by adjust both fronts and rears the exact same?

Both methods assume the primary transitiin

AED Holley 750 HOHP DP 4 corner idle. Came with 1/8 holes in primaries only. and PCV hooked up. One inch open spacer.

The engine is a freshly rebuilt 383 stroker. All machined, brand new stroker internals, 30 over, zero deck, 6 inch rod Skip White unit with 10cc dished pistons. AFR 195 heads, Performer RPM AIR GAP, dual plane, and Comp Cams XR282HR 230/[email protected] 110LSA CAM. HeadersBreak in has been completed.


I’m noticing that if I set my idle to 900 rpm via the first method, primary adjustment only, my rear idle mixture screws stop responding. I can screw them in all the way and no change.
When I set the idle via the second method, primary and secondary matching, to 900 rpm, the front mixture screws stop responding.

I’m thinking of lowering my idle to 800 rpm.

Any ideas?
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Discussion Starter · #5 ·
Thanks Eric, I was going to ask this on the other post, but I thought the question was too specific so I thought it would be more proper to keep it simple and start a new thread. On the other post, my timing resolved my issues of running rich at idle. I bumped the initial timing much higher. This seems to be a final fine tuning issue.

My secondary transfer slots sit much higher in the barrels.

Not sure why AED drilled the primaries, but it’s a standard mod with this HOHP 750. I spoke to the owner of AED and he said not to touch the secondaries. They explained that the drilled primaries mean no cracking of the secondaries at idle. Problem is my idle would be too low. My engine seems to prefer the secondaries matching the primaries method. Problem is I lose control of the primary mixture screws. When I close the secondaries, I lose control of the secondary mixture screws.

by losing control, I mean, when I close them, the engine does not stall. Should the engine stall when closing any one of the 4 mixture screws? I guess that is my true question.
 

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Discussion Starter · #7 ·
Thanks guys. The one inch spacer is for clearance issues. I’ll look into a 4 hole.

so with the primaries set and the secondaries opened to match the primaries, if my idle is too high… Do I adjust them both down or just the secondaries
 

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Discussion Starter · #9 ·
Thanks brother. Great info. I set it how you said, ignored what AED said and my idle mixture screws work well. I reduced the idle to 900 by turning both primary and secondary idles down a hair. It’s idling very happy. It absolutely does NOT like the secondaries closed at all.

So here are my stats…
Primaries T-slot at .030. Primary idle screw at 3/4 turn. Secondary idle screw at 3/4 turn. Idle at 900 in park. About 850 in drive.

weird part. Front idle mixture screws want to be at 1-1/4 and the rears at 1 turn for 11hg of vacuum and best idle. I used a vacuum guage and remote tach under the hood. Lastly, all mixture screws respond well, but I can close the rears and no stall. Only the primaries stall the engine if closed.

What are your thoughts on the mixture screws?
 

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Discussion Starter · #12 ·
That’s great info Eric. You know, I read somewhere a while ago, where a few guys turn the rears out just 1/2 and do all the idle tuning with just the fronts.
 

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Discussion Starter · #14 ·
That’s my next move this weekend bogie. While trying to fine tune, I learned the following….

If I set it the traditional way with the secondaries closed, my primaries need to be opened way too far. This renders my primary idle mixture screws dead and my secondary mixture screws hyper sensitive.

If I set the primaries to .030 T-slot exposure with the secondaries open to match the primaries, the engine is way happier. The front mixture screws come to life and become very sensitive. However, the rear ones go kind of numb. They allow for adjustment, confirmed via vacuum gauge, but if I close them, the engine keeps running.

Through experimenting, it seems this engine carb combo wants a hybrid of both methods. Seems opening the primarily plates an 1/8 of a turn, showing .035-.040 T-slot, and closing the secondaries and 1/8 evens out the sensitivity of all four mixture screws.

So instead of my primary curb idle being at 3/4 turn and secondary curb idle being at 3/4 turn, I’m now at 1 turn primary and 1/2 secondary.
 
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