FYI FORD MustangSteve's Ford Mustang Forum / Need to rejet the new Holley

**Posted by MS** 9/02/2024 7:39 PM

670 vac secondary on my 66 427.
A/F ratio gauge sits at 12.8 at steady 60 mph. Around 11.0 at full throttle second gear.

I’m thinking about two jets sizes smaller in the primaries should get it close.

Whaddaya think? I figured the collective experience of this group might help me dial it in with fewer jet changes. Will address the secondaries after the primaries are closer to right. It is going to be hard to beat the way it runs right now.

**Posted by rpm** 9/02/2024 9:52 PM

For being that far off I'd jump four jet sizes on primaries, and two on secondaries.

**Posted by Cab4word67** 9/02/2024 10:45 PM

Well from what I remimber about carbs is if you go to lean in the primaries it will surg at part throotle then go up one size after you get rid of the surg.

**Posted by TKOPerformance** 9/03/2024 6:28 AM

We always used to tune by going up or down at least 2 jet sizes at a time. A single step up or down was for fine tuning once we were close. But since you actually know the A/F ratio and its pretty far off I'd agree with rpm and drop down 4 and 2. I'd want to see near stocih at cruise and 12:1-12.5:1 at peak torque.

I'm guessing you're running 32-34 degrees total timing?

**Posted by MS** 9/03/2024 8:31 AM

Thanks, guys. Will let you know how it turns out.

**Posted by rpm** 9/03/2024 10:27 AM

What are your idle numbers?

**Posted by MS** 9/03/2024 1:05 PM

rpm wrote:
What are your idle numbers?

13-14

**Posted by rpm** 9/03/2024 2:06 PM

MS wrote:
rpm wrote:
What are your idle numbers?
13-14

👍

**Posted by Steve69** 9/03/2024 5:44 PM

When I called Summit Racing they also said two jet sizes. I was adjusting my idle mixture screws yesterday and I can get them perfect near 14.7. Then drive the car again and there to lean. Seems like they’ll never be consistent.

**Posted by MS** 9/03/2024 8:27 PM

Went with two sizes down. It now has 66 primaries./77 secondaries Running ar 2,000 rpm (while parked) it is at 13.8, so maybe another two will get it there. I was able to get the idle near perfect.

Will test on the road tomorrow. It was raining (!!!) tonight when I got it back together. I am not sure how being under load will affect the A/F ratio vs sitting still.