Holley 5200 idle jetting mystery

[Anonymous]

I've been tinkering with my jets on the Holley 5200 I installed on my '62 Falcon since I bought it from Stovebolt a couple of months ago. I finally have the primary and secondary mains and air correctors zero'd in, but my main idle jet doesn't seem to behave the way the manual says it should.

The manual (and here in the forums) the procedure says you'll basically have the correct primary idle jet when the idle mixture screw sits about 1.5 turns out.

Not mine.

I started with a size 65 jet and I had to turn it four turns out. A 70 brought it it 3.5 turns out. A 75 made it three turns out. Seeing a patten? Now I have an 80 in there (the largest size I can find) and I'm about 2.67 turns out. The graph in my head thinks this shows that I would need a 90 or 95 idle jet, which I doubt exists.

Two questions:
(1) Why is this?
(2) Should I care? The car runs fine. But I think I can get better in-town mileage.

My engine is a 200ci with Pacemaker headers, a C4 transmission (that sucks), and a DUI distributor.

The rest of my jets are as follows:
pri main - 150
sec main - 155
pri air - 180
sec air - 190
pri idle - 80
sec idle - 70

 

[cfmustang]

Vacuum leak?

If you are running too lean because of a vacuum leak, that would cause you to have to richen up the mixture to compensate.

The other thing I can think of is that your idle is set too high so the throttle plate is exposing the main slot in the carb. That causes your mixture screws to be less responsive, I believe...

 

[Anonymous]

Hmm.

I only have two vacuum lines and they seem to be alright: I have on from the intake to the tranmission, and another to the PCV valve. I would like to point out that I've never liked the way the PCV just sits on top of the valve cover. It isn't tight at all. I've often wondered how tight that PCV valve needs to be because it seems like a big, fat vacuum leak to me.

When I get home I'll disconnect both lines and see if the carb behaves any differently.

Also, the idle isn't very fast at all, so I doubt that its a problem with just a high idle setting.