Holley 4160 Air Bleed and IFR tuning with O2 gauge. Help needed

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robertodonnell

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Hi everyone,

I have a mildly tuned 318 in my '65 Valiant, and I'm wanting to dial in my AFR in the light cruise area better. Carb is a standard 600 vac secondary Holley list 80457.

At this stage, the car is running very well, auto choke working properly and the car runs without any bog or lean/rich stumbling. Mash the pedal and she runs smoothly to redline from any gear (T5 manual). But, it runs rich (12.5 - 13) in light cruise.

I know that the main jets don't come on until well after 2000 RPM, and as I run a final drive where I'm turning about 2000 revs at 65 MPH, I need to tune the idle/transition circuit to get in the mid 14's. Today I tried some wire in the Idle Feed Restrictors, but all this did was serve to make my idle so lean that I needed to back out the mixture screws to get my idle back in the mid 13's where it idles best, and then my light cruise was back in the 12.5 to 13 range again.

If I lean my idle to a nearly impossible 16:1, I get my light cruise in the low to mid 14's. The car is undriveable off idle, and naturally is a pig at the lights.

So, how do I get my idle AFR in the mid 13's, and my light cruise in the mid 14's? I am thinking it's time to work on the Air Bleeds, but I'm not sure.

I've been reading the Yellowbullet Forums, and the Burton Machine tuning sheet, amongst all the other Google results, but I am hoping someone on here has done similar and can suggest a path forward.

I've also been on the Holley forums, but there is very little activity there, and lots of threads with 0 replies.

I have a spare 4160 that I can work on, so drilling the bleeds isn't the end if I stuff up.

Thanks is advance guys, cheers.

Robert
 
This is a situation where slightly increasing the sizes of all four idle air bleeds might work (even the 2-corner Holleys have them on the secondary side). Unfortunately, on that carburetor, they're pressed in. Of course, in your case, you could drill them one-thousandths at a time until you're satisfied, but there's no going back when you get the drill out. Some people will drill and tap the air bleeds for small drilled screws for adjustability, but it might be that you'll want to leave it alone if the highway cruise AFR is acceptable. I've done wideband tuning on all 6 of my cars. The '60s cars that still have factory jetting cruise in the 13-13.5:1 AFR range when they are on the idle circuit. When I have a car that runs in the 14-15:1 range at low speeds, it often hesitates, surges, or does something untoward in some way.

***EDIT: Is the car running 12.5:1-13:1 at 65 mph? If so, I would open up the air bleeds a thousandth at a time. I wouldn't lean it out past 14:1. I thought it was running that AFR in the 30-45 mph range. What's the AFR when the mains come on?***

Some people are wizards at making their carbs transition from a 16.5:1 cruise to a 12.5:1 power AFR with no hiccups and they claim to get 40 MPG in the process and run 11s. I am not one of those people. My goal when tuning a carb is to highway cruise at 14-14.5:1, run full power in the 12-13:1 range, and light cruise on the idle circuit at 13-14:1. Granted, my mileage on these things isn't always spectacular; however, I rarely drive them on the freeway all day, and their driveability is acceptable to me.

Good luck!
 
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here's a portion of a good article on the 3310 750 vac secondary and applies to your 600. Page 50 of the Hot Rod article addresses your rich cruise and drilling the primary idle bleeds larger to dial in a leaner cruise AFR. I would leave the rear idle bleeds alone since they are very small and are mostly there to allow a small amount of rear idle fuel to flow to keep fresh fuel in the rear bowl when the car is driven without secondaries coming open.
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Thanks guys,

I've read the Burton machine article many times, as referred to in my original post. It's what got me motivated to do this.

The car runs about 13 in the 40 mph range, and the mains don't come on until after 2000, so I assume my 65 mph is about the same. When the mains do come on, the AFT actually goes up to the low 14's!

What I really want to know, is whether opening up the low speed bleeds will not just lean up the light cruise, but also lean up the idle, which I'll just have to chase with the mixture screws, and be back where I started.

By the way, this forum is awesome! Can't say the same for the Holley one...

Cheers,

Robert
 
robertodonnell said:
Thanks guys,

I've read the Burton machine article many times, as referred to in my original post. It's what got me motivated to do this.

The car runs about 13 in the 40 mph range, and the mains don't come on until after 2000, so I assume my 65 mph is about the same. When the mains do come on, the AFT actually goes up to the low 14's!

What I really want to know, is whether opening up the low speed bleeds will not just lean up the light cruise, but also lean up the idle, which I'll just have to chase with the mixture screws, and be back where I started.

By the way, this forum is awesome! Can't say the same for the Holley one...

Cheers,

Robert
Click to expand...

The idle mixture screws should only affect curb idle, and maybe cruise up to 30 mph or so. Above that, the carb is pulling fuel mostly from the transition slots, which are not affected by the idle mixture screws. You should really check to see what your AFR is at 65 mph if you haven't. I've found that the mixture leans out the faster you go on the transition circuit, so if it's 13:1 at 40, it may very well be closer to 14:1, or at least high 13s, at 65, which would probably be satisfactory.
 
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