OK, hooked up my FAST air fuel ratio meter to my 496 Six Pack and did a little cruising. At idle I'm right around 13.5-1. But when I cruise at 20 to 30mph it runs rich in the 11.0 to 12 range. When I cruise in the 60 to 65 mph it's back to around 13.5-1 Do you think I should try a little smaller jet in the center carb to lean the lower cruise speeds out a bit? I'm tryig to find my paperwork from Harms. But I think I had 64 jets installed. Thanks

That issue will probably take some work to sort out. First you need to figure out which circuit you are on and then go from there. You can change the jets just to see what happens but I'd be surprised if that fixes it. My guess is that at low speed you are still on the idle circuit and probably in the transition slot. You might need a t-slot restriction to fix the low speed cruise number.

You might want to lean out the idle mixtures on the outboards and center carbs so it will idle at or above 14.8, that will affect the lower AFR at your cruising RPM, maybe not enough though I had my old sixpak set up on my 518 C.I. pump gas motor so it would run at or above 15.2 at idle and around 14.8 or leaner at part throttle cruise up to 2500 RPM

awhile back someone posted a tuning guide for em, you might see if you can retrieve it or someone might pull it back up, it seemed fairly comprehensive

At least you have the correct tool to fix
Whats vacuum at idle
What power valve you got
What center jets .
?

six pak tuning guide

You need to baseline your set up, everyone wants a quick fix-there is none, no app for your phone either.

195 degree thermostat is required

It's in the guide, please use the guide

I'm saving this

that be it, Tom is the man

Cab Burge, I leaned out the idle a bit. And it looks like that might get me pretty close to where I want to be at cruise. Just need a little more testing/drive time. I'll report back. Thanks guys

If you want to lean it out a tiny bit more you can enlarge the idle air bleeds (the outboard one in the top of the carbs venturi entrance) on all three carbs. from .001 to .003 larger, drill them a tiny bit at a time, don't go big at first I have the solid blanks for the stock carbs. and a pin vise and numbered drill bit set for this type of work so I can fix what I mess up. Hence the advice on going a tiny bit larger at a time, not big.

Well no luck. Idles in the 14.5 to 15 now. And cruises at 60 to 65 mph at 12.8 to 13. But any around town cruising is 9 to 11. The transfer slot is only showing about .040. Can't find my sheet but the power valve and jets where what Mr. Six Pack recommended for his cam. Basically stock. Am I asking too much for 1970 carbs?

No luck = no patience -
Plan on 4 -6 hrs to get this right .
Jets size?
Vacuum ?
Initial timing?
Bobs requirements only a guideline , if all is healthy
his reccomendations should work, BUt.
Every engine different.
chances are youre just jetted to0 fat from
sound of it.
What happens when you floor it. ? And actually doesnt matter.
Did you reAd the link ?
I wouldnt drill anything until youve gone through
checklist.

Ok a little more info. Jet size 64s. Vacuum at idle is right at 14. Power valve is a 6.5. Initial timing is at 18. And this is a 496 not a 440 stroke. I might give 62s a try and see what if anything that does. Thanks

What is your normal crusing RPM and what RPM is it that it is richest at? You can restrict the transition fuel feed circuit to lean that circuit out I've done that in the past to help clean carbs. up. The primary jet will lean the crusie AFR out at the RPM above where the throttle blades are opened more than being on the transition circuit at cruising RPMs ( I hope this makes since ) What are the List numbers on your three carbs? Are your carbs originals or the newer replacement -1 or -2 carbs?
I had my old six pak set up to cruise at 14.8 to 15.3 AFR depending on throttle pedal opening at or above 2100 RPM to 2800 RPM
Carbs. are tuneable It does take some knowledge and work though, sometimes including errors to learn what that motor likes
If your idling the motor with .040 transition slot exposed your not idling on the idle circuit only, your already on the transition circuit Fix that first and then proceed

I can guarantee you unless you are running an extremely mild cam,#62 jets will be lean.

It's a very mild Mr Six Pack cam. .490 lift and not sure on the duration. But it sounds like a 318 running.

It's rich from basically off idle to 30 to 45 mph cruise. I'm not sure on the list numbers on the carbs. Whatever is correct for a 70 auto. I had to buy 2 of them from Tonys parts. And sent them all in to Harms for a rebuild. I'm going to go pull some plugs and see what they look like. Had to order jets as no one sells them locally. (small town living)

Correct, they were built to stock specs (which is all I do unless instructed otherwise by the customer). Maybe try a 7.0-7.5 Power valve, it might be getting a bit too fat a bit too soon.

Your numbers sound worse than when you started. What exactly did you change?

The only thing I changed was I leaned out the idle mixture with the center carb idle mixture screws. They were around 13.5. Changed them to 14.5 to 15. They are about 1 1/4 turns out. I'm starting to think I have some sort of power valve issue. I did have Scott put in 64 jets per Mr. Six Pack recommendation.