I've read a lot on this topic, but I'm still learning here's my question:

I have new a 440 with decent sized cam and a NEW sixpack set up. Car starts up quickly, runs at 180-185 degrees F and shuts off clean. Mechanically sounds like a beast.

CAMSHAFT: 241/247@.050" .540/.540 lift. (hyd.flat tappet)

I'm trying to get the center carb to idle "within the idle circuit" but I'm having a little trouble.

When I put a vacuum gauge on the "spark port" of center carb at idle, it's still pulling vacuum...so it seems I need to turn the idle adjustment screw out to close throttle blades more...but if I did this enough to get a zero reading on the gauge the engine would die as it cant idle at 600rpm.

I've advanced the timing to the point where I'm not sure I should go much more...about 22-24 degrees INITIAL at 850-900 rpm. I was hoping to stay about 12-15 initial.

I started the idle circuit screws (center carb,both sides) at 1.5 turns out and tried to turn them out a bit more and watched the vacuum gauge (this time on manifold vacuum) and the needle just moves around with the slight fluctuations of the idle. Basically, I'm not confident in the reading on the gauge with it moving around.

What should I be doing with the idle circuit screws? How should they effect idle? Is it too early to adjust them knowing I'm not running 100% off the idle circuit on the center carb?

I was hoping I wouldn't have to modify the throttle blades (drill holes in them etc) to get the car idle within the idle circuit, so I'm looking for answers.

Advice?

Thanks!

iirc there's an adjustment on the secondaries to open the throttle blades a bit. Then you can drop idle idle speed screw on the center carb.

Awesome...now I just have to find them!

Thank you, that just may solve my issue.

-Dan

Ok, I found those little adjustment screws on the outboards. Obviously you can only adjust the front outboard idle screws and apparently have to remove the rear outboard to adjust it.

By adjust them out a little, the rpm did increase, but I didn't do it too much as I'm sure I'm leaning out the mixture when I do this.

I will remove rear outboard and adjust them out just a tad too (like the front) and see if I can get fully into the idle circuit.

I don't want to lean out the mixture too much either, as I currently have stock jetting and might be on the lean side already. (considering my cam, heads, compression etc).

You can make up for the leaning out with the center carb mixture screws. See if you can get your idle speed and ported vacuum where you want it. Why do you think you need lower vacuum than you already have on the vacuum port? What is wrong with the way it runs, now?

I've read that on the spark port, (not intake vacuum) if you are pulling vacuum on the gauge, than you're not completely in the idle circuit on the center carb. As I close the throttle blades on the center with the idle adjust screw, the vacuum on the spark port continues to decrease.

Once I have the engine idling where I want it with the spark port vacuum reading at zero, then I'll know I'm idling on the carbs idle circuit.

You need to adjust the outer carbs. idle mixtures gently in all the way and then back the needles out 1/3 to 1/2 turn out from bottom out (that means removing the rear carb. to work on it or remove the front and center carbs to work on the rear idle mixture screws ) Make sure to disconnect the secondary linkage and adjust that so that both sets of butterflys(front and rear carbs.) are closed at idle with the center carb butterflys closed all the way also Then set the center idle mixture screws out from 1 1/2 to 2.0 full turns and see if that helps My old low deck six pak would idle that way, same thing with the replacement 1971 440 carbs I bought to compare to my original 1970 440 six pak carbs.

Out is richer, not leaner.

And,until the ends are right center adjustment will do little or nothing.

All you guys are misunderstanding his question.

His problem is, the engine is not getting enough air to run on the idle circuits alone. He is opening the center throttle blade to far to get idle rpms higher but then he is on the transfer circuit. You can not adjust the outboard throttle blades to allow more air at idle like you can on the secondary throttle blades of a DP. This is a common problem with six pack setups

That's a common problem with all carbs. once you get 1.5 turns out on a mixture screw that's at the approximate limit that that circuit will carry, rpm is down, so you crank on the throttle setting and get you extra fuel. Once you give the engine the required fuel for good idle he won't need the extra throttle opening for rpm. In my experience with the six packs 5/8 out on the outboards and that will typically give you enough adjustability on the center, again up to 1.5-1.75 turns out. If the engine is still climbing in rpm, you may need to go more than 5/8 on the outboards. my

No fricken way does that engine run close to right with 12-15* initial. Get rid of that notion. My 340 with a 241 at .050 cam has 24* initial. Starts up in 100+ degree weather with a flick of the key.

It's going to want in the 20's, where you are. Let the engine tell you, not some notion or desired number that you feel is correct.

Thank you for that, that may be the case. It fires up instantly right now and sounds great, so my timing might be very close to being where it needs to be.

Thanks for the great info here guys! I feel like I have the info now to dial these suckers in!