Best Way to set the idle mix on a 4160

[steve meltzer]

I've seen some people advise to adjust each mixture screw (from 1.5 turns out) to it's max vacuum. This makes sense to me, but on the Holley video (not Holly does Houston), they say to adjust to max vacuum, but that both sides should be equal. I find it hard to believe, that in the real world you could make both sides exactly equal, and that the max vacuum on each side should be your goal. thanx. Basic question, I know, but....thanx steve

[DanEC]

You can set the idle mixture with a vacuum gage or a tach. I've gotten to where I prefer a tach in recent years but I still use a vacuum gage sometimes. You should tune each side to achieve the highest vacuum or idle rpm separately - going back and forth a couple of times. On most motors the adjustments will end up pretty close to each other - but yeah, there may be a little difference in where the screws end up from side to side.

[steve meltzer]

thanx so much. that's what i suspected...max vac. s

[patrickt]

If you're between 3/4's of a turn out and 1-1/2 turn out the car should run decently. You can also try the old trick of adjusting the turns so that when you pull the rubber plug off the intake manifold port the RPM's stay the same. The most important part is not to have your idle turned up so far that you're too deep in to the transition slot. Or, you can do what I do to get it just perfect......... Make sure your primary butterflies are at the bottom of the transition slot, back your idle screws out about 3/4's of a turn from seated, then adjust the idle speed by cracking the secondaries with the hidden set screw. Then take your car out for a steady slow drive with the throttle lightly applied and steady and feel for your lean surge, which you should have. Back the screws out 1/8th of a turn and repeat until the surge is gone. The object is to have the leanest possible idle mixture setting that allows the car to run nicely.

[steve meltzer]

Patrick, i know we talked about replacing the factory slotted screw for the idle on the secondary. did you use a socket cap (with hex for an Allen key) or what? 1/4-20 or? thanx. steve

[patrickt]

Originally Posted by steve meltzer

Patrick, i know we talked about replacing the factory slotted screw for the idle on the secondary. did you use a socket cap (with hex for an Allen key) or what? 1/4-20 or? thanx. steve

10-32 cap screw. For use with an Allen wrench.

[steve meltzer]

Just wanna confirm...this is a full manifold vacuum port. right? thanx. s

[patrickt]

Yes. As is the small one on the very front of the carb down by the base plate. The little one that is above the passenger side idle mixture screw is ported.

[steve meltzer]

OK, just as I thought. 2 ports (different size orifices) for full engine vac + the one "ported" above the blades. s

[steve meltzer]

OK, got the carb set and the fired up. Hope to set the timing using the "power/last timing advance" method this weekend. For now, it's set at 10° BTDC, initial. I don't see a leak from the intake (yet). Fingers X'd. thanx. s

[patrickt]

Ten degrees BTDC is a nice place to start. We're just trying to get the car to idle nicely, and not leak, then we'll graduate to having it drive nicely. But, since you mentioned timing, of course your total "all in" timing is what's important. I think you have aluminum heads, like mine, and my engine runs best with 35 degrees total advance. So, with my MSD distributor, I have the 25 degree bushing installed along with ten degrees initial timing to give me that total of 35. Ten degrees initial puts less of a load on your starter (which you just might benefit from). I use the light silver and blue spring combination to achieve the following curve. Notice how the advance comes in. This works very well for me and has for many years.

[steve meltzer]

OK, Got it all set up and running well. My base timing is 21, the total, 36. Got the Holley set up as Patrick suggested, with the idle set by the secondary adjustment. Because of the geometry of the Holley and its underlying Edlebrock intake i had to use a hex-head machine screw, not an Allen head, but it's easy to adjust with a 5/16 wrench. But, and there's always a "but", right? It still leaks from the intake. Gonna get some adult supervision to install next. arrgghh. s

[patrickt]

Originally Posted by steve meltzer

But, and there's always a "but", right? It still leaks from the intake. Gonna get some adult supervision to install next. arrgghh. s

OK, you mean it leaks from where it sits on the "China Wall," or where it mates up to the heads, or where the carb/TP mounts to it up top, or what?

[patrickt]

There's a current FE intake gasket thread going on over at FEpower, Looking for some advice on intake gasket

[Gaz64]

Originally Posted by steve meltzer

OK, Got it all set up and running well. My base timing is 21, the total, 36. Got the Holley set up as Patrick suggested, with the idle set by the secondary adjustment. Because of the geometry of the Holley and its underlying Edlebrock intake i had to use a hex-head machine screw, not an Allen head, but it's easy to adjust with a 5/16 wrench. But, and there's always a "but", right? It still leaks from the intake. Gonna get some adult supervision to install next. arrgghh. s

Have you got some pics of your leak?

Oil leak, or vacuum leak?

What bush do you have in your distributor to get 21 and 36?

Gary

[patrickt]

Originally Posted by Gaz64

What bush do you have in your distributor to get 21 and 36?

Not MSD. Their black bushing is 18 degrees and that's the smallest one in the kit.

[tortuga]

One thing i noticed about setting the idle with the secondary stop screw is that if you open the secondaries too much the motor tends to come off the throttle slowly (running on the secondaries?).

On my motor if i set the transition slot square its way too MUCH throttle...Think mine are pretty much covered at idle if i try to balance both ends...My secondaries are tight as frog lips at idle with the primary just cracked. No vacuum leaks, Walker PCV valve set for low vacuum.

[Gaz64]

Originally Posted by tortuga

One thing i noticed about setting the idle with the secondary stop screw is that if you open the secondaries too much the motor tends to come off the throttle slowly (running on the secondaries?).

On my motor if i set the transition slot square its way too MUCH throttle...Think mine are pretty much covered at idle if i try to balance both ends...My secondaries are tight as frog lips at idle with the primary just cracked. No vacuum leaks, Walker PCV valve set for low vacuum.

One thing with a Holley or other 4160/4150 Holley style carb, QFT AED etc, is to check that the primary to secondary link does not jam in the slot as you open the primaries slowly off idle (engine off). This needs to be checked after final hot idle speed has been set. This is assuming that near equal airflow is occuring around all four throttle blades at idle, especially for 4 corner idle carbs.

Some aftermarket throttle bodies have their transition slots too high up the bore.

Gary

[davids2toys]

Very nice, thank you

[MOTORHEAD]

re: sticking carb. Sounds like a throttle plate sticking against the bore .