4 Corner Idle - Should all mixture screws be the same?

[bigboi]

Should all 4 idle mixture screws on a 4 corner idle be the same?

For instance... Should all 4 be 1 turn out?

Or... The fronts might be 1/2 turn and the rears might be 1 turn?

[Vegas69]

Close but not necessarily the same. You are always going to have variations in runner length, heat, and thread depth to seat the adjustment screws. Get it where it has the highest idle on all four corners. Also make sure you have your idle close to where it needs to be before making the adjustments. Also make the adjustments at operating temp.

[vintageracer]

A vacuum guage can also be your friend when adjusting the carb.

[bigboi]

I am not sure why this is happening.... But when I start the car I am at around 700 rpm idle... I drive the car for a bit and then it's at 10-11k rpm at idle. Once and a while it will drop back down.

What the heck is wrong?

I am thinking maybe I am getting air somewhere and this is causing the idle to go up? I checked my linkage and it's fine. I have not removed the carb from the gasket nor done anything with the intake gaskets.

I even put new spark plugs in to make sure all the gaps were set at .30.

The spark plugs look a little white so I am probably a little lean... But this would cause the idle to act funny...

All of a sudden this is happening when I went to make adjustments to the mixture screws.

Errrr.... It's driving me nutz. Any suggestions?

[Shaker455]

Brian,
I got your PM's so give me a shout
Jeff

[vintageracer]

Eratic idle is a great indication that the plastic bushings in the throttle shafts are bad and leaking air. This will cause eratic idle and make it difficult to adjust the idle mixture screws. I assume this carburetor is a older used Holley since you did not mention the make of carburetor causing this problem.

If this is truly the case, replace the bushings. The best and most effective replacement is to drill the baseplaste and use oil-lite type bushings to replace the plastic bushings. This little modification is probably best left to a pro!

[Shaker455]

Mike,
He has a farily new AED unit and it does not have any plastic/teflon bushing installed.

AED and myself buy directly from Holley and one of my standards is to break the new base down and install my custom made teflon bushings to control airleaks and reduce dirt and metal to metal contact.
Jeff

[vintageracer]

Jeff,

Oh well, scratch that idea. I am glad to hear that his carb has this modification. This is a big problem with the Holley's as you know.

Mike

[badbu68]

First make sure the idle transfer slots on front and rear are squared up then adjust your 4 corner mixture screws. A good start is too turn them all in, back off a 1/2 turn, hook up your vacuum gauge, start with the front drivers side and go clockwise adjusting for the most vacuum. Repeat.

[yellow heap]

If the idle screw and seats are not nicked all should be within a 1/8 to 1/16 of a turn.
Are you running a vacuum advance?
If so-ported or manifold?
If manifold(good)your vacuum ,if you idle a 14 inches you want your can to start at 12-13other wise the idle timing can hunt and make for unstable idle speeds.
Also can you take the linkage/cable off and on the carb without moving the throttle arm?
To test if idle is lean-push down a bit on the acelerator pump,if idle speeds up a bit you are lean,if it stumbles you are rich or just right.