Carb tuning

[Chad Witham]

I attempted today to do some carb tuning, mostly idle mixture baseline stuff attempting to help my vacuum out, and make the idle quality a bit better. Nothing major just screw turning, well I screwed it up and now it has little vacuum and idles like crap. Anyone have a good baseline procedure so I can start over. It was running fine until I tinkered.

 

[BeepBeepRR]

Well first off we dont know what carb you are talking about. Edelbrock, Holley etc etc. If its a carter/edelbrock I think seat all the way in then out 1.5 turns as a base on both. If its a holley
Edelbrock

Holley

 

[Chad Witham]

Sorry my bad, Holley 750 Double Pumper

 

[68 HEMI GTS]

Warm the motor up, one at a time back out an idle screw a bit. Slowly turn it in, when you hear a noticeable change in the idle back it off 1/2 turn. Work your way around the carb a few times.

 

[71Beeper]

First disconnect & plug the vacuum advance hose (if you use one).
Then, hook up a vacuum gauge to the manifold port (usually at the front of the carb) or directly to a fitting on the intake if you have one.
Engine fully warmed up, set your idle (800-900 rpms).
Then turn the idle mixture screws in or out to get the highest vacuum reading. You may have to re-adjust the base idle after that.
Don't forget to reinstall the vacuum advance hose.
Holley's are the easiest to setup.

 

[Chad Witham]

So since we’re talking about vacuum is 10 as good as I should expect with a bigger cam?

 

[Crackedback]

How big is the cam? If it's in the 240@.050 range, 10 could be ok.

Make sure it has PLENTY of initial timing on it! 10* is NOT a lot.., that's stock 318 territory.

Baseline on a holley, lightly bottom the idle mix screws and back them out 1.25-1.5 turns. Keep all of them equal, whether 2 or 4 of them.

In general you want highest vacuum leanest point. With an auto, you usually have to fudge that a little to the rich side, screws out an extra 1/8 turn or so.

 

[Chad Witham]

How big is the cam? If it's in the 240@.050 range, 10 could be ok.

Make sure it has PLENTY of initial timing on it! 10* is NOT a lot.., that's stock 318 territory.

Baseline on a holley, lightly bottom the idle mix screws and back them out 1.25-1.5 turns. Keep all of them equal, whether 2 or 4 of them.

In general you want highest vacuum leanest point. With an auto, you usually have to fudge that a little to the rich side, screws out an extra 1/8 turn or so.

Cam is a crower 31204 grind hydraulic flat tappet, it's .474/.480 218/227 @.050 on a 108 LSA.

 

[Crackedback]

not big at all. 16ish on initial should be in the range for that one.

 

[Chad Witham]

Thanks CB.

 

[Crackedback]

Just a guess that should pull 14-15in at idle of around 750.

Timing first!