Hi all - Have a 68 Olds 455, 2bbl. Trying to tune the mixture screws right. Does anyone know how many turns is typically turns out to get the right idle? Are they usually the same amount on both side? Is there any downside as to having it not right - meaning how do you know if it is too lean or rich? Clockwise is giving it more gas and counter is more air, right?

I had it pretty good, but then played with it - now it is rough.


Thanks,
Matt

 

Also, I have a 2bbl carb. Does the number of turns usually very different for the 2bbl versus the 4 bbl.

 

Usually about two.

Usually.

Bad running, smells too rich.

Wrong.

Isn't that always the story?

Do you have the Chassis Service Manual? If so, It's all in there.

If not, the section you need is here.

- Eric

 

Do you have a tach or a vacuum gauge? Hook one of them up, I prefer the tach. With engine warmed up at idle, turn the right screw in until the idle drops and the engine stumbles, then turn it out until you get the highest rpm. Repeat on the other screw.

Then readjust your curb idle speed. Repeat your a/f screw adjustments one more time. Both screws should be out about the same amount of turns.

The same adjustment is performed with a vacuum gauge, your looking for the highest amount of vacuum.

 

By the way, in the document, it says adjust throttle to "CLEARANCE", I take it that means loosen it totally?

Also, regarding the choke, is the choke supposed to close? I touched is 2 weeks ago and it would close. Now it does not close totally, just angled close. Not sure if my adjustments affected that - perhaps my fast idle adjustment?

Thanks! Sorry for the dumb questions.

 

The choke will close at colder temps, so if the ambient temp is like here in Texas, 106, then it will be partially open.

throttle adustment is adjusted so that the linkage slides into the hole or snaps onto a stud without moving either the linkage on the carb or the pedal.

Before doing any adjustments, the choke will be fully disengaged with the engine completely warmed up.