idle speeds

[k20]

Hey guys Im just fiddling with some of the finer points on my truck. At idle in park it is idling at 11-1200 (too high and I want to bring it down), when I drop it to drive its dropping to 700ish (Id like about 800). If I bring the screws up to 800 in gear its idling at like 1300 and when you shut it off, it doesnt like to and diesels along because I think its starting to get into the mech advance. It also wants to pull through the brakes at an 800 idle. Im starting to think I may need to loosen up the converter a bit. *sigh*

Also, what can I do air conditioning related? With its current idle speed, in gear, click the AC on and it wants to drop to around 500rpm (not happening). This is the first time Ive had AC with my carb, what did the carb trucks do to make up for the reduced idle speed with the AC engaged?

 

[badmix]

SOmething you have to keep in mind. I know on my HOlley carb. it has 2 idle adjustments. one is curb idle and one is reg. idle. You have to find a mix between the two and you need to get your A/F ratio correct.

Here is how I tune my carb. I simply stick a vacuum gauge in the engine bay and adjust the a/f to read between 15-20hg. as you adjust the a/f youll adjust the idle.

 

[broncoman6524]

I *think* the factory Quadrajet carbs had an actuator to bump the idle when the a/c kicked on.

 

[dyeager535]

Is this a Quadrajet?

 

[k20]

nah BG speed demon, didnt know if there was someway to adapt something stock to it.

 

[fried_guy]

The big difference between park and drive idle speeds, the diesling, and the jumpyness when idling could all be indications of a vacuum leak. Check that out first.

And also, adjust the idle needles for highest vacuum reading in gear. Then add as much timing as you can until it gets hard to start or you notice pinging... then back off a few degrees. Both should increase your idle speed. Then lower the idle speed with the idle screw.

This should keep a lot of the transfer slot from being exposed as well.

 

[Fabrimacator21]

Is the choke shutting off?

 

[4-play]

If your engine has a long overlap cam with little idle vacuum, it can cause the same symptoms. If that is the case, you may need to loosen the convertor. When both of my electric fans come on, it wants to kill my engine at idle. The Quadrajets had an electric solenoid that kicks the idle up a bit when the AC comes on. You may be able to adapt something like that.

 

[k20]

Yeh I think at idle Im only pulling like 7 or 8" of vacuum cause of the cam, I know when I swapped this iteration of the 496 in I had to go to hydroboost cause the vacuum assist wasnt working too great anymore.

No vacuum leaks, I played with it a little this afternoon, we'll see how it is in the morning.