Idle help needed

[Johnnyz453]

I have an 83 k10 and im trying to get everything dialed after the engine rebuild. Its a Sbc 350 with a 4x4 cam, flat top pistons, dart heads, edelbrock performer rpm intake, and a brand new quadrajet bought off jegs.
Everything was running right but it was idling high in park but dropping when put in gear. Found out the cable linkage wasnt returning all the way and you could pull back on it to drop rpm. After giving it some throttle and then pulling it back a few times it finally is where it returns now.

The problem is now it idles at 500 rpm in gear and drops to 400 in gear and it doesnt want to stay idling when in gear. The idle screw is turned all the way in so i cant turn up the idle anymore. Dont know why it would be so low with the screw turned all the way in. Since the trottle plates are open more than usual because of the idle screw it wants to diesel when turning it off. Killing it in gear helped but still had a bit of dieseling. It was set at 10* initial but when i dropped it to 8* it seemed to run a bit better. NEED SOME HELP KINDA QUICK.

 

[chengny]

Everything was running right but it was idling high in park but dropping when put in gear. Found out the cable linkage wasnt returning all the way and you could pull back on it to drop rpm. After giving it some throttle and then pulling it back a few times it finally is where it returns now.

I'm pretty sure you mean that the throttle linkage (rather than the cable linkage) was binding. There is no "cable linkage" just the accelerator cable that is connected to the throttle linkage. But aside from that, the rest sounds about right - for an engine that is idling excessively high. If the transmission is in P or N, the engine is uncoupled from the drivetrain and there is no load on it at all. Without a load, the sky is the limit for idle speed.

When you move the gear shift into a position other than P/N, the transmission hydraulically couples the engine to the drivetrain. But when you shift into a drive gear, you also generally have your foot on the brakes - which prevents the vehicle from moving. Engine RPM instantly drops - it can drop dramatically if the idle speed was previously very high - as it tries to move the unmovable vehicle. The only thing that keeps the engine from stalling is the slip allowed by the viscous coupling (read - torque converter). With a manual transmission, when the clutch is released, it forms a solid mechanical coupling. So, if the brakes are applied when the clutch is released...the engine immediately stalls.

The problem is now it idles at 500 rpm in gear and drops to 400 in gear and it doesnt want to stay idling when in gear. The idle screw is turned all the way in so i cant turn up the idle anymore. Dont know why it would be so low with the screw turned all the way in. Since the trottle plates are open more than usual because of the idle screw it wants to diesel when turning it off.

I don't know how far open the primary plates were being held open by the sticking accelerator cable/throttle linkage, but it must have been quite a bit. Apparently the plates were being held open at least more than they can be now - by using the idle speed screw. Because now (provided you didn't change anything else), with the idle speed screw set all the way in, you are unable to reach the RPM you had when the linkage was sticking.

I am not sure it has ever run correctly. Here is why I think that:

With the sticky linkage, you were artificially keeping the RPM up - just as if you were pressing on the accelerator. You solved that issue, but now - due to the plates no longer being held open externally - the idle speed has dropped way below spec (i.e. 850 RPM).

Since it is a brand new carburetor you should assume that it is in good shape internally - and you probably are reluctant to start tweaking it (I wouldn't touch it until everything else has been checked).

Couple of questions - and I don't mean to be a dick when I ask them:

1. The Rochester Quadrajet is a spread bore carburetor and needs to be mounted on a compatible intake manifold. They have standard spread bore intakes and dual purpose intakes that will work with either a spread bore or a square bore carb. Either of those are okay - the only problem would be if you are using an intake manifold designed for only square bore carburetors. You did get a Performer that accepts spread bore carbs correct?

2. The new carburetor probably came with a stack of flange mount gaskets for use with different types of manifolds. One little hole that is covered - and shouldn't be (or vise-versa) can have a huge effect on idle speed - off-choke idle in particular. Are you sure you chose the correct one for your current setup?

 

[Johnnyz453]

The intake manifold is for a spread bore so thats fine. I have a spacer inbetween the intake and carb but its meant for the quadrajet. It came with 2 gaskets but one was thick and one was thin. I put the thin one on since i already had the spacer on.

The part that confuses me is that before when it was idling high if you messed with the curb idle screw it didnt change really anything.

 

[Jrgunn5150]

You need to check for vacuum leaks.

How old is your balancer? Is it marked for timing?

 

[Johnnyz453]

Checked for vacuum leaks yesterday with spraying starting fluid around intake and carb gaskets. Couldnt find any. Has a new balancer and was checked to see if it was right. Used a degree tool too and the cam is spot on.

 

[Jrgunn5150]

Where are your idle mixture screws at?

 

[chengny]

The part that confuses me is that before when it was idling high if you messed with the curb idle screw it didnt change really anything.

Without being there, I can only guess. But from what you describe, it would appear that is was simply because the throttle arm was being held in an off-idle position (by the sticking linkage/cable). It was stuck far enough away, that the tip of the idle adjust screw was unable to make contact with it - even when it was screwed in as far as possible:

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I know you want to believe that your low idle condition is somehow related to a throttle actuation component. But I think the high idle speed condition was a red herring - it's unrelated and distracting you from the real issue. If it were me, I would admit that it's time to look elsewhere.

The fact that the throttle plates are jacked open confirms:

1. That the idle adjustment screw is contacting and moving the arm

2. The arm is rotating the shaft and

3. The plates are secure on the shaft.

That's all that the throttle actuation group is designed to do.

 

[Johnnyz453]

Havent messed with the idle mixture screws much but it was set at the starting point. Totally forgot to hook up the vacuum gauge. Im pretty sure the Idle screw was always touching but i could be wrong. Iv driven it a bit and in park it idles between 500-400rpm and barely drops when put in gear.