I am having an issue with the idle speed on my L69. I will try to describe the problem as well as I can.......
Car starts fine, (but if it has sat unstarted for a few days, it has to crank a while to get fuel to the motor. Once started, it starts flawlessly whether hot or cold.) On cold start, choke kicks in and the car idles high as expected. Once it begins to warm up, blip the throttle and it will idle down to approx 850 rpm. The main issue I am having is that whenever the throttle is opened, whether by pedal, or by hand, the motor does not immediately return to 850. It wants to idle quite high for about 10 - 15 seconds and slowly return to normal idle speed.
It has acted this way since I have owned the car.
The motor was supposedly freshened by a PO, but I have no idea what may have been done. It sounds like it has a bigger than stock cam, I've been told that it sounds like a W30 cam. I have heavy weights and heavy springs in the stock dizzy, running only centrifugal advance, no vacuum. Initial timing currently set @ 12-13 deg adv. It pulls very strong at WOT and does not run hot.
What I have done so far:
Carbs completely restored (which helped smooth the idle but not cure the problem), checked for and found no vacuum leaks. Removed and restored throttle linkage from firewall, checked for smooth operation and no sticking or binding. Checked dizzy, weights move freely.
Looking for insight for what else I can check.
Thanks,
Randy

 

The surging coupled with the dry carb after a few days points to leak-down from the carb. Did you test to see if the plugs are still sealing correctly?

These bad boys: http://www.highperformancepontiac.co.../photo_02.html

 

Is the carb linkage returning all the way to the stop? Is the choke pulling off all the way? And there is a vacuum actuator on the car, is it engaging and keeping the throttle open. My other thought would be a vacuum leak at the base of the carb due to the mounting hardware needing to be retorque'd.

On the car sitting for a few days and having to crank it a while, 10-15 seconds is about normal.

 

Throttle linkage is returning to the idle position. Have checked for vacuum leaks, 3x2 carbs are fully restored to virtually brand new (not just rebuilt). Choke is not interfering with idle. The car will idle fine, but if you blip the throttle either by hand or pedal, the idle does not settle down to normal until after some time has elapsed (10 - 15 sec).
I didn't think the bowl on the center carb should run dry at all?
Could there be a distributor issue of some kind? Timing chain?

 

Sometimes the hot air compensater will cause this issue. I know some people plug them up and it runs great.

 

Choke not being fully open [weak spring] is my first guess.

Closely examine the mechanism to see what exactly is changing when the idle drops and behaves properly- is it the actual throttle butterfly moving, or is the timing changing? Should be one or the other.

Make sure the choke coil is allowing the fast idle cam to come off completely, and that the FI cam is in fact doing that. Take the FI cam off for a test if need be.

At hot idle position, take the throttle rod off the carb and ensure that it is not propping the carb open a bit. If it's auto trans, the kickdown switch and related links can all be stick or binding. Throttle rod off the carb and re-test to produce the symptom should rule that part in or out.

 

just curious, are you running a holley elect fuel pump?

did you check to make sure the distrib wieghts are returning and not hanging.
New carbs don't mean that they are perfect..could have been dropped during shipment ..knocking the float setting off. seen it before....so don't get hung up on "new carb" theory. I run 3x2's and my carbs do not leak down. they dry up from not starting for a long time but don't leak down...

before you start the first time, did you look down the carb and see if the accel pump is squirting fuel. it should after several pumps.

do you see anything that would indicate the floats are out of adjustment, inside center carb wet above nozzles? just a thought.....

 

you did check for vaccum leaks?? have you check every hose coming from engine, not just at the carb... did you check all three base gaskets for leakage.
sorry another thought.....

 

 

make sure the green linkage is adjust properly. you can temp hold up the rubber plug and the see if the helps.

 

Put a timing light on the engine and watch the timing mark as it comes back to idle. If the weights are sticking, it will show up with the light. If not it is definitely in the fuel system.

 

that is the idle vent valve, operated by the accel rod, if you have tthis vent. it should be opened at idle. if not it will sometime create a vaccum in the fuel bowl and cause an unstable idle speeds. I have mine open all the time.

sorry for all the messages, just think of something else after I hit the "send" button....:.)

 

As far as I can tell, everything externally on the center carb seems correct at at idle. Throttle blades closed, choke fully open. Only vacuum line is for the PCV valve, and that is brand new along with the valve itself.
Appreciate the ideas, I will do some more investigating tomorrow with regard to the timing.

 

Did some more tinkering and detected what I thought was an intake gasket leak. (motor sped up when carb cleaner sprayed along junction of intake and heads) Spent half of the day replacing intake gaskets, fired up motor, still acting weird. Hmmmm? Olds buddy helping me with my project says - is there supposed to be a fitting in that hole (on the center carb). I swear I looked those carbs over several times and never noticed the missing fitting (for the vac adv line, which I don't run). (Now hanging head in shame) Buddy screwed plug in to open hole and voila! Carb starts acting normally............ it's a bitch getting old............ guess I need to make an appointment with the eye Doc.........
Thanks for all of the suggestions.
Randy

 

Glad you found it. We're not old, just older.