Joebrick

1973 350 L82 4 spd, original quadrajet.

Looking for ideas why my idle wont hold with a warm restart. This is a point where the car sits for a few hours, intake manifold is still around 130F and choke is still open.

When warm, the car fires right up with no touch of the gas. The idle is low.. and if I don't nurse it along..... it will eventually slowly drop down in idle rpm and die. After a few minutes, the idle holds on its own and slowly gets to the point it's back to 900 RPM and all is well.

Hot restart within 1/2 hr no problem. Cold starts are no problem. Drives and idles fine at 900 RPM.

Anyone else experience this? Percolation maybe?

I have a recirc line back to the tank that I know works, welch plugs were checked, vented gas cap installed.

MelWff

Very few carbureted cars start warm without depressing the gas peddle a little.
If you depress the pedal a liitle when doing a warm restart do you still have a problem or does it idle correctly after a few seconds?
How long since you adjusted the idle mixture screws?
When adjusting idle mixture, do you turn one screw in at a time till you get a drop and then turn back out?

Joebrick

Will try the start method you describe with partial pedal and see what happens.

Idle screws I set one at a time to the highest vacuum I can achieve...then reset idle speed to 900 rpm

Rescue Rogers

Mine will restart after being hot without touching the pedal put its afresh engine with great compression....what are you using for a carb? Do you have a hot air choke or an electric choke? If it fluctuates up and down I don’t think it would be an idle set screw. If you disconnect the cable from you throttle linkage will it still do the same...maybe the cable is heating up and expanding and altering the setting slightly? Doubt it but you never know. Maybe a slight vacuum leak that is sealing as it heats up,,,,,just throwing possibilities to check. Has anything been changed lately or tune up performed? Do you have your vacuum advance connected, could be leaking

Mrvettenick

If there's an idle solenoid, check it's operation, and if the connector/wire is OK.

Joebrick

Its a Quadrajet and it fires right up warm, just doesn't want to idle there. No up and down, just slowly drops down to stall. Divorced choke. Vacuum advance hooked up. Idle solenoid works, but I have it away and the idle screw is resting on the carb. stop. Its been doing this for a long time and is more of an irritation since if I keep idle rpm with my foot for a few minutes its fine. I just know its not right.

I even tried non-ethanol gas and no change.

OldCarBum

If it runs fine a couple of minutes after the warm start it could be a slight percolation issue.
Some members have solved this issue by installing a thin heat shield between the carb and intake manifold.
These were factory installed on many models to help solve heat soak issues and were often removed by auto repair shops and back yard mechanics.
You might also try insulating your fuel line and make sure it is as far away as possible to any heat sources.
My 73 bb has had this issue for the four years I’ve owned it and the new engine I’m building will include a 1” phenolic spacer under the carb to help.

Mrvettenick

When it stalls, look down the carb throat to see if fuel is dripping down, It could be a sticking needle/seat, or a high float level.

ddsmith60

As I recall, on a divorced choke, the fast idle cam of the choke assembly gets set by pushing down the accelerator pedal. If you do not press the accelerator pedal down, then you will not have a fast idle. Here is a little check for you. When the engine is in that partially cooled down state, and you look at the choke blade, what position is it in. If it is open, which I believe it will be, press the accelerator down and see if it closes down some. That should set the fast idle cam and provide choke until the crossover heats up enough to open the choke.

Joebrick

Thanks. Did this and the choke is hard open at this point especially in warm weather. No possibility of going into a fast idle. I kind of wish it would fast idle for a bit.

ddsmith60

When I originally got the car, bubba had put in a manual choke handle. I guess he gave up on the divorced choke. When I went back to the divorced choke, I made the rod that goes from the divorced choke coil to the choke mechanism. That way I could get exactly the length that I needed for correct operation. I don't think you have any adjustments available to change the opening timing in relation to temperature. Divorced choke are a beautiful thing when they work right. I changed my fuel system to Edelbrock Pro Flo 4 4150 system because of other carb related issues I was having. I hope you get your issue figured out. I hate when things don't work the way they were designed.

7T1vette

When you "depress" the accelerator pedal prior to starting the engine, you only have to tap it to set the choke (if it will allow change when that warm). Maybe 10% throttle or so. The choke just needs to be released from its present position and tapping the pedal will do that. You do not need raw fuel from the accelerator pump (what you get when you depress the pedal completely).