This is a new issue, but my ‘77 L48 auto has recently not started as well the second time around. I can fire it right up after sitting for a week or two with no issues; it turns right over and sits comfortably at 700 rpm. But after I do 5 miles down the road to the store, I’ll come back out and it wont start near as well. I can get it going but It takes a minute and it seems to struggle to get up to idle and stay there. After about 5-10 minutes it seems to work itself out. Almost as if it’s harder to start after it’s warm. Any ideas what that might be?

 

Are you applying about 1/4 throttle before turning the key?

 

Yup. I do that both cold and warm and get the result mentioned above.

 

Sounds like you are in the situation where things aren't quite warmed up enough for the car to start without some choke but the choke is open because its opening coil is warmed up (assuming you have an electric choke). The instructions for my Edelbrock carb advise that the coke setting may need adjusting to suit either summer or winter conditions.
Is the engine settling to 700 rpm straight away when you start it cold? I would expect it to be on the fast idle setting when cold and rpms to be above 1000 - 1200
Pump the pedal a couple of times (this sets the choke closed and the throttle on the fast idle cam) and then foot off for starting my vette.
In a half cold situation the fuel can condense out of the incoming mixture on the intake walls and the engine won't start.

 

Thanks! This gives me a good starting point for diving in this weekend.

 

I agree about the choke but I dont think its set correctly for the weather change or just not set correctly at all. I know Ive had to adjust mine in the past as the weather changed from summer to fall if I had set it during the summer.....And when you first start it, with the choke set it should be idling above 1200 rpm with the fast idle cam engaged. I would investigate the choke setting...I believe mine has a couple of steps on the cam and it opens in stages as it warms up.

Or when you come out of the store, pump it once then just hold the pedal to the floor as you crank. If it a slight flooding issue then it will over come that with more air, obviously let up off the throttle once it starts. Another indication of a slight flood is that it just keeps cranking. When I had the fuel boiling issue I would hold it to the floor and it would spin over a couple of times then fire up. Sounds like your description

good luck

 

Remove just the air cleaner lid for a visual.
On a cold start I press the throttle pedal to the floor and let the pedal return slowly one time this sets the fast idle speed.
After pressing pedal one time make sure your choke plate is completely closed. Start car observe the position of the choke plate. It should have opened somewhere between 1/4" - 5/16" some fine adjustment may be needed for a smooth cold start fast idle.
The emissions decal under the hood calls for 1600rpm for your L48 A/T on a cold start. IMO that is way too high, I set mine at 1200-1250rpm.
Depending on ambient temp on my hot air choke style system the choke plate goes full vertical (open) below 45* about 5 minutes and over 60* under 4 minutes of runtime.
I never leave the house for a cruise until I see the EFE actuator change the state of the exhaust heat riser.
Once I see the heat riser change state I just tap the throttle pedal and it drops off fast idle. In park it idles about 625rpm and in drive about 500rpm, with A/C on it bumps up to about 800rpm in drive.
I now know the car is at its normal operating temp.
Once my car has warmed up I never need to touch the throttle again as long as it is still somewhere near normal operating temp on a restart.

 

If you can, pull the complete air cleaner housing a take a semi close photo of the side of carburetor choke side.