OK, time for some armchar quarterback shots at my problem.

Fully Forged 383 small block in a 63, Dewitts, 5 Speed,, etc.
has a 3310 sitting on a Z28 OEM intake manifold on AFR aluminum heads. Fully roller.
Car runs great. Until I let it sit for a few weeks. Even 1 week is enough for the car to start rough. Today, it felt like it was not getting fuel, but eventually caught.
It catches, but runs rough low RPMs and emits some black smoke out the pipes.I adjust the throttle linkage to keep it running so it will warm up. After 30 minutes or so, with no change, I hop in and drive it around town, After a few miles it gets better. A=Idle slowly edges its way back up where it should be,, and beyond. WHen I stop for soda or petrol, i shut it off, and when we turn it back on, everything goes back to normal. I have to lower the throttle linkage back down to a liveable rpm, and the car is good to go all day long, And the next day too. But let it sit for more than a couple days, its gets harder and harder to want to fire up and run properly.

I am open to reasonable suggestions. I assume its a carb problem.
The crossovers beneath the intake ar blocked, I have a 180* stat, but the engine runs mostly at 160*.

for those first few aggravating half hours or so, it feels like the car s running overly rich, and stumbling on itself .
Open to suggestions on things I can eliminate.
Pulls to the moon like arocket, doent get me wrong, but it is very temperamental under cold after sitting a while.
THX

 

If there is a choke on the carb, my guess it's not set up correctly. Dennis

 

I had a similar problem with the same intake and a 650 AED carb. When you cut your hot engine off the intake under your carb bowls gets 190 degrees or better. That heat boils the gas out of the accelerator pump into your intake. Lars recommended an aluminum plate sold by Holley that fits under the carb. I installed this plate and it completely eliminated the problem. There was a thread in the C3 tech section that covered this topic in detail. Search Lars in that section and it should be easy to fine. Good luck.

 

I am aware of the holley heat shield, and have used them before.
Is the rough running due to low float bowls, and it clears up once the bowls are full?
The electric choe seems to be working, at least its not on when Im having this issue where it seems to be running overly rich.

Its almost like something is stuck and loosens up, or a vacuum leak that seals once warm.
Would a rich condition (too large main jets) be exacerbated when cold? Dropping a main jet is easy to do.

It is strange for sure that it only happens after sitting for week or so.

The heat shield is an easy thing to try.

 

How cold is weather when you do your cold start?

 

Its California, so like 60* !!!

 

When you indicated you were getting black smoke on start up, that could be raw gas in the intake. The heat shield gave me a huge drop in temp on the float bowls. I can let my car sit 2 weeks and gave it one push on the gas and it starts right up. I do not have a choke.

I found an afr gauge to be very helpful. They are easy to install and will help you on this problem. Also, check your oil for a gas smell. How are your plugs?

 

I have an AFR gauge, just havent gotten around to installing it yet. Winter project yeah!

I havent checked the plugs lately, last time I did they were golden brown. More winter project! (I should have looked at them while the exhaust manifolds were off and it was easy)

 

Don,
My hunch is that when the fuel in the bowls evaporates and the floats drop, they are somehow hanging up in the dropped position. That will let excess fuel into the bowl until the floats become unjammed Excess fuel level in the bowl will cause a rich condition.

What you might do is measure the actual float drop to see if it meets specs and verify the floats move freely.

Jim