My setup is a 350 with holley 4160 vac. sec. 670cfm carb, HEI, no EGR. Stock Holley jetting from the factory.

I have noticed that my engine seems starved for gas when the cold weather (sub 20 degrees or so) started.

It idles rough and really slow (sometimes dies) and when you stab the gas at cruising speed it stumbles for a second, until the secondaries kick in.

I put some HEET in and carb cleaner but the problem still seems to be there a little (it also warmed up to around 30).

I also noticed I lost 1mpg on the highway.

How cold does it have to get for the jets in a carb to make the engine run real bad? Any suggestions on how much bigger the jets should go? Or what jets?

 

Carbs were around for 100 winters before electronic fuel injection became common, and nobody made seasonal jetting changes.

 

while that is true, it's less then helpful... Gas "gels" at what, -80*C? If it's that cold, you're not alive anymore anyway.

You will lose mileage in the winter, get used to it.

Not familiar with that carb in particular, but I imagine it has a choke? electric or otherwise? Is it working ok? Have you checked it?

 

makes ya with you had a factory smog aircleaner from the '70's-80's that picks up heated air form around the exhaust manifold and mixes it with incoming air so that the air entering the carb is not so bitterly cold during the winter.

Unfortunatly the ZZ4 heads do not have provision for exhaust EGR passges to bring heat up to the carb plenum.
This manifld heat really helps vapourize fuel during the winter. Liquid fuel will not burn.

A choke would go a long way to improving winter drivability.

 

The factory snorkel air cleaners are helpful in cold weather. Unfortunately, very few of them clear the bowls of a Holley.

The SA should have an electric choke.

 

put a Q jet or edelbrock on for winter time

good luck

 

My edelbrock does the same thing, my quadrajet did the same thing. One being that on both carbs the choke either didn't work or was disconnected, and two on my intake manifold gaskets I had the heat riser ports that lead under the carb blocked off. My first set of intake gaskets didn't even have provisions for it. The second set of gaskets had these metal tabs that I used. My car runs like complete butt until it warms up. But I rarely drive it in the winter so not having heat or a car that runs like butt doesn't matter much.

 

Hook up a heat-stove for it.