65 Chevelle 283. Just restored with my 15 year old son. However, when we firststart it and until it reached 190 degrees or so, it runs poorly. Seems to miss, runs rough. sounds like its way out of time when cold. timed and dwell to specs. new cap, rotor, plugs. Ideas???? :sad:

Do you have the proper choke on it? Does the manifold have the heat crossover?

I put on an Edelbrock 4 barrel carb (electric choke) and manifold. I don't really know what the heat crossover looks like or what it is

I put on an Edelbrock 4 barrel carb (electric choke) and manifold. I don't really know what the heat crossover looks like or what it is

I have an electric choke Holley and tried every type of adjustment and it still runs as you described. I finally just tied the choke open and it runs great now :confused: .

In all likelihood your intake manifold doesn't have a provision for a heat crossover so if you were depending on crossover heat to open your choke then that would explain why tying your choke open cured your problem. Your choke wasn't getting any heat and consequently wasn't opening. The solution to running a choke on your car would be to install an electric choke kit.

Exhaust heat crossover = A passage, through the base of your intake manifold that allows the passage of hot exhaust gas to cross from one side of the manifold to the other. There is a port in each cylinder head to send and receive that exhaust gas. That exhaust gas which crosses over goes out the opposite side exhaust pipe.

The crossover is normally accompanied by whats called a "Heat Riser". A heat riser is a valve found on one side of the engine, in the exhaust manifold, which, when the engine is cold, is normally closed.

When you start your engine some of the exhaust from one side of your engine is directed up and across the intake manifold through the "exhaust crossover" by that closed heat riser. "Up and over" ...Hence the term "riser".

This is done to quickly heat the manifold such that the gas in the air stream, going into the engine, stays in its air/gas mixed solution rather than the gas precipitating out of solution. Gas in a vaporous form burns more readily than gas in liquid form does.

If you have a heat riser on your engine you'll note, when you look at it, that there is a flat metal coil attached to one side of the heat riser. That coil is a "Bi-metal" strip of metal wound into a coil.

A "bi-metal" refers to two pieces of metal bonded together each having a different coefficient of expansion when heated. This results in the "unwinding" of the coil of metal as it is heated by the hot exhaust and the concurrent opening of the heat riser valve.

There is normally a counter weight associated with the heat riser which is calibrated to slow the opening of the heat riser valve. It is there to offset the force of the exhaust gas stream which is constantly trying to open the heat riser valve.


If you are sufficiently curious you can open the hood of your car. start your engine and then stand over your fender and watch the heat riser open.
All of this is timed by the manufacturer to operate in such a fashion that the air fuel mixture stays in its vaporous form as the engine warms up. The result is that you get a smoothly operating engine in all kinds of weather.


The down side of all of this equipment is that in order for the engine to stay running when its very cold the choke mechanism raises the idle speed of the engine AND enrichens the mixture by throttling incoming airstream. Obviously this is wasteful of gas and is also a significant cause of air pollution. Thats why all your new cars have computer controlled fuel/air mixing systems. They're far more precise at getting your cold car up and running with a minimum of wasted gas and air pollution.