1966 rough start and idle

N
Joined
Jul 24, 2017
Thunderbird Year
1964
I bought 1966 thunderbird 390 engine which starts rough and after a few minutes it warms up it is still rough but not as bad. It drives well for a couple of miles then when I come to a stop it feel like it want to choke out, but it seem to be fine I step on the gas. I’ve replaced the carburetor with an Edelbrock 1406, PerTronix 2 and a Pertronix coil. Any suggestion on what might be the cause for the rough start and idle.
 
J
Joined
Dec 2, 2022
Thunderbird Year
1963
I bought 1966 thunderbird 390 engine which starts rough and after a few minutes it warms up it is still rough but not as bad. It drives well for a couple of miles then when I come to a stop it feel like it want to choke out, but it seem to be fine I step on the gas. I’ve replaced the carburetor with an Edelbrock 1406, PerTronix 2 and a Pertronix coil. Any suggestion on what might be the cause for the rough start and idle.
Check the Power brake unit check valve or a leak in the hose connecting to the PB.
 
64ZCODE

64ZCODE

Active Member
Joined
Aug 18, 2018
Thunderbird Year
1964
Sounds like a fuel/air mix problem. You can eliminate possible vacuum leaks by disconnecting and plugging vacuum lines that connect to the carb or the intake manifold. You could have a manifold intake gasket leak.

Was the carb you installed new or used? An old carb with air leaks or out of adjustment could cause what you're experiencing.
 
Ward 57

Ward 57

Active Member
Joined
Aug 14, 2019
Thunderbird Year
1957
Did you have the problem before you replaced the carb and is that why you replaced it? It sure sounds like a vacuum leak to me. The trick is to trace it down. Mine turned out to be a broken vacuum line at my wiper motor and it was so brittle it just broke off when fussing under there.
Get a can of carb cleaner and when idling spray around the base of the carb and intake manifold. If it smooths out you know where to look.
Ford loved vacuum controls until electric servos became reliable. As stated above, try to disable any vacuum lines at their source and see if that helps. Then trace any rubber vacuum lines, the weak spots are at the connections.
 
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