Have Classic Car Questions? Ask an Expert.
A vacuum leak. Closing the choke helps richen the fuel mixture back up some, close to normal.
Did that answer your question? If so, kindly leave me a positive rating, so I get credit. If you have any more questions, go ahead and ask.
Anything that could cause a too lean fuel condition, such as a vacuum leak or the vacuum too low as in the case of a high performance/ high lift camshaft or late ignition timing.
Can you tell me what the intake manifold vacuum is at idle?