lean condition question

[yodabiri]

My friend has a 64 ranchero with a 200 ci engine. When the engine is first started, it runs rough a little, but then smoothes out and runs great while its warming up to operating temperature. Once it reaches operating temp, the car starts running rougher and starts kinda surging under cruising conditions. It kinda seems like its leaning out when it reaches operating temp. The choke is the original heat activated choke on the carb. So maybe for some reason the car is running very lean once the choke is completely opened. The main jet in the carb is a 70 jet if I remember correctly from what he told me. We tried retarding the timing a little bit, hoping that might richen the mixture, but it didnt really help any. The carb on the car is an autolite 1100. Does anybody have any suggestions to what could be causing this surging? BTW the ignition is a DUI unit, if that helps with anything.

 

[rbohm]

8) might not have enough timing, or you could have a vacuum leak.

 

[yodabiri]

We tried looking for a vacuum leak, but couldnt find one. What is a good method to find a vacuum leak? Spray some starting fluid in possible places and see if the idle speeds up?

Thanks for the response!