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Discussion Starter · #1 ·
I have recently purchased a 1967 289 mustang coupe with a 289 engine with 90,000 original miles on it from a little old lady this car is all original and has a 2100 2b Autolite carburetor, I have replaced all of the plugs and wires points and distributor and rebuilt the carburetor, cleaned out the gas tank and replace the fuel filter. I have had the transmission gone through and everything is looking really good. A dry compression test on the engine gives a rating from 118 to 134 car idles real good. Here is my problem when driving at a cruising speed between 30 and 60 the car feels like its lurching as I cruise down the road, this is a slight lurch and when I gas it it goes away. Can anyone tell me what I need to do to get rid of this problem?

Thanks any helpful comments would be appreciated.
 

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Welcome to the forums, Glen. When describing an issue by sensation, a description can be hard to interpret, so I'll cover most of the likely issues. By feel, a "surging" or "hunting" sensation of power during stable cruise is usually tied to a lean condition. The sensation can be from hardly noticeable and irregular like a shifting headwind, to fairly severe and successive when just shy of lean missing. If the feeling is choppy and almost popping by sensation, that can be excessive ignition advance Burbling exhaust, missing, and even backfires either excessively rich or retarded.

One way to determine rich or lean is to cruise at that problem speed for a few minutes, then shut the engine off and coast to a safe spot off the road. Pull the front spark plug from each side. Clean and snow-white porcelain is lean. Dark is rich. A very light gray or tan is great. Different colors on each is likely a vacuum leak, or an issue on only one side of the carb.

Assuming it's a lean condition, the first question is if it happens at only certain throttle settings and speeds. If so, it may an incorrect power valve, opening and closing right at it's rated vacuum. If it happens at different throttle settings or speeds at stable cruise, then read on.

The lean condition is too much air for the fuel flow, or too little fuel for the air flow. First check is for any vacuum leaks from the carb the the heads, including any hoses or gaskets. Do a search for vacuum leak detection techniques.

I would then verify your float level is set properly and check for any debris or blockages while in there. Then check your fuel pressure and volume. This is assuming the jets that were in there are/were correctly sized. Note that many classics are running lean these days with the mandated ethanol in gasoline, which leans the mixture. If no joy and all settings are as they should be, then re-jetting to the next size up would be the next step to compensate for the new fuels.

If the symptoms are more akin to the burbling exhaust then the same steps apply. If the issue does not appear to be too rich or lean, verify your ignition base timing (initial timing setting). If that's right, and it's the choppy/popping sensation, then check your distributor's mechanical and vacuum advance operation. HTH, and tell us what you find as you go.

David
 

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Discussion Starter · #5 ·
yes I drove it before I started doing this work and I have been doing the fixes in baby steps trying to get ride of the problem. It has improved considerably it was much worse than it it now but it is still there. I will try the suggestions given by David and see where it takes me. Thanks
 
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