Re: Very Rough Idle at Startup '55 Caribbean

Posted by Marty or Marston on 2018/5/25 9:12:20
With the air cleaner off and while the engine runs rough for the first several minutes, the front carburetor made an unusual air flow noise when it would run poorly.

I performed a cold engine compression check (throttle wide open) and found values ranging from 110 to 123 psi. I drained a quart of oil from the engine and replaced it with a quart of Marvel Mystery Oil. When I started the engine, it ran rough like before and settled down after 3 or so minutes. I let the engine run for about 15 to 20 minutes to get warm.

After allowing the engine to sit for 4 hours to cool, I started it up and it ran fine. I ran it long enough to get good and warm. I repeated the process about 4 hours later that day. The next morning after sitting over night, I restarted the engine and it ran fine with no rough idle. I have since tried it now three different mornings without any idle issues.

I'm guessing that the problem must have been a slightly sticky valve or maybe an issue with a hydraulic lifter.

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