I had picked up a shudder under acceleration in my 49 1/2ton with 216.

I made the cardinal sin of doing two things before testing it out so I'm not sure which was the culprit.

I did find that the vacuum line fitting going into the carb wasn't completely tight but I also replaced the plugs which were starting to carbon up.

Question. When replacing the plugs, I noticed that the plug in cylinder 5 appeared to be fouled. Could a vacuum leak cause one plug to misfire?

Anyway, she is running fine again so hopefully I fixed the problem. Thanks to all.