235's have a really nasty habit of the valves sticking in the guides when they sit idle for a while. Pull the valve cover and squirt a liberal dose of Kroil or some other penetrating oil on the valve stems, and work the valves up and down with a pry bar. They should move freely, with no tendency to stick. If a vacuum gauge fluctuates a lot at idle, you've got an intake valve leaking a little.
Jerry

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