Please don’t replace the pump, unless you can prove it is NG….New pumps are very expensive, and I really don’t think a leaky pump is the issue. Is the mag plate jumping around causing erratic igntion advance? Perhaps something is dragging on the flywheel magnets causing the mag plate to move around.
Are you sure this thing is running consistently on two cylinders? You may have ignition issues causing one cylinder to fire intermittently which will certainly raise and lower RPM. It’s kind of hard for me to judge without actually hearing the engine misbehave…Have you tried replacing the plugs? Just cuz plugs are new, doesn’t mean they are any good…
Anyway you can post a video?
