I would check to make sure that the ignition coil isn't goosed. It maybe functioning just enough when at idle but the ignition system springs to life because alternator is producing a bit higher output. Check all plug wires are clicked in all the way on to the plug and into the distributor cap. The distributor cap and rotor aren't corroded/in need of replacement. Could be a spark plug is no good.
735 is different than a 750, but when I had discovered that one plug wasn't firing as it should, my idle smoothed out considerably. You'd be surprised how well these things can run with one cylinder down.
If it was drivetrain vibration, I would think the problem would manifest itself when moving. I'll do some digging.
Do you have the fly-by-wire throttle or the cable style?