My 30B has developed a tendency to soon decelerate to 600 or 700 rpm from normal 1100 after starting. It does not respond to throttle movement for a minute or so then returns to normal throttle operations. After sailing an hour or two the problem recurs on restart. The engine has approx. 3600 hours and gets regular mx per manual. Fuel tank/system polished last summer. Racor filter appears normal. Anybody have experience with this issue?