I'm stumped. I have a 1989 Mercury 200 HP engine that is overheating while boat is underway (not so much when at idle). <br /><br />I have replaced the water pump and rebuilt the poppet valve. The timing is correct and the carburator is adjusted correctly. <br /><br />I have a large amount of air bubbles that are coming from the lower unit. The air bubbles are coming from the exhaust slits (holes) that are on the lower submerged portion of the lower unit.<br /><br />I have a low water pick-up on this engine (if it matters)<br /><br />The compression is between 120 and 122 on all cylinders so the head gaskets should be OK.<br /><br />I don't know what else to check or replace - any suggetions?
