Overheating on Yamaha F30A

Hi .
i have a Yamaha F30 A outboard (F30AMHD) 2001-2002 ?

I have a problem with over heating . Engine starts at the third pull runs rough for about 30 seconds or so then settles down and sounds fine a few blips of the throttle and a little roughness appears the cooling flow is looking good at this time. However the roughness gets worse as the engine gets hot and the cooling flow seems to slow down and then the engine runs very rough missing quite a bit the cooling flow seems to slow down more then the over heat light comes on . The whole thing lasts 5to 8 min max and it is running on muffs from a garden hose do struggle to get the mufs to stop leaking as well. The exhaust gasses do seem to be a bit white and steamy but again not sure. No water in the oil and everything about the unit looks normal . I am thinking either head gasket ? Or maybee just water pump????

Any ideas help etc very welcome.
Thanks

Re: Overheating on Yamaha F30A

Water pump will not cause the missing so a leak down test for a 4 stroke, leaking head gasket should show up on that test.
test the spark and timing
if no problems found then if maybe fuel related.
But over heating is totally different Water pump, thermostat, clogged passages, etc