engine: 28R707 1120-E1 030826zO. single L head i believe

mower: murray 309008x99a

history: previous owner indicated all was wrong was old (bad) battery.

replaced/worked on:

-battery

-muffler

-spark plug

-cleaned carb (float was stuck open, big gas mess when i put some in)

-oil changed (after big gas mess)

-tightened engine mounts (they were loose)

-vent cap checked on gas tank, not plugged

engine starts fine. but runs very loud and excessive vibration. loud like i want to wear ear plugs. but runs.

after running 10 or so minutes, as it warms up real good, it looses power and eventually dies. while hot, won't start. won't turn over actually, acts like battery doesn't have enough juice to turn it over. and its seems pretty hot. when cools down it does turn over and starts fine.

measured valve clearances: 0.010 on exhaust, 0.007 on intake.

thoughts?