My experience with this symptom is crank bearings. When cold everything stays tight and sealed, after a while of heating up from old growly bearings the crank develops play in the bearings, an air leak develops from crank seals not able to stretch far enough with the play in the crank bearings and the problem never goes away or gets better. I went through all of this on an old sea-screwed. Replaced all electrical hardware, carb kits, gaskets, changed settings, at the end of the day the crank bearings were the culprit. I bought the ski used and it had to be a problem child its whole life. Was never taken apart from the day of manufacture so the bearings had to be bad from day one. The pto bearing cage was literally missing three balls, as in never had them from day one assembly. No damaged cages, no broken parts, they were just not there or anywhere in the motor. The ski had a history of trashing stators too. The flywheel which sd called a mag cup was very close to the stator, when the ski would load up on power the battery light came on at the end of the day. The crank would push down so much in the missing bearing section it would open up a big air gap at the seals making it nearly impossible to keep running and the "mag cup" would impact the stator. That was my first and last sea-screwed lol
