According to those #s it's a 15hp
It sounds like it might be getting hot?.
The 90 didn't have a thermostat, check and see if there's one in the system?
They started using them in 92
Get a heat gun and go for a ride.
It also sounds like the tank vent might be closed?
The filter clogging?
How old are the hose and the squeezie?
There 2 screens in the recirc system that could be clogged?
Do a compression and spark test when it starts to break down.
