water from discharge port not constant

[smasher]

I have a Yamaha F40TLRD 4 stroke. water exiting from discharge port is not constant comes out strong and after a while it gets soft for a minute then back strong. Replaced impeller, insert cartridge and o ring. Still the same. Could it be the thermostat?

[boats.net]

Check the thermostat to see if opening and closing properly.

[rkmartin]

Water Pressure

Doesn't the engine have a pressure releif valve? My 90 horse varies from time to time with a new water pump as well. I was thinking the pressure releif valve needed to be changed.