There is a tohatsu 9.8hp outboard motor which should produce a jet of water out from the cooling outlet when the engine is running, but sometimes doesn't. When the engine is started, (seemingly) randomly, we get one of the following:

• water cooling outlet is dry. no jet.
• water cooling outlet is steady, but weak (shoots maybe 6in away. series of droplets)
• water cooling outlet has a strong jet (shoots 2feet away. continuous stream)

There's a workaround when there is no jet (or when it's weak): Shut off the engine, wait 1 minute or less, and restart it to re-roll the dice. Usually it takes one or two restarts to get a jet.

What's the most likely cause of this?

Other details:

• The motor is maybe 3 years old, and otherwise works reliably.
• The current impeller has maybe 300 hours on it, max.
• Motor is used exclusively in salt water. Lifted up whenever it is not in use.
• The owner's manual describes the jet as an "overflow" jet