Cooling stream from piss hole suddenly erratic

[bigtexan99]

Took the boat out last week and the telltale stream from the water cooling line was erratic.

I had previously relocated the stream to the side of the boat near the throttle, so I routinely check the stream during operation. Normally its hot and steady.

This time it was spurting on/off, then over time would mostly be steady with occasional spurts. The temp of the water was hot / normal.

After the engine was off for a few minutes, started the engine and could feel AIR coming out the hole for a few seconds before the water started spurting.

What should I check first?

 

[Sportster-2001-951C-Stock]

Does this only happen at low speed, underway with 50% or more throttle, after a long high speed run, any other detail?

How about the engine block cylinder drain, if this was clogged with sand the engine would tend to have reduced cooling flow and possible hot spots due to inadequate cooling, boiling water in the cylinder cooling jacket would displace water exiting the pisser while looking for the nearest exit (top of manifold exit, air, gasses, steam rise to the top).

So I'd at least confirm the block drain isn't clogged or restricted.