Yamaha f150 flushing problems

[Whaaaaat]

Have a pair of 2006 f150 on our dive boat. We have always flushed after use. The right hand engine has never had a strong pee stream using the hose adapter.
Just completed 300 hr service. 300 total hours. There was way too much corrosion at the top of the block around thermostats. So I have been running the engines after use on flush ears. Left hand engine, no problems, piss good will idle all day on the hose.

Right hand won't piss, overheats top of the block is dry and hot. Bottom of block is getting water. This engine won't piss with the flush adapter anymore either. I can get just the slightest dribble.
I pulled the lower today to see what I could, found nothing, hooked the flush adapter up with lower off and plugged the water tube with my finger. Pee stream was strong. With engine tilted all the way up.

New within last 10 hours
Water pump, thermostats, updated poppet,

I'm at a loss for what to do next other than pull powerhead and look in midsection and adapter plate.
Any advice from Yamaha techs out there?

Also when using the boat the right hand engine pees fine, does not overheat, but stream is weaker than left engine.

[RSWORDS]

Some of those motors just plain hate to run on muffs.

Pop the thermostat cover, give the muffs a good squeeze to tighten them up, and see if it pumps water to the stat.

Side note. Done your balance shaft assemblies yet?

[Whaaaaat]

Some of those motors just plain hate to run on muffs.

Pop the thermostat cover, give the muffs a good squeeze to tighten them up, and see if it pumps water to the stat.

Side note. Done your balance shaft assemblies yet?

Anyway to tell what version the balancers are. The boat is only been ours for a few years, but there's evidence that they have been changed. They don't make noise.

As for flushing I think I'm gonna end up with a horse trough or something.

[RSWORDS]

Take the cowlings off and start it. If the dont whine like belt driven blower you are good.

The horse trough is a good idea.

[Whaaaaat]

No wine from them, I always listen for it.

There 25 inch motors so I'm gonna replace the rubber grommets in the water tube extension piece next, even though it looked good. And get a water trough