1990 90etld Overheat/Injection Problem

[jdhnwfl]

I was running most of the day at 3/4 throddle or less and ran fine. I went to WOT for about 5 min and the motor shutdown. It acted like it was starving for fuel. Pulled the cover and paint around exaust manifold had gotten hot. Went to ramp on 1/2 throddle with no problems. Got home and checked buzzer, it was week but working. Installed a temp and removed the T.stat. Took out and ran good except hearing engine noise at WOT. Thought oil inj. problem so added oil to gas and ran fine at OWT for the rest of the day. Flushin at home and noticed no water comming out of the two exaust ports but water at the prop hub. I also found the oil level in the tank lower. I assund I have a blockage in the water jacket. Am I missing something or should I start removing parts looking for blockage. Where should I start. P.S. I always have always had good water pressure at the tatle-tale.

Any thoughts would be great!!!!!

[99yam40]

Check your compression, sounds like it possibly was running lean, hot, and may have hurt a piston or cylinder if you can see evidence of over heating.

Put a good thermostat back in. These motors need the stat to get the water to flow properly through the motor.
Check/ replace PRV if you have not done so already

Replace water pump if you have not done that lately, just to make sure you are getting proper water flow.

When was the last time you cleaned your oil system and tested it?

All motors need maintenance to keep running properly, check to see what all Yamaha recommends and when.

[jdhnwfl]

125 top cyl, 120 cntr, 115 bottom. W/P & t-stat 8 months old. What is PRV?

[jdhnwfl]

I also tested the T-stat on stove and worked good.

[mitch]

It is the water bypass valve but for some reason yammy call it a poppet valve
i guess a translation thingy.