Yamaha 90 2 stroke - Water Pressure Issue to Cylinder Wall Corrosion

rkmurphy

Recruit
Joined
Jun 23, 2013
Messages
1
Hi all! New to the forum but have used in the past for its wealth of information. I'm having some issues with my 2001 Yamaha 90 2 stroke and was hoping you all could possibly help. A little background.

I used to get around 15-25 psi and my tell tale let loose like a race horse. However, within the last year it has dwindled to a weaker tell tale and less than 10 psi...even to the point where I'm overheating at WOT and higher RPM. Even though the tell tale is weaker than in the past, it is still quite strong, which is strange.

I had a repair shop flush some Bright Bay Descaler (similar to Rhydlyme except no acid) in the outboard but it didn't work. So I got tired of worrying about it and removed the head and exhaust cover. It was pretty bad...lots of corrosion and gunk but no visible blockages.

Back pedal a little bit, I had the boat out yesterday and, toward the end of the day, the motor started to hesitate and run funny. Made it back to the ramp okay and was able to open it up but it still had a funny idle.

After removing the head, I noticed the bottom cylinder was corroded as well as the cylinder walls. The corrosion looks fresh. The head gasket looked fine but the head cover gasket had a hole in it around the bottom cylinder area, which to my knowledge doesn't affect anything. I could be wrong, though.

So, where do I go from here in trouble shooting this issue? Poor water pressure and cylinder/cylinder wall corrosion...I'm hoping this will be relatively simple but, we all know it never is!

Thanks in advance!
 

Toddboat

Petty Officer 2nd Class
Joined
Jun 13, 2013
Messages
134
Re: Yamaha 90 2 stroke - Water Pressure Issue to Cylinder Wall Corrosion

I could be wrong, but I would think that if there's a hole in the gasket, it could allow water from the cooling channels to leak into the area of the cylinder. I would clean out the corrosion and replace the gasket and see what happens. You may get instant satisfaction if you see an immediate pressure increase.
 
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