Poppet Valve Mercury 90hp

After checking the carbs, fuel pump diaphram and fuel line bulb while trying to trace why my 1993 Mercury 90hp three cylinder two stroke was cutting out at 2500rpm, I turned my attention to the cooling system thinking that perhaps the temperature sensor was sensing an overheat situation and cutting out power.

On removing the poppet valve I found one of the two water channels has been corroded into a large jagged hole. It looks like the poppet valve has not been opening and the salt water has been creating another esape route.

Has anyone else experienced this and could they advise me if this is as serious as it looks. I am considering shortening the poppet valve spring to reduce the pressure and allow the water to circulate normally.

Or is this engine toast? Any advice would be welcomed

Re: Poppet Valve Mercury 90hp

Your engine is only toast, if the motor throws a rod. Until then it is repairable.

I am not aware that Merc's have the temperature sensor connected to the switchbox kill circuit. You might like to verify this with a wiring diagram. I had thought they had just a buzzer.

I would make sure the water pump impeller is in good shape (or better yet replace it), before modifing the poppet. You might rebuild the poppet valve as well. Check the thermostat as well.

Does the spark plugs indicate overheating?

Re: Poppet Valve Mercury 90hp

Many thanks. I will check the items you suggest now that the boat is out of the water (Looks like winter is almost here in Scotland!)

The thermostat seems ok but I will certainly be looking at the impeller.

When you say 'rebuild the poppet valve' do you mean me to fill in the hole in the cylinder block with weld or something?

Re: Poppet Valve Mercury 90hp

Do not fill in the hole just yet. You can buy a complete poppet rebuild kit, aftermarket for <$20US. it has the two gaskets, poppet, poppet seat, seal, screw and and diaghram. I would replace all the components, the thermostats and waterpump impeller, and see how it goes.

I guess I am a bit skeptical that the block corroded as you have described, expecially on a newer motor, like you have.

Also, that motor has a high and low speed winding on the stator. Perhaps the high speed stator winding is bad, and you do not have spark above 2500 RPM. it is something to check out.

Re: Poppet Valve Mercury 90hp

Just looked up my friendly Seloc book and feel that I might be getting out of my depth trying to check the different windings of my stator with only my multimeter and limited knowledge to hand.
I think it might be time to call in the professionals.
Thanks again though, your help with the cooling stuff has been great.
Bill