steam from exhaust on Mercury 4 Stroke 90hp

[pizzafanatic]

First of all, my motor is a 2001 Mercury 4 Stroke Carb'ed version originally manufactured by Yamaha.

Problem: I'm getting a significant amount of steam coming out of the exhaust and my motor is not running very well (backfiring when I throttle up and dies when I put a load on the motor).

This is what I've done in the past month:
1) Compression test show balanced pressure on all 4 cylinders
2) Fresh plugs
3) rebuilt fuel pumps
4) Carburetors completely cleaned and rebuilt
5) Fuel filter, water seperator changed and hoses checked
6) Engine oil and lower unit oil changed

So I'm just dumbfounded as to why I'm getting steam and my engine is running well. I have several questions that I'm hoping someone may be able to answer:
1) My compression is good, so does that eliminate the head gasket from being blown?
2) After running my engine during testing, the plugs are tips are now black. What does that mean?
3) With the backfiring that I'm experiencing, does that mean my motor is running too rich?

Thank you in advance for reading and responding.

Bryan

 

[WrenchHead]

Usually when an exhaust looks like steam the mixture is too lean, or it could mean the engine is overheated. A rich mixture exhaust will be black. Backfiring is also a sign you are running too lean. If the motor dies when you throttle up that could also mean you are too lean. One quick way to test for a lean set carb or an air leak in the carb or air leak in the manifold is to put on half choke while the engine is running. If it smooths out and increases RPM your mixture is too lean or you have an air leak. If you put on half choke and the engine starts loping, putting out black exhaust, or reduces RPM then your mixture is probably OK. Then you will have to move on to checking the ignition and timing.

 

[merc850]

Did you check/replace the waterpump impeller?, steam will come out of the xhaust if the flow to the block is low, which will turn a small amount of water in to steam

 

[pizzafanatic]

Did you check/replace the waterpump impeller?, steam will come out of the xhaust if the flow to the block is low, which will turn a small amount of water in to steam

I changed my impeller last year and when the engine is running, it has a strong stream of water. I just removed the lower unit and noticed the coupler above the water pump has a small slit in it. I'm going to try replacing it to see if that eliminates the steam. Fingers crossed. Does anyone have any insight to the first 2 questions in my original post?

 

[racerone]

What are the local atmospheric conditions ?----------Around my area all cars " steam ' from the exhaust in winter.-----------Nobody is pulled over and nobody is concerned.---------So do you see steam or just water vapour ??