Water Getting in Top Cylinder Yamaha 40hp Twin

[joesnuffy]

Hey folks I need some help please.

I have a 1995 2 stroke 2 cylinder 40hp Outboard. The problem is that the top cylinder is getting water into it somehow I don’t think it is much just a trace. I have re-surfaced the head using the figure 8 method and checked it to make sure it wasn’t warped. I put a new head gasket on it. The motor will idle if I leave the choke partially on but will not develop WOT. I pulled the head back off yesterday and it is still getting water into the top cylinder which looks like someone has washed the cylinder out no carbon residue on that cylinder. I read of a person having a similar problem on a twin here recently and they suggested checking the inner exhaust cover/plate. Does anyone think this could be it? I also looked hard at the block where it meets up with the head after cleaning and it looks good no warpage or cracked cylinder that I can tell by looking at it hard. I have a good used head coming I thought it might even be cracked possibly I also ordered a new head gasket but I think I will pull the exhaust plate off in the mean time to inspect it.

I also forgot to mention that the compression level on both cylinders is around 173 psi.

Thanks,
Joe

[beerman57]

I wouldn’t be surprised if it was the inner exhaust plate. Salt water motor? Not flushed after use?

[joesnuffy]

The motor is clean as a whistle. Fresh water only very low hours. I think the thermostat was not opening as it should. The water would just spew out of the pee hole like crazy with a bunch of pressure and it comes from the exhaust plate/s. When I changed the thermostat it now comes out as it should. Maybe the high pressure combined with extra heat from thermostat not opening correctly might have caused a leak on the exhaust plate apparatus if there is one. I think I will try and re-torque the 16 bolts on the plate first to see if it improves or fixes the issue. If not I will still have to pull it off and inspect it.
Thanks,
Joe

[joesnuffy]

I took the inner exhaust plate/s off yesterday and they looked to be o.k gaskets looked good with no visible signs of a leak on them. That will eliminate them as my problem of water getting into top cylinder. I am now waiting on my used cylinder head to see if that will hopefully fix the issue. Has anyone ever had a cracked cylinder head on an outboard that was letting the water into the cylinder ?? I have rebuilt this motor because it had thrown a rod and this cylinder head had been damaged with metal debri where the piston had gone up against it using the debri. The motor had ran fantastic for about 12 hours run time until about 1 week ago it lost a lot of power and won’t run high speed so that is when I suspected the cylinder head. I took a picture of it so someone that knows can look you may have to zoom in on pic.

Thanks for the help,
Joe

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[fleetwin]

Not a Yamaha expert by any means…
But, you mentioned this engine had thrown a rod, so there is the possibility of cooling system damage caused when the rod went thrashing about inside the block…
BUT, I am not convinced you have a water leak. I am assuming that the combustion chamber on the left of your picture is the top/problem cylinder, correct? Yes, that cylinder is misfiring/not firing for some reason, but I am not convinced water intrusion is the problem. Do you see actual water droplets on the piston cylinder/head, or is it possible that the cylinder is just being washed clean by excess fuel?
In any event, you can drive yourself crazy trying to look for a minute leak/porous/cracked block head/exhaust cover, etc. This stuff can be near impossible to see with the naked eye.
Let’s try a different method. Get the motor started and running on a conventional flushette. Now, remove the gearcase and start the engine with no water going through it. No worries about damaging the impeller, and you can run the engine for a few minutes at idle without overheating it to see if it is going to idle any better.
If the engine does not run any better with gearcase off, no water going through it, then I think you are on the wrong track with the water intrusion theory.
If the engine seems to run better, then we can look into the water intrusion theory more. But please beware, the engine will definitely run differently with the gearcase off with no back pressure and drag from turning gearcase components. So, it might be easy to think the engine is running better when it is simply running at higher RPM with no back pressure and gearcase drag. You could always connect a hose to your water tube and run it that way to compare the way it runs with and without water.
If this test confirms your water intrusion theory, then I would connect the hose to your water tube and run water through your engine while it is not running. Remove the plugs while the water is flowing through and get a good inspection light to probe the top cylinder in the hopes on pinpointing the actual leak.
Again, have little to no Yamaha experience, hopefully someone who does will chime in….

[joesnuffy]

Your right I have been driving myself crazy looking for a water leak. I am not convinced it is either. I did not see water droplets on the piston nor cylinder head when I removed it. I was also thinking that excess fuel might clean the head off. This is when the problem started. I was putting sound reduction material inside the cover because it had none. Where the hole for the air is in cover to be sucked through to run engine I thought I would make the opening like a 1 inch square hole and make it bigger if need be to eliminate unwanted noise it should have been like a 1.5 inch by like 3 inch hole. When I placed the cover on the motor is and tried to start it is when the problem occurred. Do you think I might have bent a reed valve/s or caused a leak between the case halves? I also read that a bad fuel pump can push fuel into the engine? I have had an engine in the past that did have a head leak and it would run out of water right not in water as you mentioned. I have the boat on water right now it may be time for me to trailer it to confirm or eliminate the water issue. Thank you for your help.

Joe

ps your right the top cylinder is the one not firing correctly. Looks like it has been cleaned.

[fleetwin]

Joe
I think you are right on track, with your foam theory. It surely seems possible that a piece of insulation got sucked in a carb and jammed a reed partially open. And YES, a leaky fuel pump diaphragm can spill excess fuel into the crankcase it is connected to. Is the fuel pump pressure port on the top #1 cylinder? If so, you could run the engine with the fuel line disconnected, the top cylinder will kick in for a few seconds once the fuel is out of the pump but there is still some in the carb bowl. But again, beware that engines usually lean out a bit and pick up RPM as they are running out of fuel, don’t confuse this normal situation with a leaky fuel pump. I suppose you could just bypass the fuel pump and connect your fuel tank hose to the line running from the pump to the carbs, then simply pump the fuel bulb on the tank to keep the fuel pressure up, this will allow you to run the engine longer and evaluate this theory better. Please do not go ripping into that fuel pump looking for a problem unless this test confirms the fuel pump is at fault.
You have had this engine all apart, so pulling the intake manifold back off doesn’t seem too difficult. Pull the air box and carbs first, looking for pieces of insulation that might help confirm this theory.
You can do these tests with the boat on the water, just don’t be a clutz like me and drop pieces in the drink!
I hope one of these two theories proves to be your issue….

[joesnuffy]

I think the fuel pump is mounted closer to the bottom cylinder. I will start with the fuel pump being possible issue first. I will by pass it as you suggested and pump the fuel bulb to see if engine runs better. The sound reducer material I used is the good stuff like a professional grade 3M style with the peel adhesive no foam nothing to get sucked in but it could have still bent a reed valve if the negative pressure was to high. If it isn’t the fuel pump then I will go and look at the reed valves and maybe re-torque crankcase halves. I have cleaned and inspected the carbs which were both working excellent I don’t think it is them. Both high and low jets were clean and both low jet screw adjustments were 1 1/2 out when engine was running as it should be so it could be I bent a reed do to my not wanting to hear a noisy engine.

This is my first experience with a Yamaha 2 stroke but it seems closely related to an OMC outboard engine which I do know. The engine has good fire on both plugs. With the choke on partially and the idle up a bit it will run and when I pull either plug wire engine will die so both cylinders are firing somewhat it just won’t get over the hump to WOT and the top cylinder looks to be getting washed by fuel or water.

Thanks for your help,
Joe

[RICK EICHRODT]

Check for a broken reed on the top cylinder…..same thing happened to me on a 6 horse OMC motor. Drove me crazy. With the reed gone, the top cylinder acts like a pump and sucks the water up into the cylinder from the exhaust manifold dump.

[joesnuffy]

Thanks Guys I will check it today going outside right now to get started. I bet money I bent/broke a reed or reeds when I cranked engine over with to small air opening. I will check fuel pump then reeds.

Thanks means a lot getting help when highly frustrated,
Joe

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