Mid 50’s Johnson 25HP runs like crap. Advice needed

[fleetwin]

The water leak is sure a possibility, but I wouldn’t go pulling that exhaust cover off just on a guess. You could pull the gearcase and try to run the engine, but it will have no load or exhaust back pressure so it might just seem like it is running better….Run the engine normally, pull the plugs, look for droplets of water…Tap the plugs in the palm of your hand also, this helps show the water droplets…Again, I would not go pulling that cover unless you have more solid proof that water is getting into the cylinder(s).
I’m trying to remember which cylinder wasn’t firing correctly…I’m looking at your pictures again, looks like the manifold area that has the sooty residue belongs to the bottom cylinder. I’m making this judgement by looking at the way the crankcase is deflected "upwards" on the left of your picture, and "downwards" on the right….
So the reeds "look OK", are those rubber tank pressure valves OK? Seems like it is time to get back to basics before getting in "too deep".

[hdted]

Corroded reed plate or reeds? Also seems like the top cylinder that’s missing. If top crankshaft seal is bad it could cause fuel charge for top cylinder to leak off through roller bearing. Just a thought. Also I have seen bad head gasket or exhaust cover gasket to cause the problem by leaking water into the cylinder. The plug you are holding on the bottom indicates water getting into the cylinder.

[huntleybill]

ok…I will try running it outside the tank.
Will let you know.

[fleetwin]

quote Huntleybill:

ok…I will try running it outside the tank.
Will let you know.

??

[huntleybill]

Sorry fleetwin….this week and weekend got away from me. I will get to it ASAP.

[fleetwin]

quote Huntleybill:

ok…I will try running it outside the tank.
Will let you know.

I’m not sure just what you mean by "running it outside the tank"…..
Please don’t run the water pump impeller dry…
And again, I don’t think you will be able to judge much by running it with the gearcase removed for the reasons I mentioned previously…
I am confused because the sooty drain relief reed is on the bottom cylinder, the one that seemed to be firing OK…
So, would probably just put the engine on a boat and try to go for a ride to get the needles dialed in better and see how it runs….

[huntleybill]

I didn’t think running it outside the water tank for a few min would ruin the impeller. My thought being that if the problem is that its sucking in water, if it is out of the tank, there is no water and therefore the motor should run fine. If it still runs bad, water may not be the problem. but you already knew that.
Also hdted, compression is 110 on both cylinders, if there is a gasket leak in one of the cylinders, would that not show up during the compression test?

[fleetwin]

It only takes a minute or so of running the impeller dry to damage it, so please don’t run it outside the tank.
Is it not convenient to run the engine on a boat? If not, we could try another approach. Start the engine in the tank and let it warm up so it will be easier to start once it is out of the tank. Next, remove the gearcase so the engine can be run on a sturdy stand with no water. Rig up some sort of hose connection to the water tube inside the exhaust housing….Start the engine with no water running through it, see how it runs, the turn on the water supply to see if its running quality changes. Have a look at the plugs after running with no water, then compare them to how they look after turning on the water supply.
Again, it will be tough to compare running quality between running in the tank and running out of the tank with the gearcase removed….Running it out of the tank with no gearcase removes all exhaust back pressure and the load of turning gearcase components….So, it would be easy to conclude that the "engine runs better" with the gearcase removed, and head down the wrong path.

[vintin]

Being we are throwing everything we have at this motor:

Have you checked the crankcase drain reed system?

Have you interchanged all of the upper and lower cylinder ignition components under the flywheel to see if the problem follows the components?

[Author]

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