1976 Eventide 25hp not running right

[Mike bob]

1976 Eventide 25 hp will start, but idles rough and seems like it's running on one cylinder. Compression 135 in both cylinders. Spark on both plugs. The carb was cleaned and rebuilt last fall. It was running ok in spring, but would need to squeeze the fuel bulb to keep it going. Fuel pump replaced last year as well as all internal fuel hoses. Also, there is some water leaking from exhaust manifold. The motor runs very rough and only goes 8 mph at best and dies out frequently.
I am willing to buy parts and put in the time. I just don't want to start replacing things I want to do it right.
What to do first?

 

[flyingscott]

First thing is replace the exhaust gasket and look for water intrusion in the cylinders.. Be prepared for broken bolts and do a cylinder drop test.

 

[racerone]

Sounds like it is running on one cylinder.------Does spark jump a gap of 5/16" or more on both leads, yes or no ?---Answer that question.

 

[F_R]

That motor has the OMC Lo-Tension Magneto. The Great Deceiver. Even if you have good spark, go in and check the breaker points very carefully. Unlike earlier motors, where each set of points only fired it's associated cylinder, on the Lo-Tension mag BOTH sets of points must be working 100%. One set grounds one end of the driver coil while the other set opens to fire a cylinder.

Yeah, and fix that water leak. That could get serious if it leaks internally.

 

[Mike bob]

Yes spark jumps over 5/16. I will replace the exhaust gasket this week. Also I will check the points.

 

[Mike bob]

Replaced exhaust manifold gaskets. Replaced the points and condensers. Then set the points.

It still runs rough and stalls. Fuel bulb got soft. Lots of black oily stuff in the water after running. Next step??

 

[AlTn]

no cost trial...pull the rubber boots and terminal ends off each spark plug lead...cut ~ 1/2" off ea. lead...reinstall the terminal end and boot..reattach to spark plug and run the motor...did this make a difference?

 

[Mike bob]

Did a cylinder drop test. The engine runs when I pull the bottom plug wire. And it dies when I pull the upper plug wire. What does this mean?

 

[Mike bob]

Trimmed spark plug lead did not make a difference.

 

[Mike bob]

Could it be the coil pack for the bottom cylinder? If so how would I test that theory?

 

[AlTn]

switch the coils...does the lower cylinder run now?

 

[Mike bob]

No. Lower cylinder still does not run after switching the coil packs. Could it be the wires from the magneto armature plate to the coil? And if so, how to test that theory.

 

[racerone]

Perhaps there is an issue with reed valves or lower crankshaft seal.

 

[Mike bob]

Reed valves were clean and in very good order. The carb is clean as well.

 

[AlTn]

notice any signs of water intrusion on the lower spark plug?..water beads?...plug appears cleaner than the top plug?....

 

[Mike bob]

Took it to Pewaukee Lake today. It ran a.little rough and all of a sudden....full power! WOT 22 mph. I have a 14 foot mirrocraft deep fisherman. It seems like everything is fine. Goes down to idle. Wow. I'm glad to have my boat back! I'm not sure what did it, but I know this.motor has been gone over thoroughly. Thanks for all the help along the way.

Happy boating!