1992 40hp Johnson running on one cylinder

[bryant526]

Hey guys/gals! I have a 1992 40hp Johnson that seems to being running on one cylinder at idling RPM but not at full throttle. At an idle I can pull the top cylinders plug wire and it does not seem to effect the motor whatsoever, but if I pull the bottom cylinder plug wire it dies immediately. Weird thing is that it sounds like its idling fine and when its out in the water we get 30mph with two adults in a 14' Livingston boat (which I don't think would be feasible on one cylinder). So far I've rebuilt the carbs, replaced the ignition coil, plug wires, and spark plugs and the issue seems to persist, however replacing the plug wires and rebuilding the carbs did seem to help a little bit. On a side note, I originally replaced the plug wires because they were both shocking me when I touched the rubber boot and after replacing them, the one wire for the cylinder that's struggling at idle still shocks me mildly. Any help with this would be greatly appreciated!

 

[juno pierrat]

try spraying/squirting some mixed fuel in carb while idling, if cylinder fires, its still carb problem

 

[jakedaawg]

Compression test.

open air gap spark test.

fuel sample into clear jar.

any spit back out the front of the carbs?

Were orifices cleaned and removed and reinstalled in the carb?

Do you get any change by adjusting the mixture needle? I believe they are there in '92. Could be wrong on that though.

Has the linkage been messed with since the last time it ran well?

The cylinder drop test you are performing tells you the most if you can do it while in gear under load at varying rpms, in my humble opinion.

If you put your hand over each carb throat does that change the running? Do you feel equal suction?

 

[bryant526]

Thank you both for your replies! I have tried spraying carb cleaner into the top carb with no difference.

Compression tests have comeback on the poor side. Both were around 85ish. I didnt have the outboard completely warmed up though.

Waiting to get an adjustable spark gap tester, but I am getting good spark when removing the plug and grounding it against the engine. I am also getting good spark when using one of the light up spark testers.

Fuel sample looks good to me, but I maybe missing something.

Not sure what you mean as far as spit back goes, but I have gotten a mild amount of gas/oil residue on the intake side of the carb.

All orifices were removed and soaked in the carb cleaner solution for an hour before being rinsed off and sprayed out with an air compressor. I'm quite sure the carb is completely clear.

I get changes when adjusting the mixture needle on the bottom carburetor but not the top. I can completely close off the top carb with no change and if I close off the bottom it will die.

linkage has been adjusted.

Hand over the top carb does not seem to change anything and there is some suction. Cant do much more at the moment though because my starter is now stuck in the up position.

I have been doing some more research and have read that a bad crankshaft seal could be giving me the issues that I'm experiencing. Do you know much about those?

 

[racerone]

I doubt it is a crankshaft seal problem.----It should respond to the carburetor needle.----Perhaps revisit carburetor work.----And compression of 85 PSI means a bad gauge or serious motor problems.

 

[bryant526]

I was hoping it's a bad gauge because at WOT with two adults in a 14' livingston we get 30mph, which does not seem like a number we would be getting if the motor was bad. I'll try to find another gauge once I get the starter fixed.