Marine: Boating, Sailing, PWC, GPS and Navigation - Johnson outboard 4hp twin 1973 firing on one cylinder

What would be the best approach to troubleshooting this problem?
The lower cylinder is not firing. On rare occasions the motor starts on two cylinders but then reverts to one, usually it starts and runs on one cylinder.
There is a spark, there is compression, and there is a smell of fuel inside the cylinder. The motor has been stored for several years. Thanks for any suggestions you can give.

First swap the plugs ( I had a defective brand new plug ) and see if the top cylender has the problem. How can you tell wich cyl is causing the problem? Use a copmresion gague to check compression both cyl shoule be within 10% of each other. A wet plug on the cyl that isn't working is the best indication of fuel getting in there. Compression, fuel, and spark (at the right time and suffient volume) is all that is required for a 2 cycle.

Many thanks for the reply. I already swapped the plugs over with the same result - the lower cyninder does not fire. How can I tell? I disconnect the ht lead from each plug, if I disconnect the top one the motor stops, if I disconnect the lower one it makes no difference at all. I checked the compression in a rather crude way - I took the plug out and put my thumb over the hole and pulled the starter. The compression seemed good enough.

I will check more on whether the fuel is getting there and maybe buy a new pair of plugs.

Thanks again.

try switchen plug wires around if prob moves to other cylinder it could be wire or coil

So what was the outcome???????????/

Since the last post is five years old. we will probably never know.