Top cylinder not firing

[Kdogle]

i have a 1972 50 hp that is not firing on the top cylinder. I have rebuilt the carbs, the compression is 120+ on the top cylinder. With the motor running I can pull the plug wire off the top cylinder and it does not change anything, I can see fire arching from the plug wire to the spark plug .
If I do the same to the bottom cylinder the motor will cut off, does anyone have any suggestions what may be causing this problem

[Boobie]

Squirt some fuel in the upper carb throat once and see what happens.

[Kdogle]

I used starting fluid have not tried gas

[dnr471]

How was the motor running before you started working on it?

You say that it is not firing, but then you say you see spark when you pull the plug wire when it is running. Is it not receiving spark when cranking or is the cylinder not receiving fuel to ignite? I have learned that "spark" either visually across a plug or jumping from the wire may not have enough power behind it to ignite a properly or over fueled cylinder. Test a spark gap across all of the cylinders first to make sure that you do not have a coil going bad. If your electrical system is working properly, then I would look harder at your fuel system, especially since it sounds like that is what you just worked on.

Fuel, air, spark.

[Kdogle]

The motor would crank out of the water but when you put it in the water it would never crank. So I started to try and find the answer why . I got this boat in a deal so I have no idea about it’s previous history other than it cranked on land when I looked at it and then when I took it to the lake it would not crank . I tried this many times . I was told by a boat mechanic that it was the stator so I had that replaced . It cranked just fine in the yard take it to the lake and it would not crank .