How to Diagnose a Cylinder Misfire 

I had the same problem on my 125merc 2stroke, I did a link & sink, cleaned the carbs, & still would not get on plane, rebuilt the fuel pump, & still nothing! So it narrowed itself down to the accelerator pump, & sure enough, that was the fix!

@@mlipsey66 Mine was the float needle seat in the top carb backing out!!! Pulled the intake cover off and sprayed gas into the carbs and the boat sped up when spraying into the top one! Inside the carb was like-new clean, it was just the seat that backed out.

clogged/restricted fuel filter?

Did you figure it out?

@@SamandKadenGoPlaces yes and no. I fix it. But then it screws up another cylinder. One I track that down #6 goes acts again. I have not had all 6 cylinders fire reliably since.

Here is the procedure in my service manual : "Test spark plug leads for continuity. Calibrate ohmmeter on low ohms scale. Attach one ohmmeter lead to each spring terminal. While wiggling both spark plug covers and the entire lenght of the spark plug lead, the resistance should remain near zero ohm. Replace spark plug lead if your test result vary." Also inspect the insulation of the spark plug lead to see if there is a crack section. The rubber insulation of my bottom cylinder was cut by the cowling latch when I bought the engine. Continuity was good on the ohmmeter, but the spark was probably arcing out of the insulation. If the spark plug leads are good, check your ignition coil. I had to change one on my 1996 25hp. Since then, it run great! I hope it help.