70hp Nissan compression 1989

[Scm68]

My 70hp has been running rough at full throttle. Sounds like maybe fuel related. I had the carbs cleaned but problem continued. Checked compression and numbers were 150 and 90. Any ideas what might cause such differences?

 

[pvanv]

What is your model? Likely an NS70A2? Compression differences are typically the result of uneven wear in the cylinders, or coking of the rings in the low-compression cylinder. I would decarbon the motor and re-check the numbers.

Then, for the WOT misfire, if it's still an issue after the decarbon treatment, go through the whole setup. Be methodical. Verify fuel delivery and carb float settings, check link and sync, make test coils and plug wires, and of course clean and gap the plugs. Use your Factory service manual as a guide.