Re: Nissan 90hp two cylinders running very rough...
I had a similar issue with my 1996 Nissan 90 hp. It ran finefor 30 minutes then ran at about 1/3 speed. No alarms of Oil, or water. After rebuilding the 3 carbs still the same. I went to a hotter plug, for NGK the lower number the hotter the plug, but this did not help, I switched to semi synthetic 2 stroke oil and it seem to run a little better. So I pulled the carbs off again, this time I realized that I had not removed and cleaned the high speed jets. To do so you will see the bottom of the jet protruding into the carb throat, looks like a small brass tube.Just push itdown with a screwdriver to remove.after unsrewing the main jet. When I removed each one they were 90 plugged up. Clean carbs again along with the high speed jets and it rans at full speed but smoked a bit much. I read the service manual on oil pump adjusting, just needed to align the match marks on the oil pump to the oil control lever and little smoking now. So as a recap, clean carbs Completely, use semi synthetic oil and adjust oil pump flow. Note* if you drain the oil tank and you should, when switching to the semi synthetic you must first pour 1 gallon of oil into the tank and let it flow to the oil pump, then loosen the oil pump bleed screw to purge the air out, tighten the screw and you're good to go. Hope this helps
