OK thanks for pointing out we don't have similar engines. I do not have a water separator. I have an external tank (not built in). I have inspected it for water and there is none, also have drained the carbs into a glass bowl and no water in carbs.
I believe there is a "tilt switch" that will kill the ignition by completing a circuit to ground if the motor gets trimmed up too far (safety feature). Maybe your tilt switch is malfunctioning. You should be able to unplug the tilt switch to eliminate it from consideration. It is usually...
This may either be a large unmetered air source or timing stuck at full advance. Start by verifying the spark advance linkage and trigger arm—if timing is locked at wide-open, the motor will race even with the throttle closed. Next, recheck carb sync and pickup cam settings, and make sure...
Does this have CDI system? (little box that tells the coils when to fire)? I have a 1986 50 hp Mariner that was giving me intermittent problems similar to what you are describing and sometimes it would run OK for a while even. Through diagnosis, I concluded that I didn't have spark to one of...
Is the primer bulb collapsed when it dies? I am assuming not since you have a new tank and fuel line. I am dealing with a somewhat similar problem on my 75 hp but it only runs about 20 seconds at WOT before dying.
I am having a similar problem with a 1991 75 hp Merc. It runs well at idle and up to about 80% of WOT and will run all day long but if I go to 100% WOT it will run there for maybe 20-40 seconds before it suddenly loses power and pretty much just dies. I also have noticed that if I am cruising...