Nissan 40, Or I'll have to shoot my brother.

My poor brother has a Nissan 40 on a 15' fishing boat that my grand dad gave him. We have worked on that stupid thing for months, taken it to mechanics, etc. Runs fine at idle or half throttle. At WOT, motor skips and hiccups, won't plane boat off. I'm pretty mechanical, done a lot of work on motorcycles and cars. Been through the carb twice (rebuild kit), all new fuel delivery, brand new ignition coil ($300), reed valves good, 100 psi compression on both cylinders, 18 sets of plugs, not running hot, new prop, timing is good, actuator moves w/ throttle, bought the manual, set carb to specs, even tried a new decal for the motor housing. I am either going to have to torch this thing or kill my brother, or myself. The funny thing is that it ran fine the first time we took it out. Yes, the fuel tank is vented. Can anyone help? I will send you a year's supply of budweiser and boiled peanuts. I told him to put 4 trolling motors on it, one one each corner. Or a sail. Please help, for my sanity and so my brother doesn't have to get a divorce.

Re: Nissan 40, Or I'll have to shoot my brother.

Put a pair of spark indicators on the engine and run it. If you loose spark on one or both cylinders at the break down RPM...then its electrical. Otherwise its still a fuel system problem....probably.

Re: Nissan 40, Or I'll have to shoot my brother.

Thanks Elvin, I will try that.

Re: Nissan 40, Or I'll have to shoot my brother.

also index the flywheel making timing marks for #2 and #3 cyl, if its a 3cyl. I cant remember. but you also want to insure that the spark occurs for the proper cyl. my cousin has a 2cyl 40 tohatsu that did a similar thing and we traced it to the rev limiter had mal-functioned. also a pulser coil malfunction can do the same. but I also used a stevens CD-77 to test the output voltages of the pulserss,charge coils and CDI output. have you checked the fuel pump diaphram? they do fail occasionally as well.