1989 Nissan 90hp won't plane when warm

[Jake1995]

So I have a 1989 Nissan 90hp on a 16 foot Nissan boat and it is having some problems. First time off the landing I can get it to plane no problem but only stays up for a minute or two and once the motor is warm it won't come close to getting up. It's like it revs up fine to about half throttle and then any further then that you can hear it just bog down and have no power. I have checked the things I know how but by no means am I a mechanic. Compression is 132, 131, 131 in cylinders top to bottom. Spark is strong and fuel lines are not obstructed and tank is venting fine. Carbs are also clean. Beyond that I don't really know where to look. Any input is appreciated!!

 

[ondarvr]

Check for spark when its acting up, you can use a timing light.

 

[Sea Rider]

BTW, Welcome to Iboats,

That's a 28 year oldie. Will need a digital multimeter with DVA Volts reading capabilities to troubleshoot all ignition electrical parts correctly. When electrical components gets old could work fine when cold, when heats up can short, open, whatever happens to them when more throttle is in demand and OB starts to miss.

Other culprit could be a bad head gasket condition, it's dried, cracked, hardened, doesnt seal well head against combustion chamber, worse at 3/4 to full throttle in which could have more water intrussion in cylinders. Head gaskets are not eternal and I'm 101% sure that head gasket was not retorqued to factory specs soon after break in period ended and subsequently from time to time.

For the moment, installl a new spark plug set gapped to 1.0 mm and check if got better.

Happy Boating

 

[211libwtfo]

Anti-siphon valve.?!!!?.

 

[Jake1995]

Thanks for the ideas. Finally broke down and took it to a shop and they told me it was getting a false signal and rev limiter was kicking in only allowing 3500rpm and shutting down one cylinder. Couldn't get parts so they disconnected the Rev limiter. Worked great and got on plane fine but first time out I realized it wasn't a false signal because once on plane for a few seconds it stops pumping water. Back to the shop it goes. Had a brand new water pump put in last spring so we will see if it was faulty parts or whole other problem.