'92 Yamaha 85HP Power Problems

[bazil]

This problem has baffled me. I can run full throttle for about 20 minutes then the bottom cylinder(of the 3) cuts out. I remove power to the motor via a battery switch...then reconnect power, start the engine and it is back to full power for a somewhat shorter duration. At some point the bottom cylinder stays out for good. The next day everthing is back to normal until I run full throttle for more than 20 minutes. What could it be? I've trouble shot the coils and they're good. It doesn't seem to be overheating. Is it the CDI pack, voltage regulator or something else. Has anybody ever had this problem? Any suggestions would help.

 

[JB]

Re: '92 Yamaha 85HP Power Problems

Howdy, basil. Sounds a lot like what electronics techs call a "hot short"; a component that fails only when it gets hot. Mechanical devices can do the same thing, as can hydraulic (carb parts). They are a double barreled bear to troubleshoot, because as soon as you shut the system down they cool enough to start working again. If that is what it is, it is likely to be in the ignition system. We old-time, save-a -buck techs find it by switching parts between cylinders until the trouble switches. It's time consuming but economical and reliable. Start with the plugs, then coils, plug wires, etc. If you have no luck with the ignition system, go to carbs, then any other parts that are unique to the troublesome cylinder.<br /><br />Hope that helps. Good luck.<br /><br /><br />------------------<br />JB