88 yamaha 70 rev limiter prob?

[Houseboat er]

We have a 88yam 70 hp that sometimes hits 3 grand them misfires and slows down. Back off the throttle hit it again it revs fine but maybe next time reved up will do the same misfire
Did all the normal stuff , plugs comp test carbs cleaned adjusted ,coils tested, therms switch tested, oil level switch tested all are good any and all wires checked for cracks ,shorts ,loose or corroded con all is well it seems any ideas?

 

[99yam40]

Re: 88 yamaha 70 rev limiter prob?

fuel pump leaking into crankcase is one of the things that comes to mind

but testing like manual says to make sure all is in spec with the proper test equipment is the best way to find out what the problem is
Need to know if you are loosing spark or if it is a fuel issue

 

[Houseboat er]

Re: 88 yamaha 70 rev limiter prob?

Not sure if spark is lost or what. Will check the fuel pump as well. I see it is pulsed direct from crankcase. When the engine does this miss all the plugs come out wet and oily.

 

[don diego]

Re: 88 yamaha 70 rev limiter prob?

We have a 88yam 70 hp that sometimes hits 3 grand them misfires and slows down. Back off the throttle hit it again it revs fine but maybe next time reved up will do the same misfire
Did all the normal stuff , plugs comp test carbs cleaned adjusted ,coils tested, therms switch tested, oil level switch tested all are good any and all wires checked for cracks ,shorts ,loose or corroded con all is well it seems any ideas?

Spark advance lever sticking?

 

[Houseboat er]

Re: 88 yamaha 70 rev limiter prob?

All the linkages cams etc all move at the right time and adjusted to spec in yamaha manual

 

[Houseboat er]

Re: 88 yamaha 70 rev limiter prob?

There seems to be no rhyme or reason to it it happens right at start up sometimes other times after slowing down then try to throttle up it miss fires. After it clears up it runs great no slobbering

 

[99yam40]

Re: 88 yamaha 70 rev limiter prob?

get the proper test equipment and check peak voltages in and out of CDI to see if they are in spec while problem is there