1975 70hp evinrude cowl/air intake prob???

[andy w.]

Hi.Have a really puzzling problem.My 1975 70hp evinrude ran fine last year.This year it had a couple issues.One was that it had a sharp miss that would come & go,got 3 new coils,problem gone.Also had low power at high speed issue at same time & thought it would go away with the replacement of the coils but it didn't.When you get up on plane you hear the motor rev through its rpm range like normal,gets to full revv for like 2 seconds then it slows down on its own.Throttle plates opening all the way.No cable issues.No carb issues.I'm a mechanic up here in the north country,been through the motor& it runs great till your at open throttle.If I take the cowl off it screams...put the cowl on& it bogs down.An air problem but I dont know what the major malfunction is.Cows all clear.No blockage or anything.Any help is greatly appreiciated.Thanks Andy

 

[tashasdaddy]

Re: 1975 70hp evinrude cowl/air intake prob???

99% bad base gasket, it is sucking exhaust up from the lower unit, not enough oxygen for combustion.

 

[andy w.]

Re: 1975 70hp evinrude cowl/air intake prob???

Hey,you might be on to something.took it for a test again tonight & noticed water bubbling up around the shift shaft through the grommet& water further down underneath engine.Couldnt really see too well what it was about but i'm sure its not supposed to be there.It's a good foot above the water level. Would the vacum in the cowl be strong enough to pull the water in with the air at open throttle?Seems like things have water droplets on them when I take the cowl off.I work on autos more than boats.Tough dealing with a problem I haven't seen before.Would the base gasket keep the water&exhaust out or do I have another problem too?