Lots of high revs but boat is not moving

[johnglen]

I have a 1990 Sunbird 16' runabout with an Evinrude VRO 90 HP (model E90TLESB). I am experiencing an on/off problem that has just come back after 2 years of no issues. What happens is that when I increase the throttle when cruising fairly slowly, it's as if the motor is in neutral as there is lots of sound and fury, but no forward motion. It is not a spun prop (dealer checked this 4 years ago). I am woefully ignorant of the workings of boat motors and wonder if anyone has experienced something similar and/or if there is a common cause for this problem. Thanks.

 

[Daviet]

Re: Lots of high revs but boat is not moving

As you describe it about the only thing I can think of is a prop hub problem, did the dealer actually scribe a mark on the hub and check t after the experiencing the problem?
Does the lower unit oil have any metal in it?
Does the lower unit seem to jump in and out of gear, feels like you might have hit something?

 

[johnglen]

Re: Lots of high revs but boat is not moving

I don't know for sure, but I don't think that the dealer scribed a mark. The boat is still in the water so I can't check the lower unit for metal. I have experienced a thump that sounds like I hit something, but it happened when going through a weed bed, so I can't think that would be the problem.
When I look back at the invoice for carb repairs/rebuild from 4 years ago, I noticed a comment about adjusting the micro switch (whatever that is) and wonder if that could lead to the motor essentially slipping into neutral?

 

[daselbee]

Re: Lots of high revs but boat is not moving

No micro switch on that motor. And for SURE, no switch controls the lower unit operation. You have a spun prop, I believe.

 

[Chinewalker]

Re: Lots of high revs but boat is not moving

If it is intermittent, could it be seaweed fouling the prop?