Funny Noise 140 Mercruiser

[drvred]

Was running down the lake this evening when suddenly lost power, sounded like it was knocking. I immediately cut the motor off.
My wife said "There was something in the water" although I didnt feel us hit anything.
Jumped in the water and checked the prop, no damage.
Then cranked the motor it was knocking pretty bad, sounded like the the top of the drive. it also sounded like it was going to run away.
I wiggled the plug wires, didnt seem to be loose.
Since we were about a mile from the dock and nobody else in sight I decided to idle in. The boat ran fine, so I sped up-perfect.
Then when we came in to load the boat, the high idle came back, and the wife said the noise returned as she was pulling up to the trailer.
Where the heck do I start? Carb, ignition, drive?
Thanks in advance

 

[Don S]

Re: Funny Noise 140 Mercruiser

What do you mean the "High Idle Came Back"? with the shifter in neutral does it suddenly start speeding up?
As far as the noise goes, I would start by pulling the outdrive, check the ujoints and gimbal bearing, and look for water in the bellows.
Then start the engine (Hook water hose the T-Stat hsg. for cooling) and see if you still have the knocking noise.

 

[drvred]

Re: Funny Noise 140 Mercruiser

Normally the idle is pretty low. Today it was racing whenever it went to neutral.

 

[Don S]

Re: Funny Noise 140 Mercruiser

Is the throttle cable pulling the linkage all the way back to idle? Could be a bad throttle cable causing you high rpm problem, but it won't cause a knock from the outdrive area. You still need to pull the drive to check that.