Mercury deceleration knock

Chris St.Clair

Recruit
Joined
Oct 3, 2003
Messages
5
I just bought a 2001 Mercury, 200hp,25 inch shaft, saltwater, carburated motor. It has been rebuilt so I had to do the double oil break in deal for the 1st 10 hrs. It ran fine for the 1st 8 hrs. and then I started hearing a clattering noise that I thought was coming from the lower unit. It does not do it during acceleration. Only when cruising or when slowing down. The shop where I bought the boat says it is deceleration knock and that it is common. If so why did it not do so for the 1st 8 hrs. and won't it damage the motor eventually. Any info. on the subject would be appreciated. :confused: <br />Texas50
 

werdna

Seaman
Joined
Sep 9, 2003
Messages
57
Re: Mercury deceleration knock

The story is,<br />The is a ratchet gear which drives the LU. When it is under load it is engaged tightly and doesnt make a noise. When you cut back on the revs, the gear slips in and out, which creates the clattering noise. We have a 115hp 2002 Merc which does exactly the same. It isnt a problem, and is common with almost every merc. The chances are that it did make the noise in the first 8 hours, although you didnt notice it! :D
 

Chris St.Clair

Recruit
Joined
Oct 3, 2003
Messages
5
Re: Mercury deceleration knock

werdna, thanks for the info, but I would have heard this, it's loud. I sat right beside the engine while someone else drove the boat and didn't hear anything. Now you can hear it from in front of the console. I read an article about deceleration knock last night and it is caused by improper high speed jet setting in the carb. The only thing that changed from when it didn't knock and when it did is the gas that I put in it. I'm hoping that's the problem. Any input is welcome.
 

werdna

Seaman
Joined
Sep 9, 2003
Messages
57
Re: Mercury deceleration knock

texas50 - then it sounds like there may be a problem :)
 
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