2001 Johnson 90 Looper Knock?

[Phog]

This question has probably been brought up before, but i havn't had much luck finding any info about it.<br />I recently bought a 2001 Johnson 90 to replace a dying evinrude 90 crossflow. THe motor runs great in every respect, but I'm getting a strong knock out of it when coming down from high RPM (>2800). I've inquired all around and from what i've heard, this is a common thing with the v4's made in the last few years of OMC production.<br /><br />I was just wondering if anyone has any info on this issue...i've been told time and time again that these were still great motors, despite this knock, and that it's normal. Should I try dumping this motor while it is still new? is there any way to alleviate this problem? any ideas on what causes the knocking (possibly prop loading?)...<br /><br />Thanks in advance

 

[Phog]

Re: 2001 Johnson 90 Looper Knock?

I've also been reading through other posts about late-year OMC's, and I've seen a lot of problems regarding lower units on these motors...is my 90 also considered to have lower unit problems regarded as "common"?<br /><br />Thanks

 

[clanton]

Re: 2001 Johnson 90 Looper Knock?

The knock is a deacceleration knock, caused by high vacuum and lean fuel when the throttle is quickly returned to low speed from high speed. The last one I seen, a OMC factory rep changed the mid range jets, which helped some. I sure a lot more can be said about this. Some of the V8s used a vacuum switch to inrich the fuel under these condictions, and I think Merc may have done same on some of there engines.