97 Evenrude 115 De-Acceleration Noise

[jamesk191]

I have a 97 Evinrude 115 ocean pro that makes a weird noise after high speed de-acceleration. The noise sounds like something plastic is hitting the fly wheel fins. The noise is more predominant during hard de-accelerations as opposed to easy de-accelerations. I have pulled off the cover, exposing the fly wheel, but see nothing. Could the noise be coming from intake de-acceleration (reed valve)?? The noise has never gotten worse, nor changed pitch. Also, the noise is only heard under load. (I have the manual) Any suggestions?

 

[Dhadley]

Re: 97 Evenrude 115 De-Acceleration Noise

Welcome aboard the board!<br /><br />It's called "de-cell knock" and its exactly what you describe. The motor "knocks" on hard de-celleration. It doesnt seem to hurt anything and some 60 degree motors do it worse than others. You can make it quit by engaging the primer. Sometimes a cooler plug will help too. Just stick with Champions.<br /><br />Good luck!

 

[jamesk191]

Re: 97 Evenrude 115 De-Acceleration Noise

Thanks for the reply!Do yo believe the "de-cell knock" is caused by a bad reed valve? The manual doesn't explain how to service them. I do know that they are behind the carb. I called the dealer and found that they are $85 each (4 total) for my motor. Do you know how to check if they are bad? Are they replaced easily?

 

[Solittle]

Re: 97 Evenrude 115 De-Acceleration Noise

james - If it ain't broke - - - - -

 

[angus63]

Re: 97 Evenrude 115 De-Acceleration Noise

De-cell knock is caused by pulling back on the throttle quickly, hence changing the ignition timing quickly (retarded). Until the rpms of the motor come down to match the new timing position, the motor is firing too early and causing the knock. No cure. Slow down gradually unless its an emergency and you will not notice any knock.

 

[Duck Loads]

Re: 97 Evenrude 115 De-Acceleration Noise

This is something that I have never fooled with before, but you might read the following copied from an article in Bass and Walleye Boats talking about a 60 deg v-6 150:<br /><br />The downside to our project was a little-known phenomenon called deceleration knock, which is a common trait for Eagle engines. Lacking proper carburetor jetting, the outboard will audibly “knock” (similar to a car “pinging”) as the throttle is released, typically when backing off after a high-speed run. This Intruder was no different. The solution is slightly richer high-speed jetting, which Montague provided. After the adjustment, the knock almost disappeared at all throttle settings. This is not something to be overlooked; if ignored, you risk detonation and expensive piston and cylinder damage. <br /><br />Good luck

 

[clanton]

Re: 97 Evenrude 115 De-Acceleration Noise

More fuel in the midrange will help. The V8 OMC and some Mercs have a fuel valve controled by a vacumn swith that will increase fuel under high crankcase vacumn, which happens when you jerk the throttle back. On some of the OMC V4 and V6 60 an increase in the midrange jet would stop the knock.