Weird noise from 90 hp

[bJOHNSON]

I have a 1999 Johnson 90 hp with a 17 pitch prop. 5300 rpm at WOT. When I decellerate from WOT or from any substatial speed my motor makes a slight grinding noise. Im not sure if its a grinding noise or if the engine is missing. When I put my 19 pitch prop on it I get 5000 RPM at WOT and the noise is less noticable. A mechanic told me it is a clutch in the Lower unit and it is normal. does this sound right. My boat is a 16 foot crestliner superhawk.<br /><br />One more question I had to jump the motor the other day as I left the radio on in my boat. I heard that this is bad on the powerpack is that true.

 

[bJOHNSON]

Re: Weird noise from 90 hp

A little more info the motor was on a 16 foot alumacraft and the noise was also less noticable. Long and short I crashed that boat into a a shipping lane buoy and totaled the boat, and my upper jaw on the gunnel. After a month of my jaw being wired shut I am back to normal. Lesson wear life jacket and kill switch, was i knocked out of the boat and boat kept going. I was darn licky. Anyway the motor was fine but on the new boat the noise is more noticeable. With the hull geometry the boat does not slow down as fast as the other one, coasts longer. The mechanic told me that the prop is being forced to turn faster than the engine during fast deceleration. This would also explain why it is less with my 19 pitch. It makes sense to me but I just want some more opinions and piece of mind. motor run great at every RPM.

 

[The Marine Doctor]

Re: Weird noise from 90 hp

The problem you are describing, I have heard from Merc's and Mercruisers as they are made to ratched. When you pull back on the shifter...is it comming completely out of gear? The installer may have adjusted the shifter cable wrong when installing the engine on the new boat.<br /><br />TMD

 

[bJOHNSON]

Re: Weird noise from 90 hp

I guess that is a possibility, however the boat shifts in and out of FNR fine and never hesitates with the normal clicking that you would normaly get with a stretched cable. What I am describing is slowing down but not coming out of gear.

 

[bJOHNSON]

Re: Weird noise from 90 hp

found a topic under (knocking noise) this post says it is a stack fire. HELP

 

[Solittle]

Re: Weird noise from 90 hp

Enter stack fire in the Search function.

 

[bJOHNSON]

Re: Weird noise from 90 hp

must be missimg something I only get 3 posts one which applys to me. I just want to know if this is going to screw my motor up. That question was not answered in the Post that was similar. Thanks

 

[ob]

Re: Weird noise from 90 hp

If stack fire noise is indeed what you are experiencing,the posts were pretty clear as to the remedy.<br /><br />#1- If your situation occurs when you suddenly dump the throttle from wide open or mid speed to idle ,it will not allow the engine to slow down as quick as the ignition timing position.Slow down more gradually. <br /><br />#2- To remedy the condition if it occurs during gradual decelleration from wide open or mid speed ,you can richen the midrange orifices or reduce the size of the air orifices depending upon which applies to your carb set-up.

 

[DJ]

Re: Weird noise from 90 hp

bJOHNSON,<br /><br />Boat throttles are not like automobile accelerators. You can't tip in/out on a boat like you do in a car.<br /><br />The boat throttle/shift should be moved "quickly" to get the boat into gear. Once that is done, all throttle motions should be performed smoothly-no sudden motions.<br /><br />I think you are hearing the prop turning (with boat forward motion) thus overrunning the clutch in the lower unit.<br /><br />Work on smoothing your actions between different throttle setings.

 

[Dhadley]

Re: Weird noise from 90 hp

On some 60 degree models you will hear what the engineers refer to as "de-cell knock". Overpropping does seem to help lessen the noise on decelleration as you have discovered, but will shorten the life of the motor dramatically. Engaging the primer also seems to help lessen the noise too. <br /><br />It doesnt seem to hurt anything but it can be disturbing to hear. We've taken many motors apart that were doing it and never found any damage. Engineering was working on an enrichment kit at one time. It activated the primer when the throttle was reduced.<br /><br />Just make sure you use the proper fuel (87 octane) and Champion plugs.<br /><br />Good luck!

 

[bJOHNSON]

Re: Weird noise from 90 hp

Sound good thanks alot couple more???<br />am I over proped at 5000 RPM at WOT<br />and would this shorten the life of the engine. One more does this engine have a clutch over run that was talked about. Thanks for the help so far

 

[seahorse5]

Re: Weird noise from 90 hp

the 90 does not have a ratcheting (overrun) clutch in it. Chances are the cable is not adjusted correctly in reverse so it is not engaging the lugs on the gear and clutch dog fully. If the gearcase was off recently, someone may have put it on with the shift rod height setting out of adjustment.<br /><br />If you don't have the factory manual that explains how to do the adjusting, find a QUALIFIED tech to do it for you. There also may be wear already on the parts or slop in the linkage that no amount of adjusting will take out.

 

[Hooty]

Re: Weird noise from 90 hp

I'd say you were over-proped. You should be spinning at least 5600 and preferably 5800rpm. Dhadley pointed out, over-proping will help with the de-cell knock but it's a not-so-slow death for the engine.<br /><br />c/6<br />Hooty

 

[bJOHNSON]

Re: Weird noise from 90 hp

Gradual decell helped. I tried my OEM 17 pitch and my RPM was a light 5400 trimmed out. The installer had the motor set at the lowest setting. I raised it two holes and the RPM has not changed. I think this is where it should be according to other posts. I'm thinking of trying another prop. Any suggestions would be apreciated. I'm willing to go stainless if I have to. I did try a stainless about a month ago this was after I raised the engine. IT was a Solas 13.5 by 19. I got the same RPM as my OEM 14 by 19. Thanks alot for all the info so far you guys really have your poop in a group on this web site.