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Author Topic:   Johnson V4 Knocking?
Maximus posted 08-04-2001 12:21 AM ET (US)   Profile for Maximus   Send Email to Maximus  

Three weeks ago I changed the spark plugs in my 1996 90 HP Johnson. Since then I have noticed a subtle one-per-rev on engine decels. Almost like valves knocking on an overhad cam car engine.

My initial assesment is a loose, or several loose spark plugs - insufficient torque causing a air leak. The noise caused by high engine vacuum at decels. This will be checked shortly.

Other concerns are the VRO system is going south and I am hearing a mechanical bearing noise.

I have had no other problems with the motor and have put ~20 hours on it since changing the plugs. Starting, idle, power, and speed all seem to be normal.

Does anyone have any insight.

'67 Montauk

Clark Roberts posted 08-04-2001 11:10 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Max, can't diagnose long distance but if you suspect VRO (even slightly!) add oil to your gas immediately! Check that level in the vro tank goes down appropriately before you quit adding oil to gas... too much liability to NOT do this..!!! Check all other avenues as you describe and run a compression check, inspect plugs for traces of metal etc... hope it's just a hearing problem.. heh, heh.. Happy Whalin'.. Clark.. Spruce Creek Navy
Bigshot posted 08-04-2001 02:57 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Most engines will make a knock sound when you pull the throttle back to idle from a high speed.
Maximus posted 08-04-2001 05:21 PM ET (US)     Profile for Maximus  Send Email to Maximus     
Thanks for the comments. I regularly check my oil level and yes usage seems normal. I also see blue smoke on startups, so I am not all that worried about the VRO system. Believe me, mixing would have already been done :)

Again, let me re-iterate the fact that I have no other operability issues with the engine. Just a knocking sound on fast decels from above 4000 RPM.

Bigshot posted 08-06-2001 10:58 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My 225 does that. I think it is more of reeds than knocking. Could be though being no oil/gas.

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