Weird knokking sound when revving down...Help

[stingraymax]

Hello,<br /><br />MY 1999 JOHNSON 90HP is making a weird knokking noise when I rev down from over the 3000Rpm.<br />When I go to 2000Rpm and throttle down the noise isn't there. Only when i go over the 3000 and throtle down the I can hear the noise.<br /><br />Does anybody know what this could be ??<br />The engine runs fine and there is no weird noise when going at steady rpm...<br /><br />The engine is just out of the shop where they replaced 1 piston and all the piston rings on the other pistons, also the upper bearing was replaced and all new gaskets...<br /><br />I use 98ron fuel and quicksilver TCW3 oil<br />.<br />Also when I start the engine the pee stream is steady but not very powerfull after 2 seconds it is at full strength...<br /><br />any help please....

 

[andys15]

Re: Weird knokking sound when revving down...Help

The pee stream sounds normal. Just needs to get primed.<br /><br />The knock sounds like detonation. The timing may be a little fast or the mixture a little lean. You figure when you cut the throttle you're starving it of fuel (lean) at high speed, so it may knock. It's never good to do anything abruptly, does it kncok when you decrease throttle slowly?<br /><br />Also, how's the head temp? I think that may cause it to knock too. Any or a combo of the three or four I listed would probably cause that knock.

 

[Blueclaw]

Re: Weird knokking sound when revving down...Help

It's not the prop ratcheting is it? sometimes when backing down the clutchdog will make a clacking noise like a ratchet wrench does.<br /><br />Put you motor in gear with the motor off and turn the prop quickly in the opposite direction. Does it sound like that only faster?

 

[stingraymax]

Re: Weird knokking sound when revving down...Help

Thanks for the info. I will check the prop tomorrow.<br /><br />I was hoping it had something to do with the timing because the engine is harder to start after the rebuild and it idles at 1000rpm.<br /><br />before the rebuild after one turn of the key it started right up and would idle between 800 and 1000rpm.<br /><br />I never had a temperature alarm going of so i think the temp is ok ?.

 

[R.Johnson]

Re: Weird knokking sound when revving down...Help

On your engine, you are hearing a deceleration knock. Hit the primer, and see if the knock goes away. If it does, don't worry about it. Although! on a rebuild, that engine should run as good as it ever did. Are you using the proper start-up procedure, and can you drop the idle back down where it belong's?

 

[stingraymax]

Re: Weird knokking sound when revving down...Help

The start up what I do is.<br /><br />pump the fuel ball about 2 to 3 times until it is hard then I just turn the key wait untill i hear the signal and see all the lights go out.<br />Then I press the key in and turn it over until it starts.<br />If it lasts longer than 4 cranks untill it starts I wait 2 seconds and try again...