Sound that occurs when in neutral

[acdc96]

Well on all my two stroke motors (including outboards, scooter, motorcycle, etc.) when in rev the engine in neutral their is this weird knock that resonates from the block when the rpms are winding down. I never have over reved my engines keeping them well below the max rpms. But I hear this on other peoples motors.
I'm not concerned at all. I keep my motors properly lubricated and clean.

Anyone else here this knock sound?
Anyone know why it occurs?

 

[Bob_VT]

Re: Sound that occurs when in neutral

Consider this food for thought

A 2 stroke lubricates from the oil in the gas..... the bearings and cylinder walls. When people rev up a motor more gas/oil is flowing and protecting the motor........ revving it up in N (bad practice) because there is no load and when the throttle is released the piston is moving w/o the extra lubrication for the rpms. Kind of an amplified clanging noise similar to piston slap.

 

[acdc96]

Re: Sound that occurs when in neutral

Ok
I only rev it in neutral when I'm trying to start it. Pull start no electric

 

[scipper77]

Re: Sound that occurs when in neutral

Very good food for thought. My 30 HP johnson is a pull start and it takes off when started in the start position. I guess I too am guilty of over revving in neutral.

 

[boobie]

Re: Sound that occurs when in neutral

It's just the clearances in the motor catching up with them selves when there's no load on the motor.

 

[Frank Acampora]

Re: Sound that occurs when in neutral

When you rev up in neutral then abruptly close the throttle, the fuel flow decreases and the engine four cycles--that is fires every other revolution rather than each revolution. That is the weird noise you hear. You can do it at home with your Briggs and Stratton lawn mower engine . The only difference is that already being a four cycle engine, raw gas is expelled into the exhaust and the engine will backfire repeatedly.

 

[acdc96]

Re: Sound that occurs when in neutral

When you rev up in neutral then abruptly close the throttle, the fuel flow decreases and the engine four cycles--that is fires every other revolution rather than each revolution. That is the weird noise you hear. You can do it at home with your Briggs and Stratton lawn mower engine . The only difference is that already being a four cycle engine, raw gas is expelled into the exhaust and the engine will backfire repeatedly.

I'm talking about 2-strokes not 4-strokes.

 

[Frank Acampora]

Re: Sound that occurs when in neutral

Re-read the answer. I am talking about two stroke outboard engines (Instead of firing every stroke--two cycle--they fire every other stroke--known as four cycling.) and simply using the Briggs as a 4 stroke example, showing that it is a common occurrence too! All small engines will do this. In fact, you can also get model airplane two cycle engines to "four cycle."