Yamaha outboard shuddering

[Rum_Pirate]

I have two 85hp 2-stroke Yamaha outboards.

One 'shudders' from time to time, then seems to 'clear' the problem' - reduce throttle/turn off and restart and - then runs OK.

Both linked to the same fuel tank.

Any suggestions as to the cause.

 

[longjohnsilver]

Blocked jet(s), faulty spark plug?

 

[Kawasaki]

Yep LJ, that’s where I’d start

 

[VicS]

I have two 85hp 2-stroke Yamaha outboards.

One 'shudders' from time to time, then seems to 'clear' the problem' - reduce throttle/turn off and restart and - then runs OK.

Both linked to the same fuel tank.

Any suggestions as to the cause.

Dropping one cylinder ??

As suggested spark plugs are first check......... could try swapping them with the plugs in the other engine.

Ht leads ??? Coils ?? Defective CDI possible

Info on diagnostic testing in the CDI Electronics Troubleshooting Guide http://www.cdielectronics.com/troubleshootingguide/

 

[Rum_Pirate]

Blocked jet(s), faulty spark plug?

Thanks.

I have changed and re-gapped the spark plugs.

I will remove and clean the carbs(jets).

When shutting down I disconnect the fuel line and let the engine use up the fuel in the line.
However this probably does not empty the carbs or jets.

 

[Rum_Pirate]

Dropping one cylinder ??

As suggested spark plugs are first check......... could try swapping them with the plugs in the other engine.

Ht leads ??? Coils ?? Defective CDI possible

Info on diagnostic testing in the CDI Electronics Troubleshooting Guide http://www.cdielectronics.com/troubleshootingguide/

Appreciated. will follow up. :encouragement:

 

[AndieMac]

......When shutting down I disconnect the fuel line and let the engine use up the fuel in the line.
However this probably does not empty the carbs or jets.

The procedure (running engine until it stops) you are following is what is recommended to eliminate residual oil blocking jets and gumming up carb bowls. I always do this with any two stroke on shut down also.