40 HP Losing 2 Cylinders

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selfel

Cadet
Joined
Jan 17, 2005
Messages
22
My 1986 Yamaha 40 3 cylinder started acting up this week. Runs like a top when for first hour of so on the water then intermittently loses both bottom cylinders at idle. If I let it idle for a while they will pick back up again, may run fine for a while then starts acting up again. It runs great at WOT, this just happens when it's idling. I've got good compression on all three cylinders and I don't think it's fuel related because when it's acting up I can pull the plug wires off the bottom two cylinders with no effect on how the motor runs. Any help would be appreciated.
 
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Ray Neudecker

Lieutenant Commander
Joined
May 25, 2004
Messages
1,656
Re: 40 HP Losing 2 Cylinders

Even though it sounds like a fuel restriction problem, I would also check fire first. Some of the three cylinders would intermittently have CDI failures.
 
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selfel

Cadet
Joined
Jan 17, 2005
Messages
22
Re: 40 HP Losing 2 Cylinders

Ray, thanks for the response. I've confirmed an electrical problem. When the motor "acts up" there is no fire on the bottom two cylinders at idle. When I rev the motor up high with the warm up lever both start firing again. Now I need to figure out if it's the CDI or some of the components under the flywheel.
 
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