96 yamaha 40 HP 3 cylinder air box fooding with fuel

[roscoman]

My outboard has a misfire/backfire problem. It has a random misfire/backfire which almost stalls the engine and sometimes does. I have done a compression test. All cylinders measure 90psi. Had the flywheel off, there is no blow past the crank seal. Had the carb's off and cleaned and checked. Seem ok. Never put new kits in though. Have set the air mixture scews to one and a half turns out. The bottom spark plug seems to wash cleaner than the other two. I have also noticed that I have a lot of fuel catching in the air box.

I advanced the timing setting on the CDI box and this has smoothed out the problem, but it is still there just not nearly as bad. This is not the correct fix I know and I would like to sort the problem properly! Any help would be greatly appreciated, Thanks.

 

[99yam40]

Re: 96 yamaha 40 HP 3 cylinder air box fooding with fuel

it kind of sounds like a lean sneeze.
Check your fuel pump for hole in diaphragm, but that will usually cause the bottom cylinder to run too rich not lean.
Check timing with a timing light and make sure it is set like the manual says, too far advanced can hurt the motor.
If compression, spark, and timing are good the you may need to do the carbs again, and make sure to do the link and sync like the manual says after putting carbs back on

 

[ertlj]

Re: 96 yamaha 40 HP 3 cylinder air box fooding with fuel

dont forget the enrichner vavle diaphram for a hole as this will flood engine

 

[roscoman]

Re: 96 yamaha 40 HP 3 cylinder air box fooding with fuel

Thanks for that. Sorry fogot to mention that I had checked the timing and synched the carbs as well. I think the next for me is to do a full carb kit. What does it entail to check the correct fuel delivery? Excuse my ignorance but where do I find the fuel enricher diaphram?

 

[ertlj]

Re: 96 yamaha 40 HP 3 cylinder air box fooding with fuel

the diaphram is either on the #2 or #3 carb also make sure your manual choke is off