lean sneeze 200 HP premix tech questions

[diveguana]

I have a 200HP premix 2004 ( in the Bahamas ) so serial #s would not apply.

My question is in reference to a lean sneeze. The engine developed a sneeze at idle . Sometimes it would sneeze and keep running and sometimes it would sneeze and shut off. Fires right back up but a pain when docking.

I rebuilt the carbs. changed gaskets, reset float heights, synced throttle valves and set the screws out 1 1/8 as per manual . it improved but still sneezes occasionaly.

DO I adjust in or out on the screws to give more fuel . Do i turn all the screws out equally ? How do I know which are running lean and which are running rich ?? Am I correct the the stbd side of the carb feeds the port cylinder on that level ??

Thanks for any insight . It is driving me crazy

Thanks

Troy

 

[rodbolt]

Re: lean sneeze 200 HP premix tech questions

on those carbs the A/F mixture is controle by the pilot fuel jet, in the fuel bowl, and the pilot air jet, in the upper part of the carb airhorn.
the mixture screws simply allow more or less of it through but does not change the air to fuel ratio, thats controled by the above mention jets.
my guess is one or more of the pilot fuel jets is clogged or vrnished.
occasionally I hve to play with the pilot air jetting, open it up and it idles leaner, make the hole smaller and the idle mix gets richer.
I do more jonnyrudes than ymahas this way but occasionally I have to play with all of them.
if everything is correct the factory yamaha settings work very well.
you may also wish to test the recirc check valves that are pressed in the block.

 

[diveguana]

Re: lean sneeze 200 HP premix tech questions

Thanks
But how do you know which cylinder is running rich ( or lean ) ?

 

[diveguana]

Re: lean sneeze 200 HP premix tech questions

How do I test the recirc valves ??