I have messed à lot with my 1988 Xj 600’s carburetors since i bought it last summer, though it would not run får morse than a short while before the plugs were blackend with soot, leading to spitting/coffing and would ran only on 2 or 3 cylinders.
I cleaned them, adjust float levers,syncronized them and adjust the air screws and bought new plugs.
But still the same problem.
So i adjust the throttle needle levels to its lowest(leanest) position with the result that 3 cylinder stoppet sooting.
The still sooting on cyl 2 showed to be a damaged o ring in the carburettors air screw.
After changing all of the carburettors air screws o rings , it ran on all 4, but hesitated in midrange rpm.
I also sent down a step in heatrange on the sparkplugs from NGK dr8 es- L to 7, out of recomendation from a skilled mc mecanic and former racing driver, though he Said that the 8 es-L could be to cold of one drive mostly calm.
So i adjust the throttle needles 2 steps from the lowest lewels, to give it more fuel in the midrange register, thinking that should so it.
But now its sooting on all 4 sparkplugs again, and stop working on one or two cylinders again.
So i Will adjust the needles up one step, to see of it stops sooting and works in the midrange register.
But can this Yamaha Xj be so sensitive out of the reasons i mentioned, or can it be something else spooking?