Too much gas

[Shawn]

I have a 1992 SPX with the 580 motor, Mikuni
BN38 single carb & everything else stock. It
seems to idle fine & from fully closed to 1/4
throttle appears to be on par. Throttle openings from 1/4 to WOT cause the engine to
run rough (seems like it is getting way too much gas on high speed circuit). Setting high
speed screw to fully closed position has no effect. On the trailer it smokes a lot (black
sooty from over rich condition) when above
1/4 throttle. What are the starting values of
slow speed jet, main jet, needle & seat size,
pop off spring type for use at sea level at
Northeast Florida during summer. I want to
jet this ski right. BTW, compression reads about 155 or so at each cylinder & both
plugs are a dark brown & not oil or fuel
fouled.

Thanks

[Bryan Glynn]

You have an SP, not an SPX.

The low screw should start at 1 1/4 turn.

I would check your needle and seat, it may be leaking and need replacement.