Uneven RPMs, Black Exhaust

[Dr. Pill]

Just splashed our 2001 SR 310 Friday and did a shakedown cruise yesterday. The motors (Horizon MPI 5.7 IB) ran fine and performed as expected except there was a difference of 300-400rpm between the motors while the throttles and synch indicator guage were even. Also, the port motor put out an unusual amount of black smoke through the exhaust initially but seemed to stop after a few minutes. I know this may not sound serious, but the rpms. synch guage and throttles have for the past 4 seasons have always been right on. The one time they were off was 2 seasons ago when I had water intrusion in the port motor.
Any ideas?
Thanks,
Dr. Pill (formally Mainiac)
South Portland, ME

 

[PlayDate]

Just splashed our 2001 SR 310 Friday and did a shakedown cruise yesterday. The motors (Horizon MPI 5.7 IB) ran fine and performed as expected except there was a difference of 300-400rpm between the motors while the throttles and synch indicator guage were even. Also, the port motor put out an unusual amount of black smoke through the exhaust initially but seemed to stop after a few minutes. I know this may not sound serious, but the rpms. synch guage and throttles have for the past 4 seasons have always been right on. The one time they were off was 2 seasons ago when I had water intrusion in the port motor.
Any ideas?
Thanks,
Dr. Pill (formally Mainiac)
South Portland, ME

In regards to the black smoke, it might be worthwhile to replace the spark plugs and see what they tell you. You didn't mention how many hours were on the engines or any damage that resulted from the water intrusion.

In regards to the engine sync/throttle postions/engine rpm.....is the engine sync reading center and the tachs are off by 300+ rpm? Or is it the case where when you even the throttles, the engine sync and tachs are off? In the case of the former, your tach(s) might be the problem. In the case of the later, your throttle cable(s) may have slipped.

-John