Engine running rough

[<OutOfIdeas>]

I have twin 1997 yamaha 150 SWS motors, the port motor has recently started running rough, initially at 2000 RPM, now it is running rough at all ranges. I have changed park plugs and fuel filters, it shows no improvement. Is there anything I should check in addition, could this be electrical (magneto, coil)?
Thanks!!

[Hamfisted]

If you don't have one already go to www.Yamahapubs.com and order yourself a factory service manual for your motor. It will have troubleshooting guides and specs to test things like the coils, plug wires, fuelpumps...compression test. When you took the old plugs out did your notice if one looked different than the all the others? Without the service manual you're just shooting in the dark.


Mike ...... Miami, FL

[<bernieb>]

Change the low pressure fuel pumps if they haven't been changed for several years.Check fuel pressure at schrader valve.

[<OutOfIdeas>]

Thanks, I will try the fuel pumps

[<jb123>]

yes,be sure your fuel pumps have one direction flow,you can take them off and blow thru both ways...one way will flow the other should not let any pass....cheap enuf to change out tho. have you cleaned the carbs?? thats most of the time the culprit. tear them down as far as possible and soak overnight in a cleaning solution and replace any of the corroded washers.i use a can of spray for each and blow thru every opening,jet, orifice. sometimes it may take a couple/few times to get it right.
good luck

[<jb123>]

also check from pickup to motor, all hoses,pickup tube,clamps,water separators and junctions. i would replace all hoses/pump balls and have the least amount of junctions in the line as possible. any air leak ,faulty separator,cloggged screens in pickup will slow fuel flo and give you troubles.