I have a 1999 - 200 hp Yamaha OX66 EFI outboard that idles rough at less than 1000 rpm's. The engine will often idle then die but starts right up again. Runs fine above 1000rpm's and top end is fine. The O2 sensor carbons up but I've cleaned it and I add fuel additives. The fuel bulb remains tight after squeezing so I don't think it is a pressure fuel leaking problem. I run Mercury Premium Plus oil and change the spark plugs each season. All the boat mechanics are way behind this time of year so I don't want to wait months for it to be repaired...any help from here would be greatly appreciated. Thanks Guys.

Sounds like either a fuel filter or fuel pump strainer screen clog. Do you have a water seporating filter.. i'd also check for water in the fuel filter bowl while you're at it.

I had a fuel pump strainer screen clog that did that to my Series II 200 HPDI.

I can take a look at it anytime and try to determine which cylinder it is and then go from there. Might have a leaking injector or clogged injector. www.BearMarine.com Pilot Point Texas

Thanks for the reply...as far as I can determine there is only one fuel filter and it is on the side. I have emptied it but not replaced the filter in it. I may try replacing the filter just in case I'm not seeing anything wrong with that filter. I've looked at the schematics but not sure where to find a "fuel pump strainer screen"...tell me where to look and I'll check that out. Thanks again for the help. I'll let you know if I find a solution.

Bearmarine...I live in Dumas, north of Amarillo but I'm coming to Dallas soon. If your offer is still there I'll contact you and bring the boat to you. Does the Ring Free, Seafoam and Stabill help unclog injectors? Anyway to tell if it is a leaking injector without diagnostic equipment?

Seafoam might. Check your fuel line for inner deterioration from ethanol too.