1999 Ox66 excessive fuel use

[patmqueen]

Yamaha OX66 V250 Saltwater Series Model L250TXRW 618 X

Have a twin OX66's. After launching this season I have noticed that the port engine is using significantly more fuel than the starboard engine. Depending on RPMs it is using 1.5x to 2x the fuel. At first I assumed it was a bad fuel monitor but the port tank is much lower as well. (clearly using more fuel)

On the last trip when I ran much faster than my typical cruise the port engine lost power mid cruise. At 32-35k RPM all is great. But when I stepped up to 41k RPM the boat would run for a while but then stumble. (loose power ...) When I pull back the throttle it idles fine. And with throttle the boat seems fine and gets back up plane. The Port engine will not reach WOT any more either ...

I had a Yamaha certified mechanic take a look - And other than new plugs they did not see a thing wrong. The fuel pressure looked fine. Unfortunately there are not many Yamaha mechanics near the boat. I was really disappointed as the Yamaha mechanic did not test the O2 sensor. The fuel burn and stumble is happening every time we go out and there is clearly something wrong. Any ideas on how I can troubleshoot?

Thanks!

Pat

[99yam40]

The W says it is a 1998 not a 1999.

When was the last time you replaced the lift pumps?

Did they monitor the fuel pressures when problem showed up?

[patmqueen]

Hull is 1999 - Engines could easily have been made in 1998.

I have only owned the boat for five years - and have not replaced the "lift pumps" is that the same as the low pressure fuel pumps? When the mechanic went for a ride he did test the fuel pressure at the schrader value and pronounced it "good." I don't have the numbers.

Pat