Yamaha 250 SW II rpm drag

2000 Cobia 240 WA with 250 SWII Yamaha- I thought that I originally had a fuel issue. Would top out at 5100 RPM then drag back down to 4600. Change seperator, fuel filter, plugs and made no difference. Still ran fair, with less power, noticed that when I hit my power trim tabs, motor trim tilt, even spotlight (anything that draws a good shot of electricity that the RPMs momentarily ( a few seconds) jumped right back up to 5100 for full throttle. Now I am concerned that this is more of an electrical issue than a motor issue- any thoughts. With all of this, my Simrad autopilot has also started giving me fits and will not work correctly. I think that this is more than just coincidence.

I am handy, but this is not my cup of tea- any ideas where to start?

Thanks- Scott

Re: Yamaha 250 SW II rpm drag

could be a loose/corroded connection. check your ground wire.

Also, what's the maint history on the VST screen and low pressure pumps?

Re: Yamaha 250 SW II rpm drag

I have owned the boat for 3 years and have not had anything done other than regular maint (plugs, wintering, bottom), it has always been a good runner. Noticed today, that low idle is less smooth as in the past. If I run live well or bilge, anything with some draw, it still increases RPM's.

Thanks for the starting points.

Re: Yamaha 250 SW II rpm drag

most likely a fuel issue related to the VST screen. I would clean and replace.

Also, you are way overdue for some routine maint on that OX66 motor. I'm assuming it's fuel injected since you didn't post the full model number.

my preventative maint items include:
1) replace low pressure fuel pumps
2) replace/clean VST screen and o-ring.
3) clean pressure regulator screen on VST.
4) clean fuel injector screens
5) clean/test O2 sensor for proper output voltage.
6) replace water pump
7) replace engine filter and water separator filter.
8) inspect/clean out popit valve; PRV.
9) link and synch and set TPS.
10) replace thermostats.
11) check that resistance of spark plug caps are in spec.
12) properly adjust the oil linkage rod.
13) clean filter on remote oil tank.