2000 Merc 250 EFI rpm loss

Just purchased a used 260 Proline with a 250 EFI merc. Had a 100 hr service performed and also had new thermostats and poppet valvle replaced. Took boat out for shakedown Monday and ran fine at 4400rpm cruise 30-31 mph. Suddenly slowed to 3500 rpms. No alarms went off, oil tank full and temp at cruise 160-170deg. Shut off and cranked up again and it ran fine for approx 45 min to an hour went from 5000 rpm to 4000rpm. We ran the boat approx 4 1/2 hrs and it continued to be a problem. The shop that did the initial work is 3 1/2 hrs away so taking it back isn't an option.<br />Also appears to have a very noticeable vibration from 1600-1800 rpm. Lower unit had checked out Ok in shop.<br />Thanks for any help.<br />Ralph

Re: 2000 Merc 250 EFI rpm loss

Any help?

Re: 2000 Merc 250 EFI rpm loss

First let me say, I have little knowledge of these newer mercs. But i would strongly reccommend getting mercury factory manual and a Seloc manual for your engine. They will pay for themselves, they are great!! From my experience with V6 mercs from late 80's to early 90's. I would say a loss in RPM's could be many things. 1) your carbs are gummed up and need to be cleaned (a manual will make this a very easy job). <br />2.)The high speed coils in your stator are going bad.<br />3.)The switchboxes are damaged<br />4.)Fuel pump could be bummed, try pumping the primer bulb when you loose RPM's if you regain the RPM's its your fuel pump.<br />5.)Check for damage in your throttle linage.<br /><br />A manual will help you do all the tests necessary, with the aid of a mulitimeter and DVA adapter, to check your ignition system.<br /><br />Does it suddenly loose RPMs?<br />As far a the shaking... Merc's like to vibrate. But the timing could be a bit off or the fact that your carbs are dirty would certainly cause this.<br /><br />Get back to us with some more details.<br /><br />-andy

Re: 2000 Merc 250 EFI rpm loss

Almost forgot, this site should have the factory manual for your engine.<br /><br />www.biggerhammer.net/mercury/factory_manuals/<br /><br />good luck-<br />andy

Re: 2000 Merc 250 EFI rpm loss

rebuild the small square fuel pump on the motor. they dont live long. then remove the lower part of the vapor seperator tank and remove and clean or replace the VST filter. supposed to be done annually but it never is. if ya have a yam dealer close its the same VST pump and filter the early 225 yams used. the later yams used a slightly different VST gasket. you describe the classic symptoms of an EFI running out of fuel. that little square pump is the same for most all V6 mercs only on the 250 it has to move a lot of fuel. and if the vst filter is partially plugged it will cause bogging cause the injectors just cant get enough fuel.but all of the above should be on your annual maint schedule. the low pressure pump is not listed on the maint schedule but experience dictates they get weak and fail to provide adequate fuel to the vapor seperator.