rpms down from 5500 to 4500

[rricci]

Currently have twin 2001 250 hp 0x66 outboards. First replaced all fuel filters since its happening in both motors at the same time. Next took off fuel injection pumps and the screens were pristine so did not go further and check screens in fuel injectors since the racor 10 micron fuel filters seem to be doing there job. Then tried independent fuel supply ran each motor off of a seperate 6 gal tank just to make sure fuel lines and pickups in gas tanks on the boat can be ruled out. Now is the next step the o2 sensors clean and or replace or fuel pump pressure under load test. What I don't know is there any type of synchro compensation involved i.e. if one engine only revs to 4500 it stops the other one from revving higher just as a safety device I don't know what to try next I have honestly tried to solve it on my own but as you can see I need help to proceed any info would really be appreciated. I don't want to run them lean and overheat and i then have two blown heads. Thank You again for your time.

[jb123]

there is no syncro between motors
go ahead with the running pressure test
O2s will USUAlly case a varying rpm
check low pressure pumps

do the motors run GOOD @ 4500 ??

u sure nothing has changed on the hull ,excess water,weight,barnacles?

[rricci]

they run great at 4500 rpms
no change in hull
no barnacles keep boat on a lift on side of house
will try fuel press test and o2 sensors next should i dissasemble and inspect fuel pump rubber diaphragms first.

[Tucker]

Wohh, both engines at the same time! coinsidence? If you run ring free I doubt it could be the 02 sensors but if they've never been cleaned it can't hurt to take a peek. Before I buy the gasket kit I would mix 2X5-gal cans of fuel with 10-oz of Seafoam in each and run 'em hard. If no improvement I think you can rule out carbon build up.

I'll be following this one. I haven't read about this problem happening the same time with both motors. Let's keep this thread at the top. Need some heavy weight techs to chim in on this, how 'bout it guys?