2007 Mercury Pro Xs 225

[jnbboatrestorations]

Serial Number 1B519074

I have a 2007 mercury pro xs 225 has roughly 400 hrs on it been having issues for about the last 4 months. When running boat wants to start surging at high rpms like its starving for fuel. We have changed new fuel lines primer bulb from tank to the motor. Pulled vst cleaned and checked pumps are good. Have 100lbs of fuel pressure at fuel rail and 90lbs of air pressure. We have put it on computer everything electrical is working fine. Had injectors cleaned checked all the diaphragms everything is working order. Stumped on where to go next other than tieing a rope to it and using it as a boat anchor. Please any help would be greatly appreciated. Thanks

[paulrodbender]

https://www.bbcboards.net/forumdisplay.php?f=7

Post here for good help.....

[DaveBrabec]

Buddies was doing the same. His was the reeds

[Randrat]

^^^^^^ This.

[neverenuf]

Make absolutely certain your fuel line internal liner didn't get damaged/curled up while installing it on the primer bulb and other fittings. The internal liner will crunch up and reduce the ID of the hose. Mercury fuel line especially. It has to be soaked in hot water then installed. I hate Mercury fuel line. I had the same issues you are describing on my '07 225 Opti.

[DaveBrabec]

As far as I know the pro XS has carbon fiber reeds and reg Optimax has metal ones.

[jnbboatrestorations]

we have 100 psi at the fuel rail even when its acting stupid

[rocketmanjp]

A friend had the same yr & size motor several yrs ago & was having a similar issue for a long time they couldnt figure out. It ended up being a twisted cylinder sleeve which required a complete rebuild. I think the heads have to be removed to determine. I hope this isnt your issue but something to look for if they cant find anything else wrong.

[Murph McB]

Sounds similar. My problem ended up being an injector. I had to isolate to find the problem.

[jnbboatrestorations]

we have clean all injectors fuel rail and air injectors

[jnbboatrestorations]

Update changed air compressors today still doing same thing took apart mine and there was no damage inside looked pretty much brand new so gonna switch out vst tomorrow and see if that's the problem wish me luck

[Murph McB]

Have you narrowed it down to any particular cylinder?

[jnbboatrestorations]

update/////// had a torn o ring in the vst high pressure line boats running like a top now

[lpugh]

we have 100 psi at the fuel rail even when its acting stupid

Post in the 3.0 mercury forum for better help.
100 psi tells us nothing useful.
Need dual glycerin filled gauges, 1% accuracy, Must have air and fuel pressures at exact same while it is surging, also need low pressure reading off the port on the vst at same time, should cot fall off and should be at least 20 PSI
Slipping air compressor belt can cause this as well, check it and the tensioner spring by using a in lb torque wrench. Requires at least 70in lbs to rotate tensioner before it reaches the stop.
Fuel Pressure must be exactly 14.2 psi higher than air pressure 94-96 psi (648-662 kPa) air vs. 108-110 psi (745-758 kPa) fuel.