mercruiser 5.7 crate motor 12 yr old

[jwkoehn]

carbed version motor runs great @ 3/4 throttle after 10- 20 sec at wot engine pulls back 300-500 rpm has new fuel filter I suspect a weak electric fuel pump. Before I do a fuel pressure test I thought I would get a couple of other opinions

 

[Scott Danforth]

you mean your motor drops RPM after a bit of time at WOT?

first place to check is fuel pressure.

could be plugged Anti-Siphon valve
could be plugged fuel vent

depending on electric or mechanical pump........ or carb vs EFI vs MPI.......there are a few other things to look for. however first is fuel pressure

 

[jwkoehn]

fuel pres gauge shows aprox 7-8 lbs would this cause a drop of 300-500 rpm @ wot pressure checked at carb inlet fitting

 

[Rick Stephens]

7 pounds is correct. Should maintain that all the time. So next is to see if you have 7 pounds when the motor starts bogging.

You can do a test run with a hook up of an outboard fuel tank direct to the fuel pump to see if the problem is fuel delivery from the fuel tank.