1996 Evinrude V4 90hp Engine Surge Issues

[Great Wakes Services]

I have a customer with a 90hp V4 with VRO pump setup. The engine begins surging/loss of power at around 3000rpm. I have eliminated several things and I think I have it narrowed down to either the fuel pump or the carbs. When I tested fuel pressure between the pump and carbs it was reading 2psi-10psi. The gauge would drop from 10psi slowly down to 2psi over about 2-3seconds then bounce back to 10psi very rapidly. This seems to indicate an issue with the fuel pump as the service manual says it should never drop below 3psi. I am not sure if the wide range of pressure is normal on these pumps. I am not sure and the part is $600 so just throwing a part at it is not really an option. Any ideas on where to go from here?

Things I have eliminated:
CDI
Temperature Sensors
Fuel supply to the fuel pump
Spark Plugs
Fuel Filter

 

[boobie]

Have you tried pumping the primer bulb when the motor starts to surge ??

 

[oldboat1]

Welcome Wakes -- like the handle!

Agree with Boobie. On a regular non-VRO pump, the diaphragm would be suspect. Maybe the same issue with the '96 VRO (think kits are available -- $150 or so?)

 

[Great Wakes Services]

I tried pumping the bulb when I first started to diagnose the issue and it did improve but I have this boat on the lake several times since then and pumping the bulb no longer makes the issue disappear.

 

[Bosunsmate]

Is the primer bulb holding firm with engine off? Ive had surging caused from carb floats becoming dead over years from fuel contamination etc