VST Pump..2 Shutter? or 4 Shutter?

[atcoast2000]

My High Pressure fuel pump went out on my 1997 merc 250 CXL EFI..my part number for the VST is 825818A13 and it says it is a 4 shutter. I know where there is one for sale but the part number is 825818A12 and it is a 2 shutter and it came off a 1996 225 EFI...What are the shutters they are talking about ? what is a shutter ? the person that has it for sale says that it will work on my engine and he says the part numbers cross. But im not so sure. It will probably work but it is not the same thing. So what are they referring to when they talk about shutters?

 

[Faztbullet]

Re: VST Pump..2 Shutter? or 4 Shutter?

Pumps are the same, just a revision thus the A13 number... 2 and 4 shutter is the refer to throttle plate/air management system.