2 line vs 3 line fuel pump understanding.

[cenkaetaya]

1 - Fuel In
2 - Pulse Limiter Hose
3 - Fuel Out
4 - Back side of fuel pump crankshaft suction hole (not shown in photo)

Hi, I am trying to understand the difference in how these fuel pumps work along with the motor.

My first question is: I have a 1985's Evinrude and it has the bottom fuel pump with crank shaft hole but no Pulse port installed however, the engine does have a pulse port hole built in, but its closed off with a nut.

So would opening up the pulse port, adding a cable and using the Above fuel pump be better? would it make a difference?

Same with the 1995 motors, that have the pulse port hose, can you just cap the hose and use the Bottom fuel pump without issue?

Or is there a reason that using the Top fuel pump be be better?





Any help would be greatly appreciated.

Thanks

 

[flyingscott]

What motor.do.you have? Both pumps work the same way the only difference is where it gets it 's pulse from. The 2 cylinder motors have bosses and a pulse port in the block itself. So you just bolt it on and go. The later 3 cylinder motors do not have the pump mounting cast into the block. So that would use a 3 port pump because you would need a hose from a pulse port. When the VRO pump came around they started capping off the block mounted pump ports. This is because the Vro needs a pulse line. If your motor has the capped off pulse port and the threaded bosses you can use the 2 port pump. I believe some 3/ 4 cylinders had the ports in the block.

 

[cenkaetaya]

This is a 40HP two stroke evinrude.

So that is what im trying to understand, if i have a capped pulse port, or non capped one, is there any reason or advantage to using a 3 line vs 2 line?

Basically I have the same engine, 1 that used a vro, and an older one that uses a 2 line pump. This means I can use a 3 line or 2 line in each motor. So ... does it make a difference what I do? is 3 better then capping the pulse? and using a 2 line pump?

 

[flyingscott]

Use the port on the block that way you can mount it to something. Either pump will work just fine it is up to you.

 

[racerone]

Both pumps work the same way !-------A positive pressure pulse and a slight negative pulse.------I would mount the 2 line pump directly to the side of the block.----Plug the pulse port that was for the VRO pump.

 

[cenkaetaya]

So if i use the 3 Line pump, and connect both the pulse hose + block hole, it will work just as well as using the 2 Line pump, and plugging the pulse port?

Is there really no advantage to using the 3 line, with the pulse fitting instead of plugging it?

So what is the point of the 3 line pump? if you can just use a 2 line and plug the pulse hose?

Thanks

 

[flyingscott]

The 3 hose pump is for a motor that does not have the mounting bosses and pulse hole cast into the block. The 2 line pump can be bolted to the block over the pulse hose. Use either one makes no difference!

 

[cenkaetaya]

1 last question.

If I use the 3 line pump, do I still leave the block hole, open? so it has pulse + block home or, do I cap the block hole, and use just the pulse?

Thanks

 

[flyingscott]

No you do not use the block hole you must plug it.

 

[cenkaetaya]

Thanks, is there a reason the 3 line pump has the block hole on the back then? same as the 2 line? If i just have to plug it anyways.

Just trying to understand everything about how it works.

 

[flyingscott]

Its a vent. If you use the 3 line pump you need to remove the pulse limiter or drill it out.

 

[racerone]

Cenkae------You are overthinking this !--------The 2 pumps work exactly the same.------The difference is the way the pump body is drilled to get the pulses to the diaphragm.------The 2 hose pump mounts directly to the intake manifold and the pulse port.------The 3 hose pump uses a remote pulse source via a hose.-----Both pump the same amount of fuel !