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 !

 

[mayfieldkm]

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.

Came here for this same question because I'm replacing my fuel pump and it showed up at my house and has an extra outlet. Is it OK to just use the little black cap that it shipped with to plug the vacuum port (like #2 in the photo). Maybe just add a small hose clamp around it to secure it and prevent air leaks? Mine mounts to the block and the pump has the vacuum port on the back of it. I premix, no VRO.