dumb question about a fuel pump conversion

[mark in new jersey]

Hopefully this is an easy question....

I've read this:

http://forums.iboats.com/showthread.php?t=205628

And I'm thinking that this is a worthwhile conversion for my old 15HP Evinrude that I'm restoring.

Here's what I'm not grasping: What powers the pump?

 

[wilde1j]

Re: dumb question about a fuel pump conversion

Manifold vacuum.

 

[Sea18Horse]

Re: dumb question about a fuel pump conversion

Just to expand on what wilde1j said, it's the alternating pulses of vacuum and pressure in the crankcase or cross-over passages that powers the pump.

Cheers...................Todd

 

[mark in new jersey]

Re: dumb question about a fuel pump conversion

OK...I'm getting it...thanks!

I've been reading all I can and it seems that there's 2 ways to do it.....do I have this right?

1.) the "real conversion kits" (c. 1960) consisted of a pump mounted to (and plumbed through) a modified bypass cover. The pump drew it's pressure/vacuum from the chamber under the bypass cover.

2.) These days, lacking a "real conversion kit" you mount the pump somewhere and modify the intake manifold & fingerplate so that it isn't "just pressure" but pressure/vacuum. This requires closing off the channels to one of the crankcases & removing checkvalves, etc.

Pretty complicated, all things considered.

So here's what I'm thinking: why not simply mount the pump somewhere, drill & tap the existing bypass cover, thread in a 1/8" NPT nipple & power the pump that way? Sure sounds a heck of a lot easier......

Then I just need to cap off the pressure port on the intake manifold.

Is there some reason why that wouldn't work? Since I can buy bypass covers (on eBay), there's no real risk to doing any permanent damage of any sort.

So is there any reason why this wouldn't work?

 

[Daviet]

Re: dumb question about a fuel pump conversion

Give it a try and see how it works, sounds like it should work, keep us informed.

 

[freddyray21]

Re: dumb question about a fuel pump conversion

OK...I'm getting it...thanks!

I've been reading all I can and it seems that there's 2 ways to do it.....do I have this right?

1.) the "real conversion kits" (c. 1960) consisted of a pump mounted to (and plumbed through) a modified bypass cover. The pump drew it's pressure/vacuum from the chamber under the bypass cover.

2.) These days, lacking a "real conversion kit" you mount the pump somewhere and modify the intake manifold & fingerplate so that it isn't "just pressure" but pressure/vacuum. This requires closing off the channels to one of the crankcases & removing checkvalves, etc.

Pretty complicated, all things considered.

So here's what I'm thinking: why not simply mount the pump somewhere, drill & tap the existing bypass cover, thread in a 1/8" NPT nipple & power the pump that way? Sure sounds a heck of a lot easier......

Then I just need to cap off the pressure port on the intake manifold.

Is there some reason why that wouldn't work? Since I can buy bypass covers (on eBay), there's no real risk to doing any permanent damage of any sort.

So is there any reason why this wouldn't work?

I do them this way all the time. will work very well on an aftermarket pump. An OEM pump is made to mount flush so if you can get a bypass cover off an 18 hp later model then no need to use aftermarket, but I like this pump best. Works very well.

http://www.aircraftspruce.com/catalog/eppages/mikunifuelpump1.php

 

[freddyray21]

Re: dumb question about a fuel pump conversion

Manifold vacuum.

it's actually a pulse not vacuum

 

[kfa4303]

Re: dumb question about a fuel pump conversion

HI mark. You're right about the two methods, but it's not as hard as it seems. Check out this vid. It shows both ways. The best part about the 2nd method you mentioned is that you can buy an aftermarket fuel pump for a small engine of similar horse power made by companies like Briggs and Stratton for about $20 rather than the $40-$60 for an OMC factory pump. The first vid shows both methods, the second shows you the method you came up with any of them will work. Hope this helps. Keep us posted. Good luck.


http://www.youtube.com/watch?v=FtG4M7ye1N8&feature=related
http://www.youtube.com/watch?v=Suuy-827T78&feature=related
http://www.sschapterpsa.com/ramblings/Converting_dual_fuel_line.htm

 

[mark in new jersey]

Re: dumb question about a fuel pump conversion

I think I'm a happy guy!

I found a set of used Evinrude bypass covers that a.) fit my engine and b.) are OEM factory-designed to accept a fuel pump! One cover has the hose barb (and through-hole for air operation of the pump) and the other has threaded bosses for the mounting of the pump!

I know people complain about eBay all the time, but I gotta tell ya: sure makes it easy to find stuff that I'd otherwise NEVER be able to locate.

Oh, and a huge "thank you" to OMC / Johnson / Evinrude for using the same parts over & over & over on many different models for years & years!

 

[mark in new jersey]

Re: dumb question about a fuel pump conversion

I guess I'm confused still on which fuel pump to buy....

As stated previously, I found a pair of bypass covers that are intended for use with a fuel pump. It looks as if one cover provides the vacuum pulses (there's a barb on it with a through-hole)

Some fuel pumps have 3 barbs: fuel in, fuel out, vacuum. Like this. Simple to understand

But many others appear to have just 2 barbs. Like this one. How does that work?

Additionally, it looks as if the other bypass cover has extra mounting bosses on it....as if the pump actually mounts to it. (Or maybe I have no idea what I'm talking about.)

Can anyone steer me in the right direction? Is there a Sierra pump that's made to mount on these bypass covers?

 

[Daviet]

Re: dumb question about a fuel pump conversion

^^^^^ ???

 

[mark in new jersey]

Re: dumb question about a fuel pump conversion

sorry....you responded to an accidental posting on my part. The real message is above

 

[Daviet]

Re: dumb question about a fuel pump conversion

A 3 barb pump uses a hose to get the pulse from the engine to the pump, they can be mounted anywhere on the engine and just run a hose from the engine to the pump. A pump with 2 barbs is made to mount directly to the engine by using 2 screws and a gasket, usually on the bypass cover. You can use either one on your conversion.

 

[Scottri123]

Re: dumb question about a fuel pump conversion

What is the vacuum/pulse supposed to read on a vacuum gauge, mine goes from -2psi to 2psi But I dont seem to ever get it to pump fuel. I have treied this on two motors with three different pumps. What am I doing wrong. The pump is mounted exactly as described on the top cover. Thanks

 

[freddyray21]

Re: dumb question about a fuel pump conversion

it is a pulse not a vacuum so -2 to + 2 is about right. If you are using a barb off the bypass to the pump the line going to the pump cannot be too long as it's not much of a pulse. a picture will help us

 

[Scottri123]

Re: dumb question about a fuel pump conversion

I do not have a photo it looks just like the one in directions, THe pump is mounted right to the Engine, I used a gasket, tapped the holes and the center hole is drilled out. The lines are not on backwards. If I pump the ball I get fuel to flow through the pump but the engine does not pump any on its own. Did I just get 3 bad pumps? 2 where used off another running engine and one was new from napa. I even tried sizeing to a larger 50hp pump, and I have tried a 15 hp pump, the outcome is always the same. Both late 50's 35hp engines I have tried this on have about 2punds vacuum/pressure. 4psi swing. What am I doing wrong any thoughts?