# Duel fuel line conversion.



## macawman (Mar 20, 2018)

I'm working on converting my 1956 Johnson 10hp from an old duel line/pressurized tank system to a single fuel pump system. The obvious solution is to replace an existing bypass cover with the plate and pump from a post-1962 model that was manufactured with a fuel pump. Unfortunately, it seems those parts are not to be found so I'm looking at other options. Particularly, those detailed in this article. https://www.leeroysramblings.com/Converting_dual_fuel_line.htm

One option is to fill the void in the existing bypass cover (picture below) with liquid steel to create a flat surface to mount a pump on.




The second option is to replace the existing bypass cover with a flat plate (picture below) on which the pump can be mounted.
This is the option I prefer but I'm concerned about the inset area of the existing cover not existing. This inset conforms to the curvature of the cylinder.




Would the lack of the inset on the flat plate effect engine performance or otherwise cause problems?


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## Shaugh (Mar 20, 2018)

I've done it on a plate that had a place where I could drill and tap a 1/8" barb fitting into... How thick is that plate ?

It's this method discussed on Leroy's page:

Another alternative using a Sierra # 18-7353 later fuel pump designed to be independently mounted where you would need to tap into one of the sideplates for a suction (vacuum) source. This would normally be using a 1/8" national Pipe Tap and a screw in barb with hose running to the the fuel pump wherever you can mount it, yet get the cowling cover to close.

You just need to mount the pump elsewhere on the motor and attach a hose to the fitting...


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## macawman (Mar 20, 2018)

Thanks for the response, Shaugh.

The plate is 1/8 inch thick steel. I am considering the option you mentioned, but was concerned about pressure/vacuum drop in a remote install of the pump. Did that cause you any issues?


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## Shaugh (Mar 20, 2018)

No it works fine. I’ll find some photos.


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## Shaugh (Mar 20, 2018)

I couldn't find any of my photos... I've done it on a 57 and a 58 18hp before... but those plates looked like the one in this thread:

https://www.marineengine.com/boat-forum/showthread.php?378391-Johnson-FD-12-18hp-1958-convert-2-single-line-fuel-sys

There was actually a hole already cast in the plate that you needed to simply drill through and tap.... that 56 10hp plate doesn't have that.. so being only 1/8 thick I'm not sure you can tap it enough to get a good seal and permanent attachment.... I'm sure I could figure out how to make it work.. maybe with thin nut on the inside.. but I'm not sure about how much clearance you have under that plate.

I don't like the idea of simply attaching a flat plate instead... It seems to me that they engineered those plates that way for a reason... might not be good to have them out of balance.... 

I'd consider tapping that plate and see how well it works with a 1/8" NPT brass nipple... you'll need to grind some off inside I'd guess... it might work fine......

Edit.. I checked further.. a replacement for that plate is easy to get and cheap.... I would try to tap it... if it doesn't work you can get a new one for 11 bucks:

https://www.marineengine.com/newparts/part_details.php?pnum=OMC0301848


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## macawman (Mar 20, 2018)

Completely agree with your concern about using just a flat plate. I saw some plates like the three pictures you posted, but I could not find one where the bolt pattern matched a 56 10 horse.

I thought about just drilling and tapping the original cover, but it is thin cast pot metal so I doubt it would hold a thread. The 1/8 inch thick steel plate is probably too thin for that as well.

What I am thinking now is to drill a 1/4 in hole in the original part and in the flat plate. I would then place a nut sized for the barb fitting over the hole in the outside of the flat plate and weld it in place. These parts would then be installed in the order of ...

Gasket/original cover/gasket/flat plate

This would retain the original cover with it's inset but convert the inset to a sealed chamber.

Thoughts?


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## Shaugh (Mar 20, 2018)

Yes that would work.. I didn't like the idea of a nut inside the motor cavity ... that can fall off and create disaster...

my best idea is that an NPT tapered brass nipple would eventually seal into that plate very securely... but it might come loose.... what about doing that... then grinding off the protrusion inside... and then taking it to be brazed on the outside ? I think a good welder could make that a very permanent joint... ?

I've searched pretty hard and those plates designed for the fuel pump simply don't exist anymore... so your options really are down to finding a way to use that existing plate.... it's aluminum.... I think it would braze to the brass....


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## macawman (Mar 20, 2018)

Thanks for the input, Shaugh. It's great to have experienced people to bounce these issues off of.


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## Shaugh (Mar 20, 2018)

https://www.youtube.com/watch?v=lGy7pHx6P3Y


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## Pappy (Mar 20, 2018)

Why do you want to convert to a single line? 
The dual line system is pretty much bulletproof. The diaphragm and valving are up above the gasoline when not in use vs a fuel pump. The pressure in the tank will not allow moisture through any kind of vent while running and the tank is steel so it will not expand and look like a huge orange football rolling around your boat. 
I much prefer pressure tanks on the old engines. For the immediate future all rebuild parts are still available to rebuild the old tanks as well.


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## macawman (Mar 20, 2018)

Hi, Pappy. To be totally candid, I guess you could call it "plain lazy". The entire fue delivery system from the carb inlet out is missing or non-functional and has to be replaced. I found the necessary parts and pieces on eBay for a two tube system, but with the exception of the flat plate that I made myself, I found all the parts needed for a single pipe installation at at least a dozen local sources for about the same cost.


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## Shaugh (Mar 21, 2018)

Note that if you do the hose barb and remote mounting of the fuel pump, you'll need this type... with the 3 fittings... Not the one with 2 fittings and the gasket commonly referenced.

https://www.ebay.com/itm/New-Fuel-Pump-Fits-Mikuni-491922-691034-692313-808492-808656-Briggs-Stratton/121437514737?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649


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## macawman (Mar 23, 2018)

I ordered the sienna 18-7353 remote mount fuel pump being aware the there where connections of different sizes(1/8, 1/4 and 3/8). I knew that two of the ports were fuel in and fuel out and the third one was vacuum. I did not know which is which. No big deal, the pump will come with documentation. WRONG! 

I'm assuming the 1/8" port is vacuum. Can someone tell me which is which of the other two?


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## Shaugh (Mar 23, 2018)

See the arrow on the black plastic fitting ?

I've never used that pump... the one's I've used had the vacuum line attached to the dome...see the link below.. that one doesn't.... but the arrow can't be wrong... that's gotta be fuel in...

https://www.ebay.com/itm/FUEL-PUMP-REPLACES-Briggs-Stratton-491922-808656-Kohler-24-393-16s-24-393-04s/182721228531?rt=nc&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D44039%26meid%3D8f04f6c318e74f50ab9f68b750dccb04%26pid%3D100005%26rk%3D4%26rkt%3D6%26mehot%3Dpp%26sd%3D121437514737%26itm%3D182721228531&_trksid=p2047675.c100005.m1851


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## macawman (Mar 23, 2018)

This is the pump I got. I see the arrow on the 3/8" plastic fitting on the top now so that probably is the fuel inlet port. I guess the remaining 1/4" port would be the fuel outlet. That would make sense given that the inlet of the carb is 1/4".


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## macawman (Mar 23, 2018)

Forgot to attach the photo.


Forgot to attach the photo.


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## Shaugh (Mar 23, 2018)

That’s gotta be right. Big pump. Did you find a place where it will fit under the hood?


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## macawman (Mar 23, 2018)

Yes, it is a big pump. Found a spot that works with the housing, but there are no mounting holes so I will need to fabricate a bracket for it.


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## Shaugh (Mar 23, 2018)

It’s ok to just zip tie it too.


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