Topic: 1965 40 Johnson Fuel Pump – Antique Outboard Motor Club,Inc

This topic has 8 replies, 5 voices, and was last updated 7 years, 9 months ago by jerry-ahrens.

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July 24, 2016 at 3:13 pm #4829
jerry-ahrens
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The original fuel pump for this motor superceeds to a 388685 pump. It’s the smaller square pump, with the multi directional inlet fitting. Will this pump run a 40 hp motor? My customer doesn’t want a rebuilt pump, but would rather have a new one because his kids will be using the boat. I wondered if anyone has tried this on a Big Twin 40? Thanks!
July 24, 2016 at 4:16 pm #40815
fleetwin
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I ran into the same thing on a 64 Bigtwin… I saw the small OMC fuel pump on this engine and just assumed it was the wrong pump, but then looked it up to see that this small pump is what the original one supercedes to now. I’m pretty sure I looked at the little pump and its orientation arrow or "up" was oriented correctly. The only thing I did do was to remove/bypass the engine’s original mesh filter because this replacement pump does have a screen filter, so the second filter seemed redundant and could cause fuel flow headaches.
July 24, 2016 at 4:28 pm #40816
dan-in-tn
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Depending on the application (space limitations) I find that the larger pumps work much better with today’s fuels. Don remember the vapor lock issues OMC ran into with the 9.9/15s? They went to the large pump to cure that. I think the large pump for the Big Twin would be #438562. Notice it mounts for the vaccum port and has the small outlet nipple. There use to be a pump you could order that came with multiple size outlet nipples? The nipples just screw in with an oring for the seal. The large pump is actually cheaper & a much better pump. Easier to rebuild to boot if need be in the future! Just my opinion!

Dan in TN
July 24, 2016 at 8:14 pm #40834
chris-p
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I agree with Dan, go with the bigger pump. there is room for it in there.
July 24, 2016 at 8:37 pm #40838
frankr
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Or Sierra 18-7351. Besides, it is..SO..much simpler. As they say, keep it simple.
July 24, 2016 at 9:44 pm #40843
jerry-ahrens
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I also thought the larger 2 nipple pump would be better, but I have a brand new 388685 pump [smaller one] on the shelf, so thought I could use it. The parts book saye’s it’s the correct replacement, but I wonder how they want the average do it yourselfer to deal with the smaller size barbs? The fuel line [carb to pump] will need to be adapted down to fit this new pump. Kinda seems funny to me that there’s no mention of this when installing on an older Big twin.
July 24, 2016 at 11:27 pm #40851
chris-p
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One of the reasons I like the larger pump! You can get the larger inlet barb, for section between tank connection and pump, then the smaller barb for length between pump and carb. Works perfectly.
July 24, 2016 at 11:29 pm #40852
chris-p
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When I did one with the small square pump, I used 3/16" line. Fits the pump perfectly. To get it over the barb on the tank line connection, you have to warm it up good with a heat gun, to get it over the barb, but is do able.
July 26, 2016 at 4:16 pm #40978
jerry-ahrens
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I’ve got one of the larger pumps on the way, so I think I’ll go with that option. Thanks for all of the reply’s.
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1965 40 Johnson Fuel Pump

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