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Mechanical vs. Electric fuel pump
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malcolm2
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PostPosted: Fri Nov 15, 2019 7:42 am    Post subject: Mechanical vs. Electric fuel pump Reply with quote

Here is the deal. I have a 1.8L out of a 914. I have opened it up and I am inspecting everything. The PO told me it was running. Everything looks really good so far. Only tiny thing I found so far is it looks like one of the crank bearings spun about a 1/4" and the dowel pin dug into the bearing. No case damage. I'll try to add a picture.

I have decided to use this engine in my 72 bus. I have also decided to install new dual carbs. I have installed a hatch from a late bay in the rear deck to access the engine.

So my question for this post is about the fuel pump. Should I just buy a low PSI electric pump and wire it up? Or should I open up the mechanical port on the case and get the parts needed for the mechanical pump?

Thoughts?
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Wildthings
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PostPosted: Fri Nov 15, 2019 3:27 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

I doubt that you can have it machined for any kind of reasonable cost. It would take a lot to set it up to do the machining.

Electric fuel pumps can work great. I have a low pressure marine Airtex, which is probably 10 years old at this point in time. You can buy special fuel pump relays which will cut the pump off if the engine stalls, so it will not pump fuel in case of a roll over or fire. You can also add a marine anti-siphon valve to the outlet of the tank.
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orangebug60guy
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PostPosted: Fri Nov 15, 2019 3:43 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

I've been running this for years in a split bus with a 34-3 and a bay window dual solex:
https://www.autozone.com/fuel-systems/performance-...lsrc=aw.ds

Image may have been reduced in size. Click image to view fullscreen.
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timvw7476
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PostPosted: Fri Nov 15, 2019 4:39 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

That spun bearing/torn dowel pin is a sign of oil starvation.
As for fuel pump, always go electric, one of the things that make modern
cars modern, as in quick starts, hot or cold, which means short cranking
time. I left mechanical pump behind almost twenty years ago.
The Type IV engine acts like a teenager with a priming fuel pump.
They make vapor lock a thing of the past too.
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CrRusty
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PostPosted: Fri Nov 15, 2019 4:52 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

Ok, It comes back to the gasoline we use today. Ethanol ruins rubber and rubber like parts. OEM parts are not really available. Any flexible rubber part in the fuel system is very short lived, due to ethanol. Being reasonable your best option is a electric universal fuel pump. I concluded a few years ago that Carter fuel pump was the best option. It is widely recommended you also add a fuel pressure regulator. (to some, not always necessary) I found the Holly regulator to have the best reputation.

Replace the fuel lines with new is a must. I'd recommend using Gate barricade fuel lines

Another thought is to use a rubber isolating mount between the fuel pump and vehicle to minimize the pumps motor noise

When you install put in a temporary fuel pressure gauge until you dial in the about 3 pounds of fuel pressure you need. It is Not recommended you keep the gauge on vehicle once it is set up and initially adjusted.

Next step is wiring the fuel pump to power it.
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malcolm2
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PostPosted: Sat Nov 16, 2019 12:08 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

Thanks to all for chiming in.

I have read that a rotary pump is the best option. That is what my 914 has for the FI system.

I will start studying up on the electric pump and plumbing and wiring it properly.

The 914 pump comes on with the key, but after a few seconds, maybe 30, it shuts off if the engine is not running or trying to start. Maybe I can figure out how to wire it up like that. Engine dies and the pump stops, even if the key is on.

Thanks.
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malcolm2
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PostPosted: Sat Nov 16, 2019 12:18 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

THis is the middle bearing cradle. You can see some evidence of "hammering"> I read that this is typical. THe location and the evidence.... which is the bearing stamp being transfered to the engine case. I will need to measure

Image may have been reduced in size. Click image to view fullscreen.


THis is the 3rd bearing. All is well here.

Image may have been reduced in size. Click image to view fullscreen.



THis is the bearing that slightly spun at some point in it's life. Only deformed the bearing 1/4" with the dowel. Might have only slightly reduced the oil coming here.... it is the full circle bearing on the crank, close to the fan.

Image may have been reduced in size. Click image to view fullscreen.

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airschooled
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PostPosted: Sat Nov 16, 2019 12:37 pm    Post subject: Re: Mechanical vs. Electric fuel pump Reply with quote

malcolm2 wrote:
I have read that a rotary pump is the best option. That is what my 914 has for the FI system.

I will start studying up on the electric pump and plumbing and wiring it properly.

The 914 pump comes on with the key, but after a few seconds, maybe 30, it shuts off if the engine is not running or trying to start. Maybe I can figure out how to wire it up like that. Engine dies and the pump stops, even if the key is on.


The 914 uses D-Jet fuel injection, which operates around 28psi. Your carburetors want 2-4psi, depending on make, model, and quality. Rotary pumps are nice, because they're quiet, but you want to make sure that pump pressure matches your carb demands. Even 5psi can flood carbs and cause engine issues sometimes.

D-Jet injection typically runs the pump for a few seconds when you turn the key on to prime the system. The is necessary for FI which requires pressure to run. Since carbs have a bowl of fuel for on-demand use, you'll only need to prime your carbs during setup, and any time you let the car sit so long the fuel evaporates.

Because you don't need the pump when the engine is not running, it is best practice to instal a relay to power the fuel pump. Use a (fused) wire from the starter + terminal to supply power to the relay, and trigger the relay using the alternator blue "idiot light" wire. This does two things:

1) Takes the load off the fuel pump and the ignition switch/wiring.
2) Only runs the pump when the engine is spinning on its own. This will act as a safety measure if you get into an accident and the engine stalls. You don't want the fuel pump to keep pumping in a case like that!

Relay wiring is described here:
https://www.itinerant-air-cooled.com/viewtopic.php?f=50&t=11380

Good luck,
Robbie
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