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Eric

From mechanical to electrical fuel pump

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Now that my 620 arrived i have to get it running. Mechanical fuel pump is dead and since there are only a few 4 cilinder L series motors in the country it is not easy to find a replacement. 6 cilinder ones don't seem to fit.

Now i found out the 620's that have AC from factory always use an electrical fuel pump.(at least that is what my service manual says) so thats the way to go i gues. I can find a low pressure electrical fuel pump pretty easy. 

If a 620 has an electrical fuel pump from factory do they have a different fuel tank as wel? And is it as easy as just blocking of the old mechanical fuel pump hole and put the electrical fuel pump in the fuel line between tank and engine and that's it? Or are there any other mechanical modifications necessary?

 

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I dont know about the different tanks... but if the factory electric pump is external then I doubt the tanks are different.

 

Should be a pretty easy swap for you.

 

Remove the mechanical pump and make a block off plate to cover that hole. There are some for sale somewhere for l series engines... but easy enough to make one out of plate or thin bar stock aluminum.

 

Then you just need to install a low pressure fuel pump somewhere in line. 

 

There is likely a soft line connecting the tank to the hard fuel line, that's an easy spot to sneak one in. In my 510 i put the pump in the trunk. On my 620 its mounted to the frame rail.

 

Running carbs it cant hurt to put a regulator in there to, and Webers and mikunis can be pretty picky about fuel pressure.

 

A pretty commonly used low pressure pump is available from Carter, then I think I'm running a Holey regulator to dial it in on my 510 with carbs.

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I think only the '78 or '79 used the electric pump because of the York compressor placement.

 

The Z car mechanical pumps are three bolt mounting.

 

I think a Chevy fuel pump block off plate will fit also.

 

The 720s used electric pumps at about 3 PSI... except the Z24i with EFI. Those were high pressure.

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Maybe the fuel tank is different because of a fuel return line? 

I can make a block off plate, this easy. Pump can be somwhere under the cab. Maybe a return line? There is a Weber carb. on my engine now

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Fuel return lines were used on the L20B or from '75 and on. Strictly speaking you don't need one for either pump... it has no effect on pump pressures. It was used to simply circulate cool fuel past the carburetor to prevent vapor lock and hard re-starts when hot out. There is a plug in the return with a small pinprick hole so there is resistance and the pump can build up some pressure, else the fuel would ignore the carb and simply go down the open return line to the tank. Another advantage of the return line is that slowly all the fuel in the tank is circulated through the fuel filter and cleaned over and over preventing an accumulation of debris in the tank bottom.

 

11aMYIJ.jpg

 

The bottom rubber hose would be from the mechanical pump. The top one goes back to the tank. You can see how tiny the hole is.

 

 

All liquid pumps suffer from the same thing, they can produce thousands of pounds pressure but they suck at sucking. No pump made will draw water vertically more than about 30 feet. This is limited by atmospheric air pressure, so mount your pump as low and close to the tank as possible. If you can.

 

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Hm, my '73 620 has a return line.

 

Oh, and Holley pumps suck the most (figuratively).

Newer Carter pumps (now made in china) suck almost as bad......
The Z-car FI pump doesn't suck, it just puts out way too much pressure for a carburetor, unless you replace the relieve valve spring with something much lighter.

Older Carter performance pumps don't suck, if you can find old stock, but must be run with a low pressure bypass regulator.

 

I miss the simplicity of gravity feed, like my race bikes had, no frigging pump needed......

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well i live in the netherlands and holley and carter are no brands widely available here so i have to find something else that works. if there is a return line the carb can't get to much gas right? any exces fuel will get in the return line?

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8 hours ago, Eric said:

well i live in the netherlands and holley and carter are no brands widely available here so i have to find something else that works.

 

Your like eight hours from England! There are a plethora of racing equipment shops at your disposal. Find a low pressure Facet pump.

 

https://www.merlinmotorsport.co.uk/knowledge_base_articles/view/facet-fuel-pumps-for-vehicles-running-carburettors-282

 

https://www.fuelpumpsonline.co.uk/

 

https://www.burtonpower.com/parts-by-category/fuel-system/fuel-pumps-carburettor.html

 

 

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2 hours ago, datzenmike said:

https://www.burtonpower.com/facet-electric-fuel-pump-kit-silver-top-4-4-5psi-fac476087k.html

 

FAC476087K_Pump_Kit.jpg

 

This physically, looks identical to the 720 electric pumps. PSI is the lowest and closest to stock.

It also looks just like the Bendex pumps found in older small aircraft and small British tanks, the ones I own work well and are nicely cleanable.

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14 hours ago, Eric said:

if there is a return line the carb can't get to much gas right? any exces fuel will get in the return line?

 

Well, not quite.

The bleed hole in the return line won't pass a whole lot of flow, so be careful.

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