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What do fuel pumps do without DC? 200 '82

posted by  someone claiming to be Evan R on  Mon Dec 11 07:52 CST 2000 [RELATED]

Hey all. I'm getting all the parts together for my B21K mod.

B21FT downdraft manifold mounting a used Weber DGV. Neat, eh?

I plan on using an aftermarket fuel pump at 5 GPH. Here's what I need to know...

a]will the stock prepump allow fuel to be sucked through it if no DC is supplied? I'd just as soon leave it alone if I can.

b]can I just use plain ol' fuel line from the top of the tank to the inline filter?

TIA,

Evan







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    Re: What do fuel pumps do without DC? 200 '82

    posted by  someone claiming to be Gene Stevens on  Wed Dec 13 02:03 CST 2000 [RELATED]

    The in-tank pump is a small centrifugal pump, much like the water pump or a "squirrel cage", and it will have no problem passing liquid directly through it without power.

    Here's a suggestion; use the original pump to feed the carbs directly. It should have both the pressure and more than enough volume for your needs. If you're not comfortable with that, install a "tee" on the suction side of the mechanical pump and a small restrictor leading back to the return line. The mechanial pump won't have to work as hard by delivering fuel right to its inlet.







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    Re: What do fuel pumps do without DC? 200 '82

    posted by  someone claiming to be Don Foster on  Mon Dec 11 13:04 CST 2000 [RELATED]

    "..will the stock prepump allow fuel to be sucked through it if no DC is supplied?"

    Why don't you pull the fuse, depowering the tank pump, and see how well the main pump sucks fuel?



    Don Foster (near Cape Cod, MA)







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      Re: What do fuel pumps do without DC? 200 '82

      posted by  someone claiming to be Evan R on  Mon Dec 11 19:30 CST 2000 [RELATED]

      From what I know, pretty decently until the tank gets low, Don. But the Bosch main pump is trying to do A LOT of work pressurizing the fuel.

      I guess I don't understand the physics involved. It doesn't seem like it would take a whole lot of suction to create the flow rates and pressures necessary for a carb'd engine.

      What's in the tank of a B21A car? Just a sock and a sender?







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        Re: What do fuel pumps do without DC? 200 '82

        posted by  someone claiming to be Don Foster on  Mon Dec 11 22:26 CST 2000 [RELATED]

        Evan --

        That's not really a fair test. You must open the main pump outlet and allow it to discharge to atmosphere—it's the "delta-P", or pressure difference that the the main pump responds to. When it's still connected to the FI system, it sees a significant head pressure (as if it were blocked). This is why it strains and whines.

        The other issue is knowing the internal design of the tank pump (and I don't know it). If it's a "constant pressure" type, then it's a vane or blade pump (somewhat like a fan). You can easily pull liquid past this pump.

        But if it's a "constant discplacment" pump (like an oil pump or the main fuel pump) then you cannot pull fluid past it.

        "What's in the tank of a B21A car? Just a sock and a sender?"

        Don't know.



        Don Foster (near Cape Cod, MA)







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    Re: What do fuel pumps do without DC? 200 '82

    posted by  someone claiming to be Les Lyne on  Mon Dec 11 09:07 CST 2000 [RELATED]

    This isn't answering your question, I realize, but isn't a DGV a carb meant for a VW? That in and of itself isn't bad, of course, but does it have the flow rate that you want?

    Another carb that you might want to consider is a Weber DFEV. This is a 32/36mm progressive, with mechanical link for the secondary. Fiat 2.0 guys use these carbs with good results (and a Fiat 2.0 is good for 7500rpm with good valve springs).

    Or even better would be a pair of 40 DCOEs! But I realize you probably already have the DGV so forget the DCOEs . . .

    BTW, does the float in the DGV line up in the proper direction when installed on a Volvo engine?







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      Re: What do fuel pumps do without DC? 200 '82

      posted by  someone claiming to be Evan R on  Mon Dec 11 12:06 CST 2000 [RELATED]

      Well, I got the DGV off a conversion kit I found in the boneyard on a 2.3 liter Mercedes. That motor is a heck of a lot like a B21F, so I figure it'll be fine.

      > BTW, does the float in the DGV line up in the proper direction when

      > installed on a Volvo engine?

      Dunno. What's the proper direction? I've never carb'd an inline 4 before. The adapter plate I'm designing is set up so that I can use the accelerator cable as is from the K-Jet. If that's not right, I can always get a different cable.







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        Re: What do fuel pumps do without DC? 200 '82

        posted by  someone claiming to be Les Lyne on  Tue Dec 12 16:07 CST 2000 [RELATED]

        If you've pulled the carb off a Mercedes, it will be oriented properly. You'll be ok.







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        Re: What do fuel pumps do without DC? 200 '82

        posted by  someone claiming to be Evan R on  Mon Dec 11 12:13 CST 2000 [RELATED]

        My bad - I just double-checked. The DGV and DGEV are the same carb, except for the "E". That stands for "E"lectric choke.

        I'll need to get a choke cable setup from a B21A.






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