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How much pressure does a stock mechanical fuel pump have?

Discussion in 'The Hokey Ass Message Board' started by Rpmrex, Apr 4, 2012.

  1. Rpmrex
    Joined: Nov 19, 2007
    Posts: 660

    from Indiana

    I have a 350 with a stock fuel pump and just bought 2 rodchester carbs set on a vintage speed 4 to 2 adapter. Will I need a regulator or does the stock chevy fuel pump not pump enough to wory about it?

    How much does a stock pump, pump?

    Whats the best pressure for the rodchester 2G's?

  2. Stroker McGurk
    Joined: Feb 17, 2012
    Posts: 293

    Stroker McGurk
    from Canada

    Stock pump is usually under 6 lbs, which should be fine for those carbs
  3. Mat Thrasher
    Joined: Nov 5, 2007
    Posts: 1,062

    Mat Thrasher

    I don't know about the pressure of a mechanical pump. But I run my 2GC's at 3 PSI. It seems to work good on my set-up.
  4. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,481

    from Oregon

    I'd put a pressure gauge inline after the pump. I've seen stock SBC mechanical pumps put out as high as 9 lbs., and when they do they always cause carb problems. Been there, done that.
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  5. XXL__
    Joined: Dec 28, 2009
    Posts: 839


    3-4# is good for those carbs. Mechanical pumps are all over the place, depending on manufacturer, model, batch, condition, etc. Stick a gauge on it, at least... so you know what's going on, and possibly a regulator so you don't feed the carbs too much.

    Edit: What the post before me said.
  6. n847
    Joined: Apr 22, 2010
    Posts: 2,695


    I would expect 3-5 lbs if its a bone stocker but we put one on a stroker motor that ran 7-9 and it "looked" like a bone stocker!
  7. My stock pump runs about 5-6 lbs. I also run about 3 lbs on my 2gs. You will probably need a regulator but you could try it without first and see how it goes.
  8. Just a thought,,,,,

    Every pump is going to be a little different, so far on this thread we've heard from 3 to 9 psi.
    It's imperative that you know the pressure going into the carb in order to properly tune, diagnose, and troubleshoot any fuel delivery problem.

    ,,,,, after you get it mounted put a gauge on it. Make your call on a regulator then.

    record the pressure someplace as " fuel pressure new psi X " that way in a few months when you want to post a " car acting funny, why ?" Thread, you'll be able to tell what was and is the fuel pressure. That will save you so much tail chasing.
  9. putz
    Joined: Jan 22, 2007
    Posts: 470

    from wisc.

    3 pounds...............
  10. carbking
    Joined: Dec 20, 2008
    Posts: 2,055


    How much does a stock pump pump? Depends on the design and quality control of the pump. Even some name brand pumps produced today (made in a different country) have been measured above 15 psi!!! A fuel pressure gauge is going to be your only definative answer.

    What is the best pressure for the Rochester 2G? Depends on fuel valve orifice, float height, and the bouyancy of the float used (several different were used in various 2G series carbs). With a STOCK tripower on a 1964 GTO I ran 5 1/2 to 6 psi with zero issues. Carbs were originals, with original floats, and the correct fuel orifices.

    Edit - the phone hasn't started yet, so checked two common 2G fuel valves used by Chevrolet: one was a 0.082 orifice, the other 0.120. I suspect if one checked some other brands (maybe the 2G used on the Pontiac 455 and the 2G used on the Mercury marine small six) the range would be even greater. Now which valve is in that universal kit you buy at the FLAPS that services 792 different carburetors?

    Last edited: Apr 5, 2012
  11. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,807


    Got a large base brass float 2G being fed with an electric pump at 5 psi.No flooding or rich idle problems even after a hot restart.
  12. tommy
    Joined: Mar 3, 2001
    Posts: 14,763

    Member Emeritus

    I've never had a problem with the Rochester carbs. I ran a Rochester on my old Chevy with an electric pump and no regulator. The Rochester carbs came stock from the factory on Chevys on a stock mechanical pump and no regulator. It's the 97s and 94s that seem to be more pressure sensitive.

    That being said I have 2 97s running on my stock Studebaker mechanical pump with no regulator at all. I bought it that way and the need never came up. I bought a kit and rebuilt the stock pump. I don't look for problems so I just go with the flow if it wants to flood then by all means add a regulator but I don't assume that there will be a problem before it occurs.
    Electric pumps with 97s are different animals of course. IMHO.
  13. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,846


    GMC Bubba has a great tech on testing fuel pressure W/O a guage

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