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OT Small motor carbs, gravity feed vs pump?

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  • OT Small motor carbs, gravity feed vs pump?

    I am fixing up an old briggs 16hp single banger. I've already went threw the carb and now I am onto the lines and pump but a question arose. The fuel tank is a foot+ above the carb, the motor has a fuel pump on it originally but the motor is in a different chassis than original. Does the carb need the fuel to be pumped or would a gravity feed be ok? I see talk about different carbs for gravity feed but then I see some guys say most carbs can be gravity fed.
    Andy

  • #2
    Most can be gravity fed, but some pumped carbs will have a higher pop-off pressure on the float valve. Why not just leave the fuel pump in the fuel circuit?

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    • #3
      Originally posted by vpt View Post
      I am fixing up an old briggs 16hp single banger. I've already went threw the carb and now I am onto the lines and pump but a question arose. The fuel tank is a foot+ above the carb, the motor has a fuel pump on it originally but the motor is in a different chassis than original. Does the carb need the fuel to be pumped or would a gravity feed be ok? I see talk about different carbs for gravity feed but then I see some guys say most carbs can be gravity fed.
      I don't know of any Briggs and Stratton carbs that can't be gravity fed, unless they don't have a float bowl. I do know that there are two types of fuel filters though, one for Briggs engines with fuel pumps and one for engines without. I noticed this at the local NAPA last time I replaced the filter on my 11HP horizontal shaft Briggs. I suspect the ones for engines with fuel pumps won't work well with gravity feed. At 1 foot above the carb you should have around .4 PSI (four tenths) approximately due to gravity maybe a tenth or so less.

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      • #4
        Originally posted by lakeside53 View Post
        Most can be gravity fed, but some pumped carbs will have a higher pop-off pressure on the float valve. Why not just leave the fuel pump in the fuel circuit?
        I haven't opened it up yet but I am suspecting being dry for 20 years may have ruined it. Not that I am cheap and don't want to buy one, the simpler the better to prevent breakdowns is more on my mind.



        Originally posted by firbikrhd1 View Post
        I don't know of any Briggs and Stratton carbs that can't be gravity fed, unless they don't have a float bowl. I do know that there are two types of fuel filters though, one for Briggs engines with fuel pumps and one for engines without. I noticed this at the local NAPA last time I replaced the filter on my 11HP horizontal shaft Briggs. I suspect the ones for engines with fuel pumps won't work well with gravity feed. At 1 foot above the carb you should have around .4 PSI (four tenths) approximately due to gravity maybe a tenth or so less.


        Thanks much! I'll check for a filter tomorrow and set it up. I have to go pick up the hose a starter solenoid, and stuff anyhow.
        Andy

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        • #5
          At 16 Hp and a single cyl. engine i,m guessing this is an older Briggs that came with the "Flow-Jet" carb.

          Didn't know they came with a fuel pump.

          The first two didgits of the model number are the cubic inches , check with a briggs dealer preferably an older one to get a positive I.D. on this engine.

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          • #6
            With out the fuel pump you may need a shut off?

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            • #7
              A bit off topic but: My 79 buick V6 in my model A is gravity fed. My .02, Wayne.

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              • #8
                Originally posted by sasquatch View Post
                At 16 Hp and a single cyl. engine i,m guessing this is an older Briggs that came with the "Flow-Jet" carb.

                Didn't know they came with a fuel pump.

                The first two didgits of the model number are the cubic inches , check with a briggs dealer preferably an older one to get a positive I.D. on this engine.
                I found two stickers on the engine. One says 16hp briggs, and the other says synchro balanced. lol Its is old

                Originally posted by flylo View Post
                With out the fuel pump you may need a shut off?

                The carb does have a bowl with needle. The needle should stop and hold the fuel I would think. Even with the pump, the fuel tank above carb and fuel pump would be the same deal wouldn't it? From what I remember the fuel pump on these small motors can "flow threw" without the motor running.
                Andy

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                • #9
                  Originally posted by vpt View Post
                  The carb does have a bowl with needle. The needle should stop and hold the fuel I would think. Even with the pump, the fuel tank above carb and fuel pump would be the same deal wouldn't it? From what I remember the fuel pump on these small motors can "flow threw" without the motor running.
                  Correct and correct. I wouldnt worry about the fuel pump unless youre running a filter. My old Cub Cadet has a Kohler, didnt come with a filter, Ive never added one, and its run fine for 40+ years. OTOH, Ive eliminated the fuel pump on several motorcycles (when they puked) and gone with a simply gravity feed system through a filter without issue.
                  "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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                  • #10
                    The model, type and serial number should be stamped in the fan shroud.

                    Sometimes it is small letters and hard to see, especially if it's been painted over a few times.

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                    • #11
                      If that needle is on the bottom of the carburetor it is more likely the high speed jet adjustment.

                      The engine will run without the pump and I would install a shut off valve somewhere between the tank and carburetor. You can find small inline fuel filters at any lawnmower shop.
                      Gene

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                      • #12
                        Originally posted by topct View Post
                        If that needle is on the bottom of the carburetor it is more likely the high speed jet adjustment.

                        The engine will run without the pump and I would install a shut off valve somewhere between the tank and carburetor. You can find small inline fuel filters at any lawnmower shop.
                        It may have the high speed needle on the bottom, but he already stated he had been through the carb, and it has a float bowl and the needle should shut off the fuel flow.
                        James

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                        • #13
                          Originally posted by J. Randall View Post
                          It may have the high speed needle on the bottom, but he already stated he had been through the carb, and it has a float bowl and the needle should shut off the fuel flow.
                          James
                          It will shut off the high speed circuit. Fuel can still flow into the carb past the float needle. I think its best to be able to shut off the supply of fuel to the carb when the engine isn't in use. Should the float needle fail to shut, the fuel will overflow and those carbs do not have an overflow vent.
                          Gene

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                          • #14
                            I have to agree with topct as well about a fuel shutoff valve on any gravity fed fuel system.
                            Yes 99.9% of the time the needle and seat from the float system will shut off the fuel. But in the event that needle and seat fail to close fully you will end up with an engine full of fuel.
                            When an engine is stationary for long periods of time a very small piece of debris on the needle and seat will allow fuel into the float bowl and eventually into the engine.

                            The fuel shutoff valve for gravity fed systems is universal, just look at any non-fuel injected MC with an above engine fuel tank.
                            It's not if it's going to happen but when.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

                            Location: British Columbia

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                            • #15
                              I agree with the idea of installing a shutoff valve between the gas tank and the carburetor. Parts for a lot of my older equipment are now only available as Chinese replacements. Fuel system parts are pathetically poor, and many of the Chinese needles and seats I've bought have leaked right out of the box, and never do seal well. I never had that problem with US made parts.
                              Last edited by Bill736; 10-09-2012, 05:02 PM.

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