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What would cause a fuel line to not allow fuel to flow from the fuel pump.

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  • What would cause a fuel line to not allow fuel to flow from the fuel pump.

    Hello- I have a Tohatsu M70A2 late 80's motor. It runs good but I have a problem with a fuel line.

    Took the boat out and ran out of fuel in the first tank. We''s call this tank A. I switched to the second tank (we'll call this tank B), pumped the bulb until hard. Started the motor and it would stop after the fuel in the carb bowls depleted. I went through this cycle a few times. Eventually I poured the gas from tank B into tank A and solved the problem. The fuel pumped from the tank to the carbs without a problem.

    I figured the tank was the problem, so I bought a new tank. I took the fuel line from tank B and put it on this new tank. Today, after I ran out of fuel in tank A, I hooked up the new tank, and had the same problem. Once the fuel in the carb bowls had depleted it would cut off unless I pumped more fuel using the bulb.

    What would cause this phenomenon? Has anyone else experienced this?

  • #2
    My understanding is you have 2 tanks and 2 fuel lines. The tank didn't fix the issue and there is still no issue running frm tank A or the A fuel line. I would guess there is a fuel line B problem
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
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    • #3
      Your correct on your summary of my problem. I've never heard of a fuel line problem. I mean by process of elimination it must be the fuel line, but what in a fuel line would stop a fuel pump from pulling fuel through? It boggles my mind.

      Thanks for the response.

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      • #4
        The ethanol proof liner degrades and blocks free flow of the fuel. In my opinion, the hoses are fine if E-10 doesn't sit in the hose. It's all the non-use most of our boats see and hoses aren't drained.
        BOAT SPECS | FORUM HELP | STARCRAFT FORUM | SHOP iBoats
        Please, no PM's (Private Messages) regarding boat/engine problems.
        That is what the forums are for.
        Only forum/moderator issues will be answered in PM's.

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        • #5
          Also, a leaky o-ring at the tank end can cause air to enter instead of fuel.
          Paul
          Certified Tohatsu TLDI Technician
          Buffalo NY USA

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          • #6
            I like the sucking air theory, but it could be that the hose is collapsing internally when fuel is being sucked through it, but fine under pressure from the primer bulb too.

            Noteworthy maybe, I've heard of a couple instances of this, as well as rubber particles breaking loose and plugging filters on the newest EPA compliant hoses. FWIW, -Al

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            • #7
              Or you might have a sticking ball in the one way valves of the ball pump, but this is minimized by you ability to pump. y guess you have an air leak in the Tank B line assembly. Eliminate each component, 1) tank connector; 2) tank line to bulb; 3) bulb; 4) tank line from bulb to engine; 5) engine connector. If you have a switch between the two tanks then eliminate that.

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              • #8
                Easy enough to check if it's the hose - Switch Hose A to Tank B and vice versa.
                BOAT SPECS | FORUM HELP | STARCRAFT FORUM | SHOP iBoats
                Please, no PM's (Private Messages) regarding boat/engine problems.
                That is what the forums are for.
                Only forum/moderator issues will be answered in PM's.

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                • #9
                  Outwards appearance of fuel line looking prefect doesn't mean inside issues are not the problem. Looks can be misleading... Now where did I hear that one before?
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                  • #10
                    Thanks everyone. I ordered a new hose and engine connection.

                    Comment


                    • #11
                      OEM Tohatsu fuel lines don't have any internal sleeve found in other fuel line brands which deteriorate and break in tiny pieces specially with E fuels use that will clog them very easily when this issue happens. The quality is so darn good that will keep sending fuel through them no matter being excessively hardened by the sun..

                      Happy Boating


                      Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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                      • #12
                        I received a new fuel line today. I hooked it up to the same motor connector, and the same issue persisted. I find it strange that the fuel filter has fuel in it when the carburetors run out of fuel. I get a new fuel line to motor connector tomorrow. I will post back. And thanks for all your help.

                        Pete
                        Last edited by Petedacook; September 15th, 2020, 07:45 PM.

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                        • #13
                          Originally posted by Petedacook View Post
                          I received a new fuel line today. I hooked it up to the same motor connector, and the same issue persisted. I find it strange that the fuel filter has fuel in it when the carburetors run out of fuel. I get a new fuel line to motor connector tomorrow. I will post back. And thanks for all your help.

                          Pete
                          When you say you "hooked it up to the same motor connector", does that mean you connected a rubber hose to the same connector you were using before when you were having the problem? If so, did you check that connector to see if the O-ring was intact inside?? That was what Paul was alluding to in his earlier reply. An air leak there would cause your symptoms.

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                          • #14
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                            Some issues :

                            (1) Both the motor male connector as well as the tank's male connector must be smooth when finger rubbed for the small o'rings inside the female connector ends to connect/hook well, if with visible scratches will let air in and motor miss specially at higher rpm range. If with tiny scratches can micro polish them with toothpaste, carburundum (used to polish valve seats) or any other thin particle polisher.

                            (2) One cheap way to determine is having air leaks in any side of the hose connector is to wrap some 360 rounds of any electrical or duct tape in the whole extension of the male/female connector as to rule out having already any air leak. Connector must be perfect clean for the tape to adhere and seal properly.

                            (3) It's normal for the fuel filter to remain with a lot of fuel when carb, carbs have been run dried. If wanting to disappear the most filter content, keep pressed the motor male connector pin down or hook a spare female connector and throttle back and forth for fuel located inside the filter to pass to carb and be burned.

                            Would recommend to lube both o'rings located at both female ends with olive or cooking oil applied with a Q-Tip as not to rub the o'rings dry when connecting onto the male connector, will last near forever specially if the hose is connected/disconnected frequently.

                            Happy Boating


                            Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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