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Suzuki DF 250 stalling when idling??

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  • Suzuki DF 250 stalling when idling??

    Engine runs fine at all RPM settings, but if I idle it for about 30 minutes it stalls and won't start.
    Pump up soft fuel ball and its game on again only to repeat this scenario if idling for a period of time.
    I replaced the fuel bulb/ball, looked for fuel leaks, seems intermittent.
    Any help out there?

  • #2

    Remove the anti-syphon valve from your fuel tank. They will fail and restrict fuel flow at low engine speeds, and it sounds like yours is on its way out.

    Replace it with a straight thru barb so the issue does not recur. AS valve is not required on outboard powered boats and are just a source of issues.


    • #3
      My fill/vent is integral with the cap. I there a way to fix this or replace the cap?


      • #4
        Not talking about the fill vent.

        Talking about the anti-syphon valve.

        Its the elbow fitting that screws into the top of your boat’s fuel tank, the fuel hose connects to it.

        Most all US built boats have them fitted as standard. There is a valve inside that elbow fitting that is designed to prevent fuel being syphoned out of the tank if a hose accidentally comes off near the engine.

        So the AS valve creates some resistance to fuel moving thru the line from tank to the engine, and if the valve gets sticky, the resistance increases, with the result that its harder for the fuel pump to draw fuel from the tank to the engine. See where this is going??

        In extreme cases, fuel flow can almost be stopped, especially at low engine revs where the demand for fuel from the engine’s fuel pump is low. At higher revs the engines draw more fuel volume which helps keep the AS valve open and allows flow. So problems with an AS valve almost always manifest themselves at idle speeds or very low revs. It can be temporarily overcome by squeezing the primer bulb firmly, but its only a temporary solution.

        Hopefully that explains what the AS valve is and why it can cause problems like you are having.

        To fix it:

        1. Take the fuel line off the tank fitting. Make it safe (Plug it up) so fuel cant run out.
        2.Then you can unscrew the fitting from the tank and either
        (a) replace it with a elbow fitting that does not have the valve components inside (they are just a tiny ball, spring and seat) or
        (b) you can take it off, and punch the fittings out of the inside leaving the elbow fitting empty, and reinstall it.

        A sticky AS valve may not be the problem but theres a decent chance it is. And getting rid of it has no downsides, they are intended for boats with inboard engines where fuel hoses are often connected down low where if they come off they can syphon fuel from the tank into the bilge. Which cant usually happen in outboard powered boats.


        • #5
          I will check to see if I have the AS valve


          • #6
            My tank does not have an Anti-siphon valve. I haven't been able to duplicate the issue on the last trip. It might take a few more hours of idling to resurface.


            • #7
              Check the white wire which runs battery power to the ECU......mine does the same thing and when it happens the trim also does not work so if this is the case this could be your issue. Mine for some reason is a low voltage reading in the wire itself.


              • #8
                I agree , I fixed the white wire earlier. Don't think that this is the problem. I ran it two times since I had the issue and it hasn't resurfaced


                • #9
                  I am having the same problem as straycatboat , shuts down after 1/2 hr idle and will restart after squeezing primer bulb a while. Of course this happens at the worst times, in current near obstacles or other boats.


                  • #10
                    built in fuel tank?
                    check the breather vent.. bugs make nests
                    or if screened could be plugged


                    • #11
                      Yes, 79 gal. Tank. Checked vent, fill cap ok. Replaced fuel pickup on tank no anti syphon ball. New fuel line and water seperator filter, primer bulb. Drained fuel tank. Both low and high pressure fuep pumps come on when ign. Key turned on. 12.7v to white wireECM.
                      the problem is intermittent. I just ran it for 1hr at idle without it shutting down. I hope it is fixed but i have had it reocure before. I run fishing charters and am on the water 3-5 times a week . Much of my time i am in no wake zones with current. It is common for me to idle for over 1/2 hr continuously acouple times each trip. It may run fine a few weeks or days b/4 acting up again. 1550hrs on the suzuki 250.


                      • #12
                        Your fuel bulb is/was going soft/flat like straycatboat? Fuel bulb is sitting vertical not horizontal?


                        • #13
                          When the problem occurs the fuel bulb is soft and when ipump it, it feels like little or no fuel is being pumped. The bulb is located at a 30-45 degtee up. I moved it to 90degree up last night.


                          • #14

                            …..all primer bulbs are not created equal. Suzuki and Yamaha OEM are highly regarded. Many after market ones aren’t

                            ….. air leaks can happen without fuel leaking. Tighten all clamps between tank and engine. Twice.

                            I think these first two are the most likely if you have 200% verified that there is no anti-syphon valve on the tank outlet.

                            ​​​​​​…..have heard of tank pickups being cracked

                            ….. worth having fuel pressure checked.

                            Good luck, these problems can be a PITA.

                            Last edited by Moonlighter; 04-04-2023, 07:02 AM.


                            • #15
                              Would it be feasible to drain the VST once the engine shuts down by itself? It sounds like you MIGHT be having a fuel starvation issue but since it only happens when idling makes me wonder if it really is a fuel starvation issue. One would think if you have a fuel starvation issue wouldn’t the engine shutdown at all revs? The reason I’m asking to drain the VST after it shuts down is the VST should be empty and wound confirm without a doubt a fuel starvation issue. Maybe your low pressure fuel pump is weak and isn’t supplying enough fuel to adequately fill the VST at idle? Checking the fuel pressure as Moonlighter suggested is a cheap easy check. I’m assuming you have traced the entire fuel line looking for abnormalities checking every inch, every clamp. Have you taken apart the rubber grommet where the fuel line and wires enter the engine? Maybe your fuel line is being restricted inside the grommet? I read in a different forum that a guy had a corroded wire inside the grommet that had swelled up and was putting pressure on the fuel line causing a fuel starvation issue. In post #11 you don’t mention changing the inline fuel filter? When it stalls try opening the fuel tank gas cap, if a vacuum has been created you should hear the tank sucking air in and your primer bulb should be sucked flat, not soft but sucked flat. I know you checked the vent, this would be a double check. Have you tried adding a dose of Seafoam or other fuel additive that will emulsify any moisture in your fuel system? It’s cheap and easy to try. In Canada I add Gas Line Antifreeze aka methyl hydrate aka fondue fuel to all my engines in the fall and throughout the winter. The boat gets a dose in the spring as a just in case moisture formed during the winter.