forum Forums Technical Engine won't keep running

This topic contains 7 replies, has 5 voices, and was last updated by  jtdesign 4 months ago.

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  • #11653


      I’ve started the engine (1999 Bassa, EFI), a few times now, and typically what happens is it will run quite smoothly for 20 seconds or so, and then starts backfiring, and then dies. Fuel pump problem ? The fuel pump seems quite loud when I turn on the ignition.

    • #11654

        A loud fuel pump usually means its starved of fuel. Is your tank vented ? Try it with cap off.

      • #11655


          The pump IS below the fuel level? They are gravity supplied and will not lift (“suck”)

        • #11656


            Well, I tried it with the cap off – no difference. The fuel pump is in the “normal” place – on the two rear cross members in the transmission tunnel, which actually puts it at about the same height as the bottom of the fuel tank, and based on Ian’s (?) suggestion, I realized that I had only put a few inches of petrol in the tank, so not much head, so I put more petrol in (at least half full now), still to no avail – same problem. Seems to definitely be a fuel starvation problem, because it won’t fire if I try to start it immediately after it shuts down, but after 5 minutes it starts right up again.
            I washed the tank out quite thoroughly before I installed it, but I’m wondering if some sort of debris is blocking the filter I installed ahead of the fuel pump.
            I’m hoping I can put a clamp on the tubing between the tank and the pre-filter so that I can stop the flow, in order to take out the filter and check it, but “unfortunately” I used metal braided tubing to go from the tank to the pre-filter because that was the only way I could make the 180 deg. bend without kinking, which may be difficult to clamp sufficiently tight to stop the flow – we’ll see.

            Thank you for your suggestions


          • #11658


              If you’re running an EFI system then as you’ve said, when you first turn on the ignition the pump runs for about 20 seconds and then stops, this is normal behaviour. Once the engine is started the pump runs continually with excess fuel being returned to the tank via the return hose which I assume you have. If so, you could check that fuel is getting back to the tank when the engine is running.

              The fuel injection system is setup for the bike air filter so if you’ve changed to K & N filters or even have no filters it might be contributing to the problem in that the mixture is weakened and unless you have a Lambda sensor installed the ECU won’t automatically compensate for that change. Having said that I’m running K & N filters on my Californian EFI engined Trikingand didn’t change any of the ECU setup and it runs well.


            • #11659


                Not sure which ECU you will have on his engine but guess it might be an IAW15M. It sounds like the engine is running very lean and will only operate whilst the warm-up enrichment is active in the ECU. As soon as the time/revs enrichment runs out it stops.
                I would check the throttle position sensor output. If it’s a 15M ECU then you should be able to measure about 0.5V on the throttle potentiometer at its idle position. This is, I believe, across the two outer terminals of the three. If you have a different type of ECU then please ignore the above.
                If the voltage differs significantly from the 0.5V then that may well explain why the engine will not run – you will need to re-align the sensor (instructions on the web) and re-set and balance the throttle bodies.
                Sorry for the guesses in the reply but I don’t have much hands-on experience with this particular EFI system.

                Good luck, John

              • #11665


                  Strange – I took out the pre-filter which I’d installed between the petrol tank and the fuel pump, and which seemed perfectly clear, and now the engine seems to run fine. The filter I was using was just a cheap generic fuel filter, (see photo) and I’ve noticed in photos of other people’s set up’s they’ve used somewhat more exotic filters – could this have something to do with it , and is there a recommended type of filter for this location ?

                  As an aside, I looked into the possibility of measuring the throttle position sensor voltage, and that looked quite difficult, since it’s buried under the throttle mechanism and intake manifold – I have a hard time plugging and unplugging it, let alone reading any voltage

                  Thank you for your suggestions, Dave, John, etc.


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                • #11667


                    Great that you’ve got the problem fixed – well done. The pumps are designeed to run with a small positive pressure at the inlet so evidently the filter was too restrictive and resulted in low fuel pressure. Dave’s suggestion to check for fuel return from the pressure regulator is great to make sure the pump and filters are working properly.


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