won't run and occasional backfire

[Lumps]

Hi All,

I have a 2000 seadoo challenger 2000 with the mercury 240 EFI engine.

It was running last year but would not start this year. the fuel was very old (quite brown) I replaced the fuel and now it will start for a second before stalling. repeated attempts cause a backfire. Old fuel has has been replaced with new fuel and i drained as much out of the vapour separator and water filter. fuel looks clean and no water. port side temp sensor was replaced. and I cleaned out the fuel filter. still not running more then a second then stalling (in trailer). but a after repeated attempts to start it, it will let out a massive backfire.

I thought there was just still old fuel and that it was just a matter of time before the clean fuel made it in. but with the back firing im worried that im causing damage.

Anyone have ideas what I should look at?

 

[ripcuda]

I would pull the spark plugs, inspect... then do a compression test on the cylinders. Good place to start. I would also with the plugs out... stick a spark plug in #1 coil plug wire, ground the plug and put a timing light on that coil wire. Now crank the engine over and verify proper timing of the engine. Additionally, I would pull the ECU and intake off front of the engine to get to the fuel injectors. Sounds like possible leaking injector... leaking fuel in to the intake which eventually causes a backfire. Test high pressure fuel pressure also. Could have an issue with the HP fuel pump (in the VST) too. GL.

 

[Tim75]

I would pull the spark plugs, inspect... then do a compression test on the cylinders. Good place to start. I would also with the plugs out... stick a spark plug in #1 coil plug wire, ground the plug and put a timing light on that coil wire. Now crank the engine over and verify proper timing of the engine. Additionally, I would pull the ECU and intake off front of the engine to get to the fuel injectors. Sounds like possible leaking injector... leaking fuel in to the intake which eventually causes a backfire. Test high pressure fuel pressure also. Could have an issue with the HP fuel pump (in the VST) too. GL.

Backfiring on a 2 stroke?
Maybe slip a camera through the throttle plates and look for damaged reeds?
Or maybe the timing is way off.