SeaDoo 787 RFI new engine won’t run

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I have a 2000 GTX with a new SBT reman engine and it just will not run. I checked the timing 3 times and the rotary valve is exactly right. It will start running then backfire and stop. What else can I check?
What happened to the old engine.

Fuel injection timing and leaking injectors can also cause backfires.
They guy that had it before me purchased the SBT motor with the 2 year warranty and put it in himself but had a local shop inspect it but the new motor seized up after running a few minutes. I purchased the ski. Since under warranty I sent the motor back in and got a replacement. I found the issue when removing the motor, the plastic coupler that goes from the crank to the oil pump had all its teeth ripped off, I think he reinstalled it on the new engine and seized it right away from lack of oil. Tell me more about the timing for injectors and how to set it. Also maybe the rotary valve cover is out of spec? I thought I checked that but it has been a year since I worked on the ski. I do have another identical running ski I can swap out parts to test.
Did you test your fuel pressure? Are the injectors firing? How is the spark? Make sure you have the electical plugs where they belong as some can be confused. Do you have new spark plugs installed? That's just for starters. Download the manual, get out the ohm meter and starting checking the readings.
I will check those out. It did start and run but it ran rough like it was not timed right. It had to be fuel, spark, or air. I did compare to the other ski so I do know I have the wires right.
The plug for throttle position sensor and Air Pressure Sensor can be swapped. There is a plug near the fuel injectors that can be mistakenly swapped as well. Those are just quick things to check. Then, as I mentioned, I'd pull the #4 terminal on the computer and check all of the components, such has TPS, Air Pressure Sensor, Fuel injectors, Crankshaft sensor, Air Temperature Sensor. Make sure you're rave valve system is connected properly and the check valve is checking. :)

Not sure if you swapped the Rectifier. That and charging the battery fully are the first things I would do. Good Luck !!
Thanks so much for the advice. I’ve had the thing 2 years now and it hasn’t run yet. I’m looking forward to trying out your suggestions. I do have the manual. I will let you know how it goes.
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