Hi!
I have XTX, but my wife is riding Aprilia Pegaso with the same engine. I've decided to ask this forum, cause Aprilia forum looks not good enough in tech questions.

Summary:
I can start engine at the morning without any issues. It is running just fine. It is revving fine as well. Nothing special, normal engine work. But when I'm trying to take a ride - it is working fine only till I give it a full gas (trying to accelerate) on 2nd or 3rd gear (i.e. while moving). At this same moment - engine just stops. And it won't start again no matter what you do. It's just turning and "catching", but not starting.
2 days - same situation. I gave it 15 minutes to work on idle -- no problems! But is stalls on full gas while riding and won't start till next morning.

What I've checked so far:
1. Spark plug - nice spark each time starter rotates engine. Changed spark plug -- no difference. Checked the plug right after engine stops this morning - dry and clean.
2. Fuel pump - I've disconnected the pipe from the tank, closed the hole with my finger, and turned the key on - the pump started working and I can feel the pressure, but I can hold the finger so no fuel leaks. Is it ok, or is it low pressure?
3. Injector -- cleaned with special equipment. I took injector out of throttle body and tried to start the engine. I got nice clean cloud of fuel out of it. It is comparable to a pint glass by a volume. Looks OK to me, but I have no experience to compare.
4. Fuses - changed. Were OK and are OK.
5. Battery - new. Charged.

????? What can be a reason for engine to stop on full gas while moving, and then not start no matter you do? But start again next morning just to repeat everything again?

Standard exhaust. O2 sensor is there. The weird thing here is that it was working well on idle for about 10 to 15 minutes, I was able to stop the engine and start it again. No problems. And then I gave it a short ride, but when I gave it a full gas - it died at the same moment and won't start again. But it will start again next morning...

Blocked/dirty air filter? Collapsing catalyst/partially blocked exhaust? Dodgy TPS maybe?

__________________

hi this is for the Yamaha electical system but should be almost the same.

The self diagnosis have multiple fault singnals that can stop the engine for failsafe.

1. crankshaft posision sensor.
2. broken or disconected Blue/black lead of the ECU.
3. lean angle cut-off switch (mc has turned over)
4. faulty ignition (ignition coil)
5. lean angle cut-off switch (short or open circut)
6. start unable warning (relay)
7 ECU (signal/contact(short/open circut.)

__________________

XTX 2011. Yamaha Hand Guards, Akrapovic slipon mufflers, Snorkel removed, Airbox drilled, AIS Blocked, PCV, Dynojet Autotune, Kev O2 Controller, Dna Stage 2, KN air filter, mini indicators, steel sprocket cover, cnc levers, cnc mirrors.

What is the round thing at the end of injector rail> Can it be dirty and can it be cleaned?

Fixed! Changed fuel pump and filter. I've tested it in hard mode with the gas fully opened, and it is working just fine.
I think the pump was half-dead. It was able to pump the fuel while cold, but when it gets overheated - just stops giving full pressure.

Thanks for all of your advices.

I've put different fuel pump inside. It is a Bosch pump (15$) that is used in lots of cars, and looks like same pump is sold as spare part for XT660. I had to remove fuel level sensor(useless) for now, to fit the new pump.