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?