Cannondaleriders

So i changed the crank and installed a 450cc kit, I tried to start the engine and no luck I pull started and it runs but I give some throttle and will die.. It wont start by the switch only push started.

I have spark
fuel into the tank
new fuel pump
checked reg

I also have a new etc but it has stamped with marker atk atv mx, I dont know if this ecu will work for me, since I try to connect and Im getting the error 125...

What else I should check?

Reversed fuel regulator lines/loose ground on frame at the regulator? I had similar symptoms once and turned out to be both those things after a rebuild. Impossible to start by starter but when pushed it would run for a short bit. Dead upon throttle.

If good then from what it sounds, you haven't tuned it. Going to a 450 from 432 will require a throttle recal, remap, etc. That would definitely be a big possibility as well. Before you keep trying to start it, get the ecu setup for what you have, throttle recall, etc.

Hopefully you are not using the stock air box because the next thing that I would check would be to make sure both injectors are working by looking down at them while cranking. I have had one stick after a rebuild and give the same symptoms... Did you do the throttle cal and sure that you got that right?