after 49k the aerox has died but how?

veyr proud of my aerox never let me down until sunday night. i dropped the weights of my rollers slightly after changing to a weaker torque spring. it seemed fairly revvy but i had my earphones in so couldnt tell how bad.

i was going along a straight and a ifelt the bike stutter and then completely die out. i know its not out of fuel.
it seems IMPOSSIBLE to kick it over. you have to literally kick t really hard it feels like it has all the compression in the world. but its not going anywhere.
it is a standard crank on 70cc i might add. anyone know what it might sound like. all i know is that it kind of studdered and then cut out. and when you push it along you can hear like a knocking sound. it is relcutant to kick over allmost like the crank is locked up or something

 

siezure? whip barrel off and have a lewk