RB Fire 11, 7 port engine problems!

[HyperLiam]

Just bought a RB Fire 11, 7 port engine and having problems. To start with the flywheel seems incredibly stiff to the point it just locks up even with plug out. when it does eventually start it sounds rough as hell runs for 20secs max even with tickover up slightly then suddenly stops with a crack. Is this a problem or just a persevering running in issue? Any help would be great, cheers.