engine locking up???

i have been thru 2 engines, and they both have locked up on me, im not doing anything wrong. it just shuts off and the pull sharter gets locked up, the bike moves back n forth. i took apart the first engine, fixed it, put it back on, and it still locked up after 3 pulls. please help, thanks!

You said you took apart the first engine and fixed it..............Fixed what?...what was locked up about it?

i took it apart most of it, and tried turning the flywheel till it starts spinning, then try it, but it got stuck so i just put it aside

That makes no sense.......you first said you fixed it and now you say you tried to fix it and then put it aside. Maybe have a real mechanic look at it and help you out.

Are you atleast running your mix 40:1?Check to see if your clutch is hangin up inside the drum.