how can i fix my mini moto?

my mini moto is really hard 2 pull off the pull cord(which is the band new) i thought the engine might b seized but it wasnt in the end and iv got compression. i no iv got a spark aswell, but i also realised as i was checking 4the spark tht the pull cord pulls fine without the spark plug in. as soon as i put the plug back in it was hard 2 pull agen. any ideas...........