The throttle cable cannot be pulled too far - you don't say what engine is fitted, but one of the following will apply (most likely first) ;-
1) Govenor linkage physically jammed/stuck/stiff
2) Govenor spring snagged/twisted
3) Govenor spring attachment at throttle control lever bent
4) Govenor vane broken or disconnected (air vane govenor only)
5) Internal mechanical govenor fault
Phil Saunders, March 2009