only advice i could give is
take the securing bolt(s) off, try to remove
if it wont budge pour some cocacola round the base of it
leave it overnight, then fire it up and give it a good hard rev
this sometimes works(done it a few times now)
sounds daft but it is a scientific proven method
something in the coke breaks down the carbon build up and it can soften it up a bit to help it go
might not work, but worth the price of a can of coke to try it