I can't get my toilet to flush properly... PLEASE HELP!!!!!?

Hi,
When I need to flush the loo, the toilet gives a haf hearted gurgle when pulling the lever down and in order to get the toilet to flush fully I have to pump the lever / handle up and down just like an old village water pump!?!?!
I can't figure out what needs fixing?
sometimes even pumping the handle won't work and I then have to flush it by taking lid of cistern and pushing the floater ball down until the bowl flushes itself.
Any ideas would be gratefully received!
Many thanks,
Justin.