on the odd occasion the bike sounds like its not firing on all four so after a few hours of fun changing the plugs(with a lot of help from a more experianced chap from work) which the old ones didnt look too bad afterwoods took it for a little ride stopped for a min fired it up and the sound came back again but went back to normal after a minute where as before the plu change the sound was sort of there everytime i started it up when the engine was warm and normally at idle(not the cct) i was wondering if anyone has had this problem and advice given will be a great help as i seem to have chosen the wrong carrer with the price for labour the bike shops charge

 

I would look at the carburetors and fuel lines, you may have a stuck float or pinched hose.

Run the engine up to operating temperature and shoot a mist of water at the exhaust header, if any of the pipes stay wet that will indicate which cylinders are not firing.