Did you put ina new plug or just clean the old one? If you didn't get a brand new plug and try it. Make sure you valve clearances are good also.

 

Is it brand new? What year?

 

alright this might not be the problem but, if you got a new airfilter or recently moved the old stock one, then you better make sure that oh so important green wire is grounded into that hole by a bolt or something metal, mine did exactly what you are talking about and i did everything everyone listed up there. I couldnt believe that that little green wire held down by a bolt was the problem. So just tighten the bolt and see if that works.

Goodluck