Agree with the advise you are getting but did you change plugs and are you using good gas and or treated gas in good fuel lines?
3 things to look at there.
I know some guys will add nitrous to the fuel but that shite is dangerous and can blow up an engine with compression problems.
this is the stupidest thing i have ever seen. nitrous is a gas therefore can not be added to fuel. it would have to be installed with a kit not by just adding it to the fuel.
this is the stupidest thing i have ever seen