Whats exactly does it do? is it worth it? pros cons?

thanks again!!

to be honest i think they are a load of old rubbish!!!

they use a different needle and jet and basically overfuel the bike, this does provide a bit more power, but don't ever fit one if the bike is not running right, it will not make it better!!

If you needle jets are worn-out by direct-replacements or use a factory-pro kit (i have never used one but they seem better).

I fitted a dynojet kit to a bike and the jets had visibly ovaled in 2000miles! oh and mpg went from early forties to low 20s.