How do i Rebuild or find part or unknown engine

ok am having problems with my go kart its a 5.0 hp , i dont want to start now, wen i first got it to start it maintained on idie and moved really slow.
what can i go to make my kart move fast then on idie speed lol.also wen i try 2 pull start it , it gets stuck and dont move ...... if i try 2 pill hard i know ill mess it up .
pix of my kart coming soon
please and thank you for you help

also i want to know how can i rebuild my enging becuase its kicking out fire out the exhaust