The Baja Heat mini bike has a 200cc 6.5 Hp size engine.
Homelite
gas
Castroil
A 2.8 = 97cc
monsterscooter parts has them on the internet for $42
It's not easy to do.
Buy a new one.
Go towww.bajamotorsports.net for complete owners manual.
There's an adjustment nut on the hand grip for the throttle cable. Back it out to make the throttle tighter, and screw it in for looser.
http://jleibovitch.tripod.com/id247.htm
To way to fix that ... eiter change the oil or your ckoke may be broken I have the same bike and that was the way i fixed it.