My rm125 motor took a shit so i got a new one, however the new one i got has very low compression, would low compression not make it start? It kicks over and has spark and every fourth kick it back fires. Should i get new rings and a piston and would this make it start right up?
Yes, low comp will make it hard to start. It has nothing to do with the backfire.
check your air filter, intake, seals, jetting for the backfire problem..