predator engine kicking back on crank pull


when cranking a friends kart engine it nearly broke my arm I am thinking he may have changed the cam how big of a cam can you install before losing compression release
even the stock cam will kick if the release is not working . He either took the weights off or they are stuck and not working. he also may have the timing to far advanced
Valve lash could be off, wrong setting will really make it tear your arm off on a bad day