I need help with bcs 730 tiller?

i bought a bcs 730 harvester tiller off of criagslist for $700,seller said he hardly used it,when we brought it home we did some late research and found out the tines were worn out to the max.bcs tiller needed clutch adjustment and it was ready to go,meanwhile we ordered new tines we gave the machine some testing,it worked pretty well for worn out tines.4 days later we installed new tines and we did some testing on soil that was already tilled with old tines.the bcs tiller jumps once it hits hard soil.also when the machine jumps and works too much the engine just shuts off.any idea on whats wrong with it?