I have just acquired a 4.5 HP Briggs Push Mower, this thing is like new manufactured in 7/05. The two problems are that when pulling the starter rope it has massive recoil, to the point it will hurt you. Then if I get it to run I have a surging idle at low and high settings. Any suggestions to repair or what to look for?

Viper

Check the flywheel key

exactly, same thing here, check it, its so little the flywheel can be popped off, be gentle on it, the keys are really cheap to replace. did it hit anything abruptly and started doing this?