Drain the oil and gas first. Before doing any attempts at starting it remove the plug and put some diesel fuel in the cylinder to soften up any scale or rust that may be on the cylinder walls. Let it soak for a day or two . put some new oil in the bottom end then try to turn over the motor. dont want it to start yet just want to make sure you can move the piston . next clean out the carb . if you can get a carb kit now would be a good time to do it as the gaskets will be toast . clean the magneto and see if you can generate a spark. Once you have a good spark (replace the plug maybe even the plug wire). crank the diesel out of the cylinder till it seems dry.load up with fresh gas and try to start it. run it for a short while 10 to 20 minutes and change the oil again . then you should be good to go . Hope this helps and have fun