Probably either gas or spark,or lack of.
Take the air-cleaner off. Look down the carb,and pump the accelerator a couple times.
Do you see it getting gas ?
if not,spray some starting fluid in the carb,and turn it over.....Did it start ?
If its not getting gas you could have a bad fuel filter or fuel pump.
Second check for spark. Pull a plug wire off a spark plug. Stick a Phillips screwdriver
in it. Lay on a grounded area. Have someone turn the motor over,while you look for spark.
No spark ? Could be a number of things.
Do these 2 steps,and let us know what you find out.
