I have a 11A-B24Z758 190cc 625 Series (2012) mower that stopped working. I originally bought it used at a discount when it wouldn't run. Looking inside there were a few parts missing and to get it to run I rigged up a spring to keep it revved up. It seemed to rev up too high but it worked perfectly for an entire season. If you look at the illustrated parts list on the Murray website it's on page 5. Later on it stopped running completely and won't start at all. When I pull the string everything turns including the blade but it won't even try to crank. I replaced the spark plug and did an oil change but that didn't help and the air filter is clean. Any advice?