I have an unknown brand lawn mower with at Tecumsah engine, probably 3 or
3.5 hp. It starts every time, but often runs rough and often stalls, sometimes backfiring before stalling. Sometimes after it stalls, it runs well and strong! One day it was running strong until I bumped it into the mailbox post. Sometimes when runnign rough it sounds like something metal is rattling arouind. Obviously something is moving around. My guess is either it has a sticking valve or the timing gear is jumping due to a loose bearing. I can't find any troubleshooting guides that describe this situation. Any other ideas on hte possible cause? Thanks.Mike D.