Hello All, I sole owner of a 1998 JX75 John Deere walk behind mower. This mower has served me well for over 20 years. Now it has issues. It starts cold like normal and runs for about a minute. Then it shuts itself off. It’s impossible to start afterwards but it gives false hope to keep me pulling on that rope: it pathetically runs on without throttling up, and when it doesn’t do that, it backfires through the carb. I suspect dirty carb causing lean burn. I have cleaned it three times. Each time the mower starts and runs well until I am finished mowing and turn it off. Next time I go do use it, I repeat the process. Symptoms point to lean, but I am stumped. Help (please)!