Hello, I just joined this morning and this will be a long post, sorry for that. The #'s off of the engine are 126T05-3216-81-10040756. This is my daughters Lawn Boy with this briggs engine. They asked me to look at it with the problem of not staying running. I brought it home and cleaned the carb, same problem. Ordered a new carb, exact same problem. Took the flywheel of and cleaned magnets, installed a new briggs flywheel key. Same problem. Ordered a new ignition, installed it and a new plug, same problem. Installed a new head gasket, same problem. I then lapped the valves, thought one might possibly might be leaking, put it all back together. Exactly the same. It fires when you pull the rope but won't stay running. Open the choke (held open with a screwdriver) it will start but dies after several seconds and never picks up like it is going to run. I read threw 30 pages of posts but didn't see this problem. I don't know what else to try, I'm looking for advice. Thank you I went out and bought her a new mower this morning but I would like to resolve this so I can sell this mower. I drained the fuel and added new, still the same.