Model:HRR2166VKA, bought at HD 1 year ago. Was "factory reconditioned" though it appeared new to me when I bought it. No issue in year 1. Mower very easy to start in fact. I estimate about 50 hours of usage in year 1. Mower outside for the winter but away from elements. This year: used the mower three times with no problem. During the 4th mowing session, the mower died as I was mowing. Checked for gas, no problem. Restarted after three pulls. Died while running again about 10 minutes later. Has not restarted since and that was 4 weeks ago. Changed spark plug. No effect. Old spark plug was dark. Changed ignition coil. No effect. Examined carburetor: looks clean, blew compressed air through bottom hole and seemed to flow fine. Reinstalled and no effect. If I take the spark plug out and leave it outside while I pull the cord, I don't see a spark. Am I supposed to? When I take the spark plug out, I can smell fuel. The air filter is clean. I tried starting it with air filter out. No effect other than sound change. When I changed the ignition coil, I got a tiny bit of white smoke out but it only did it twice. Otherwise, there is no smoke coming from exhaust and no corresponding "explosion" in the piston though you can hear the motor moving as a result of starter pull. No backfiring of any kind. The same fuel runs fine in another mower and I checked the oil, there is plenty and it is clear. I have not squirted gas in carburetor and tried to start but I did notice that there was fuel in it when I removed the bottom screw and that the flow was unimpeded going through the jet. I also took out the kill switch by disconnecting from the coil (both old and new). No effect. I love this mower but I am at a loss. Thanks in advance for any help.

I have a 20 hp briggs that just began backfiring when I started it. Once started it ran fine. Now it has begun to backfire and stall when under a load. If I disengage the mower it runs fine, but when I put it back under a load it will backfire and stall. Any ideas?