Bought it used for $50. Guy said it worked fine last year and even had it serviced, but will not start presently which is why he sold it. Naively I figured likely was a carb issue and I could fix it. B&S engine 124T02 0161 B1. I put in a new spark plug, new coil and new carb. Good spark with spark tester. Checked the exhaust and not obstructed. I checked the compression and it was 50 but also tested the compression on an old Honda lawnmower that starts right away (using same fuel) and also around 50. I took off the valve cover (no oil accumulated under cover) and cleaned around the piston, moves well and not scored. Both intake and exhaust valves move well and head gasket seems fine. Sprayed foam in carb inlet and still no start and got occasional minor backfire. Never comes close to starting. Any suggestions? Hoping not to toss b/c of all the time I put into it. Thanks for any help provided.