Seems as though i'm constantly buying new spark plugs for my Murray 2&1 lawnmower. After replacing an old spark plug, the mower runs fine, but after 2 weekends of cutting grass, the mower refuses to start unless i replace the plug. The old plug has a carbon build up on it, but even if cleaned, it fails to start. What could be the problem. Thanks in advance

briggs or tec. flatheads use an autolite 458
which i dont recall a murray 2n1 pushmower using a ohv engine unless its a yardking model with a honda engine

if its old or used alot and i mean alot the rings could need replacing if its really old or used alot. if you are using champions try an autolite. then if it craps out again its most likely the rings. i know one time my mower would start, crap out then when i put another plug in it it would start then crap out after a short while. i replaced the coil and it never did it again which to me was funny but thats what went wrong. but without knowing which engine i can't tell you to check the engine bore for wear. if its a regular flathead side valve its easy to check.