Found this website when searching for an answer to a problem with my lawnmower. The engine would start ok and run for 20 seconds or so before spluttering, sometimes backfiring before cutting out. If I tried to cut the grass it would splutter to a stop as soon as it came under load. I was convinced it was fuel starvation.
Stripped the carb down. cleaned jets etc, but everything ok--still same problem. After trawling through lots of sites found this one to be the best.
Found several threads with the same problem, 2 or 3 who had cured the problem with a new spark plug (NGK BPR6ES). Non of these plugs in B&Q so tried my local motor factors. Seems this plug is used in British Leyland cars, cost £1.77 including vat, and it was in stock.
Changed the plug in the lawmower and bingo, as good as new again.
So would recommend anyone with a lawnmower that seems to be suffering fuel starvation to try a new plug first since that is the easiest, and probably cheapest of all options