I’ve a Mountfield mower which is refusing to run. It’s increasingly needing a jump start but runs ok once running,  starts again etc. now its starting when jumped and idles ok but as soon as you try to pull away it cuts out. battery finally dead?

Dodgy switch probably

Gave up and took the singlespeed out instead.  Dodgy switch?

Carb jet blocked?

Tempting as going out for another ride is…really should mow the lawn. Stumped by this, it starts ok,  idles forever. As soon as you release the break after putting it in gear it cuts out. Would a problem with the carb cause that ?

That’s a blocked carb jet or fuel supply to the carb. Check the needle valve where fuel is admitted to the float chamber.