I’ve got a 4 stroke petrol lawnmower that i keep in the shed. I took it out this weekend to do the lawn and after I’d got it reluctantly started it kept trying to cut out, but then catching itself.

What’s up with it? Mucky intake* or something?

*gleaned from a cursory google. I know nothing about four stroke engines.

How long has it been sat with fuel in it and when was it last used? If awhile then probably the carb is gummed up.

Is there a fuel filter?

Turn up the tickover (idle) ….

Governor is just about managing to haul it back from a stall, probably gummy carb affecting fuelling as above. Try carb cleaner spray in the air intake, if that doesn’t work, strip and clean

No expert, mine was labouring under idle to I replaced the diaphram on mine and gave it a quick service, air filter/spark plug and oil change. Only cost me £10-£15 in bits, followed you-tube  and runs like new.

Old fuel, leads to dirty carb.

Strip it down and clean it. Maybe a new plug and air filter too.

Change fuel filter (possibly an inline thing inside the fuel hose at the tank end).

Fresh fuel.

If it still doesn’t run well then your governor springs could be knackered. They’re a pretty delicately balanced set of springs. I did some tinkering with ours to adjust the tension and by gentle persuasion and trial and error I’ve got it running nicely again.

Had our mower been newer it would have got a new set of springs but as it’s sporting the scars of a decade’s hard use I was prepared to fettle!