Here's some quick tips on starting your petrol mower after it's been sitting over the winter:

E10 and E5 petrol contain ethanol which absorb moisture very easily. If your mower has been sitting in a damp place over the winter months there's a good chance you'll have a layer of ethanol/water mix sitting at the bottom of the fuel. If that is ingested into the cylinders you'll need a new engine.

Empty the carburettor bowl of old fuel and drain the fuel tank and pipes and fill with fresh fuel. Then turn the engine over a few times without the spark plug just in case there is contaminated fuel left in the system.

I know it's a pain but it could save your engine.

Alternatively run your engine on Ethanol free fuel.

Here's a link: https://www.classicfuelsolutions.co.uk/.../classic-fuel...

One last point remember to remove all the old grass from the deck. It can get as hard as concrete and will shred your drive belts!

Andy