My mower was surging (probably because of old petrol). Tried three times to strip and clean the carb but didnt solve it. Fitting this took 2 mins (two 10mm bolts) and it’s good as new. I was so close to taking it to the tip, im ashamed to say.
Tip; take a clothes peg so you can temporarily close off the petrol tube as you swap the carbs. Or you could pour petrol over your shoes like me.