Petrol lawnmower issues

Hi everyone
I'm hoping someone can help. I have a Mountfield HP474 RM45 lawnmower. It worked great. I gave it a light service, but it has started hunting/surging.

I've replaced the spark plug, governor spring, cleaned the carb and replace all the gaskets. The air filter is clean. But it still hunts.

Any ideas?

 

Dirty old petrol in system from last season, or water in carb bowl, or sounds like you may need to set the idle screws,richness etc again after the cleaning was done.

Did you alter the float bowl screw when cleaning.?

Mine was hunting last month when i refitted my screw to the carb bowl after id drained last years petrol from the bowl. Meddled with that screw and its running good again.

Some fuel cleaner may help also ie seafoam etc.

 

Thanks for the great suggestions. My mower doesn't seem to have idle screws as that was one of the first things I looked for. I had drained my old petrol at the end of last season. I did remove the carb float for cleaning so I'm not sure if I have moved something about with the screws there so will check that again. I'll have to pull it out the shed again this week and play around with it.
Thanks again.