Any experts on here - ****ing thing is driving me nuts.

Was fine after first use from winter a few weeks back for an hour and more but the next week started playing up.

Mountfield SP42 2019 basic petrol job, just won't run right.

Little used, petrol clean and fresh, carb clean, jets clear, compression fine, spark lovely, carb linkages all free, safety cut out fine, fuel lines and filter clear etc.

After cleaning it out I remounted without the air filter assembly - it then ran beautifully and re-started perfectly each time.

Put the filter assembly back on and lo and behold won't start - eventually did but conks out quickly.

Logic suggests something has been blocked/moved etc but nothing.

Air filter assembly off, won't start or run again...