Flat spots/ loss of power

Hi my 1.8 clipper has just started misfiring on the way home from work. Up until now apart from the inlet flange needing replacing its been very good all of a sudden it started lurching and almost stalling when pulling away. Any ideas on how to fix this?

Over the moon..I checked the distributor and the four points were pretty fluffy. Carbon? cleaned them back to shiny, and shes running well again now  

My old carb engine did this once. Was water in dizzy, expansion hose had split.

Any misfiring I'd check leads and cap first off every time.