2000 Citroen Saxo

car will start from cold ok, but once engine is hot starting is difficult, it is spluttering to go then revs itself, stong smell of petrol. white film on under side of oil filler cap and a bit of water inside, but no water on dipstick. was told this is because we are doing short trips, so ive changed oil and filter but almost straight away same day white film on underside of filler cap even though i took rocker cover off and clean it all first. ive changed the carb and air regulator but no different, still after first start up ok then switch off and start again and it struggles.

thanks

mat