my 21 has started only firing on the upper cylinder the lower one is intermittent. done all the regular stuff connecters ect (thanks andy) and it was working fine i parked it up had my tea went back out to go to my mates house and its starting firing on one again i pulled the plug out and its wet with petrol its got good spark and compression and fuel (wet plug) and the electrics are fine any ideas what's up with it ?