seen a few similar threads to this so forgive me if this is repetitive!
Recently I upgraded my 998 from a single hs2 carb to a single hs4 - along with the stage one kit (manifold, exhaust, needle etc.).
Did a quick little home tune with the gunson colourtune tool and went for a drive and was running sweet as got home to adjust the choke and fine tune a little and the car started to run like dog sh*t. It has a really lumpy idle and rev and im almost certain its only firing on cylinders. #3 being the one that seems to not make a difference if i disconnect while car is running.
leads are providing spark and plugs are pretty new.
Any help would be greatly appreciated. Really hoping this isn't a head gasket.