need some help with the fuelling

[tobomoto]

i got my bike mot'd last saturday and found that it has trouble revving past 8k.it feels like its restricted somehow. ive got to the conclusion its about 4 or 5 things. these are:-
micron road legal can ;- possibly restricting it
not been rejetted,
k & n filter
me being too fat
carbs need cleaning;- the bike hasnt been used in a while and might need cleaning.
the bike has had engine work done on it. this included porting, polishing, gas flowing and head skimmed. i was also told they were non standard pistons but im unsure exactly what they are. the head gasket was put on wrong previously which could explain if somones changed the pistons. it has a micron full system on it.
ive got it booked in for a dyno run tommorow but would they be able to tell me what it is and if its the jets, what ones i would need? ive just changed the can over to a fuel race oval stubby so im hoping it is just the can. cheers in advance peeps.