My 7 is running rough. Any Ideas?

Got on my girl yesterday and it didn't feel as good as normal. After that i went to get on the bike (1998 zx7r for those who don't know) to ride to work and noticed immediately that it wasn't sounding healthy, thought it may have just been a cold morning 'thing' but before i even got a few houses up the road i knew it wasn't going well at all. I'm no trained mechanic but here are my thoughts/theorys.
Instead of it's normal running tone it seems to have a gargle. Its repeatative and rhythmic and increases with the revs, and occasionally backfiring which makes me think for some reason only one cylinder is effected. I'm going to begin with a simple attack with carby cleaner but i'm not sure thats the issue seeing as though its backfiring that'd mean fuel isn't having trouble getting in there, right??? its just having trouble with the firing.
Bikes done 41000 k's ish and i'm unsure about when, if at all, spark plugs have been replaced so i might be doing that just because it probably should be done anyway. Also while its up on the stand i'll be doing other servicing. (oil and filter change, collant so on).
Any ideas people??? I'll appreciate all help.
Instead of it's normal running tone it seems to have a gargle. Its repeatative and rhythmic and increases with the revs, and occasionally backfiring which makes me think for some reason only one cylinder is effected. I'm going to begin with a simple attack with carby cleaner but i'm not sure thats the issue seeing as though its backfiring that'd mean fuel isn't having trouble getting in there, right??? its just having trouble with the firing.
Bikes done 41000 k's ish and i'm unsure about when, if at all, spark plugs have been replaced so i might be doing that just because it probably should be done anyway. Also while its up on the stand i'll be doing other servicing. (oil and filter change, collant so on).
Any ideas people??? I'll appreciate all help.