Aprilia Rs125 extrema wont start/backfires?

I bought a aprilia rs 125 extrema 95 reg. It ticks over but doesnt start, when you push start it on first gear it starts but backfires and sparks come out of the pipe and some sparks from the middle of the bike not sure where from and also does not go even when on full throttle and then cuts out. I added some petrol and oil still nothing?! Any suggestions? Thanks.Well yes ive bought it like this, I put in a twin spark -spark plug and it started but it cut out and later on I started it again and rode it for little but was a bit fussy and sometimes cut out when changing gears. I replaced the old carb, (standard 28ml) to see if this is the problem and still nothing so put back the 34ml and still nothing, the person ive bought it from told me that water got into the petrol causing this problem and I also found some water in the air box so cleaned it out replaced it and still nothing so im thinking of taking the top end apart and see maybe clean it out and see if there is any major problems...any suggestions would be great, thanks, Martin.Oh and ive also checked the spark coil and works perfectly.

I wont ask if it was like this when you purchased, hopefully not.If it backfires that means its sparking to late, which could be electrical (timming or brain not set right) or could be mechanical as in cam chain slipped or broken, bad exhaust valve and more.because you provided so little tech info, its hard to trouble shoot.Best you bring it to someone who knows about bikes in person.