Yamaha 125 SR - 1st Project

Hello, I have just purchased a 1995 yamaha sr 125 as a project. i knew when i bought it there was an issue with the fact it starts and ticks over, but as soon as you ride it within 5 mins, it starts to loose power. i purchased it at a very good rate from a garage, who say, that given time and lots more of my money for looking at it, they could solve it, however id rather have a go myself. They say, they think its electrical, as the starter swicth on the right side and the horn on the left side have been bypassed and replaced with a couple of ugly buttons on the handle bars.

My plan is to put the bike back to its orginal spec, but I am wondering if there are any points as towards where its best to look, such as coil,cdi (ECU) if this has happned to anyone else, to resolve the loss of power

Heres hoping...

Thanks