i have an aprilia rs 125 2000,
everytime i try to start the bike by using the electric start button, nothing happens, it seems quite lifeless, however it backfires. if i bump start the bike and can keep it running above 3500rpm shes a beauty, but as soon as i let of the throttle and it drops below, it cuts out straight away and sometimes wont bump start at all afterwards.
i have cleaned the carb, jets, airfilter, airbox, tried using the tick over screw to adjust and different settings on the carb needle. i earthed the spark plug and it seems okay. nothing works!
PLEASE CAN ANYONE HELP?

Trickster019, April 2010

Do you have compression, if not then you will need to have a top end rebuild. I had the same problem as you because my Powervalve Blade snapped and took a couple of piston rings with it and lost all compression.

Richie, December 2010

unfortunately thats a classic symtom of low compression especailly the fact it chuffs out of the exhaust and the fact that it wont tick over.i would say the best thing to do it take the head and barrel off and have a look at the piston and the barrels plating inside as i would imagine its not pretty,also make sure the powervalve isnt broken as this is one of the classic problems of the rotax 122 and 123 engine that they use.you could if you want take the exhaust off and have a look up the port and see if there is any scores on the piston there the exhaust will have to come off either way anyway.

adam bike doctor, April 2010