im puting this add on for a friend.... his bike is: Aprilia sr50 1999 70cc malossi kit ( cast iron ) dellorto 17.5mm carb upjetted technigas exhaust standard variator ( 5g rollers ) standard clutch airbox ( dont know what its from ) his bike was running fine until the other day when it suddenly lost power no when he rides the bike kicks in till around 20mph then it loses power and it takes a while to reach 30mph but before it was doing around 50mph any ideas thanks in advance