Rev counter goes up but speed does not

sounds like your clutch is slipping and may need replacing

Is the clutch cable operated? If so, make sure the cable's not too tight. Might be self-adjusting but still worth checking. When pressing clutch pedal, need some free movement before it starts doing anything. Same applies to hydraulic operation. If the release lever can't come fully back, with some play, clutch will slip and if it's not already worn it soon will be! Note that the play disappears as the clutch wears, and must be adjusted for (automatically or otherwise, depending on the car).