I just started using TT after many years and it is skipping even though the records aren't warped.  The arm moves ok vertically but the cart doesn't track well. Does anyone know if there is a way to adjust the cartridge arm tracking force? I have the original MMC3 cart and it seems to work ok except for the skips.   

Tracking weight is adjusted via a slider which can be seen between the two arms and is adjusted from under the playing arm.

Should be set to 1.2g

It may be that your stylus is u/s or the suspension in the cartridge has gone hard after some years of non use?