Hi, my mate has put a 1.6 cvh engine into his mk3, the problem he's having is when he accelerates past about 2k revs, the revs go mental and jump up and down untile he changes gear, then when the revs get back up again it starts, has anyone got any ideas on what this could be? replaced the plugs, leads, dizzy cap and rotor arm but no improvement.

Cheers