The cap only goes on one way! To advance or retard timing you have to loosen the distributor clamp. You can't change the timing by moving the cap. Check to make sure the cap is on correctly, as it's possible you may not have it indexed correctly, yet still managed to clamp it down? Also look for possible disconnected/damaged wires at the coil/distributor.
Could you try running the plug wire(s) under the header?
