Campagnolo compatibility issue!

Hello all,
Struggling a bit with the final part of my road bike build.
Everything's on and everything works fine.. except for gear shifting.
It's a full Campag set-up and although not all the same groupset, it is all of a similar era.
Shifting works fine at the front, but at the back (8spd), the derailleur changes gear in a weird pattern.
ie. On the first change up, nothing will happen, click again and it'll jump two, click again, it'll go up one.
It does just about the same pattern everytime.
I've got v.1 Ergolevers and an Athena rear mech which I would estimate is from about the mid-nineties.
I imagine I wouldn't be having this issue if I was using friction shifters but can't work out what's wrong because obviously, in my mind, the Ergolevers should always pull through the same amount of cable anyway.
It must be the derraileur but I don't really wanna start splashing the cash just yet incase I'm being a moron.
Hope this explains the situation, would appreciate any suggestions!

new inner and outer cables?
could be sticking somewhere?

It sounds like an adjustment problem. Have you fine tuned the derailleur using the cable adjuster?

I iz ashamed son.

Now, Andy might disagree with me, but getting 8 speed Campag to index perfectly needs a lot of patience and even then it soon goes out again. It's a rare day when everything works perfectly.

I'm not going to disagree with you, as you're are right.

Assuming the rear mech is 8-speed and the shifters are definitely 8-speed, then I'd check the cables as always, but just as likely is also the condition of the jockey wheels;

• Are they the correct way round? Upper wheel should be marked "upper" and should have slight lateral play along the bush, but shouldn't be able to angle side to side.
  
  

Other thing to check is that the cable is fastened correctly at the mech and not at a funny angle. See photos online.

Also, what rear block are you using? I assuming 5mm spacing Campag and not 4.8mm Shimano.

Jesus, you guys are good. Thanks for all the suggestions. Going to have a look at it tonight!

ps. Really sorry, Dad!

Other thing to check is that the cable is fastened correctly at the mech and not at a funny angle. See photos online.

This. Fucked me over for ages a long time ago in a galaxy far, far away.