OK, ever since I got my carb rebuilt I get ****ty mileage (230KM using 35 litres).

Before it was rebuilt I got 330KM/35Litres.

Here are my specs (It's non-computer controlled):

Carb: Stock Q-jet, new choke, completely rebuilt to stock specs by a professional (He rebuilt to stock specs he said)
Intake: Edelbrock Performer - just put on so gaskets are good
Exhaust: Headers, 3" exhaust
Ignition: Stock distributor, stock advance, stock (AC Delco) plugs, Accel Coil, Accel Wires
Stock heads, cam, fuel pump, etc....

Cars seems to run PERFECT - idles good, starts right up, no bog when I step on it.

I know nothing about carbs. Nothing at all. What can I do to help mileage?

 

You may have a small vacuum leak. Just cause its new doesn't mean its not leaking.
Check the distributor for proper mechanical and vacuum advance function. Again don't assume its working just cause its "new".
Inspect the whole secondary side of the ignition system for faults.

Check these first before digging into the carb.

 

First thing is make sure the vacuum advance hose is connected to ported vacuum--so you get the extra advance at cruise.

 

The mech/vac. advance is checked by the timing right?

And what is the "secondary side of the ignition system"?

 

I dont suppose you'd be able to tell me where this is?

 

The secondary side is the high voltage side.

Coil, cap, rotor, plugs and wires.

the ported vacuum source for vacuum advance moduates the vacuum advance according to engine load and throttle position.
Typically there is no vacuum a the port when at idle but vacuum increases as the throttle is opened (part throttle cruise)
but load is light or moderate. As load increases (throttle is opened further beyond cruise) this vacuum signal drops off.

Full manifold vacuum port will show a high vacuum reading at idle
and drop some as soon as the throttle is opened some.
Again raising some at cruise as load decreases. it will also drop off as the throttle is further opened beyond cruise to full throttle.
Full manifold vacuum port will show a high vacuum during deceleration when the throttle is closed. Just when it is not needed for vacuum advance.
Ported vacuum will not because the port will show no vacuum when ever the throttle is closed reguardless to rpm or engine load.

 

Follow the hose from the distributer to the carb. Make sure it's hooked up, and that port doesn't have vacuum at idle.