I had the same problem, until Phydeaux showed his formula for distance from the throttle cable shaft. First, find out how much travel you have in your cable, from the pedal up to the pedal down(on the floor). Put that length in this formula:
Radius =Square root of (Cable length measured) divided by 2.
Basically divide the cable length measure by 2 and find the square root of that. And that is the distance you should be around the throttle shaft on the weber. You might find the pre drill holes on the weber are to far, mine were, and you would have to drill in a hole on your own for the proper distance. But this is the way I found I can get WOT all the time on my car.
Also, make sure the cable is pulling in a straight line to prevent binding.
By the way, I found my distance from the throttle shaft is around 2.4 cm or 24mm.
Let me know if you have any questions.