DP secondaries

Ok, So I think I have learned by now, to ask a question first. Before I go messing around and making something simple into something complicated.

I have a mechanical secondary holley double pumper on my 340 and it is running great. Choke is set up good car starts and drives great.

So today I have a friend in the car push the pedal to the floor and an look down the carb, the secondaires only opend about 3/4 of the way.

Whats the best way to go about adjusting them. Tighten the throttle cable? there is a very little bit of slack in the cable...

or is there any adjustment to get them opening up a little sooner?

Thanks for any pointers..

Shane