There are several threads in the archives concerning fitting the throttle return springs, and where they go. I’ve not looked at them all, but this one says the rear one (on the 4.2) goes on the manifold bolts, not the carb, to clear the starter motor: Throttle Return Spring Bracket
If this thread doesn’t solve your issue, just search for “throttle return springs #E-Type” and you’ll get quite a few hits.