For the guys out of warranty, maybe someone can open up an EL48 and see what the difference is. It may be something as simple as a different size idle jet or transition hole - which might be easily be altered on an earlier carb.
If someone is going to check out the new carb, there are four things I'd be looking at -
Idle or low speed jet
Transition/air bleed holes
Metering spring
Size of the metering orifice under the needle
Any one or a combination of the above would affect the throttle response.