When you take the lid off the top (it's held on by 3 flat-blade screws) there are two arms inside that pivot around an axis and they have screw adjusters on them to dictate when the accelerator pump engages. It is ABSOLUTELY CRUCIAL that those are adjusted properly or you will have a terrible flat spot, as you noted. It took me many trial runs down the road with that little lid off and making periodic adjustments to get it just right. I mentioned this in your other thread, but you really need a manual, like Chilton's, to be able to adjust it properly because it shows some pictures. They're only about $13, but well worth that if you do your own work.
Currently an '86 CJ-7 and a '77 CJ-7 Golden Eagle---#4 and 5 following a '01 Sahara, '90 Sahara, and '85 CJ-7....