Edit: I just re-read your comment about new hole/weld, good stuff. Below stuff still applies in less binding situations.
I just saw this one, but I had a similar issue on a 670 recently.
Try to lengthen the link bar a little by stretching it out at the bend. When the link is shortened like it is the "angle of attack" is focused near the throttle shaft. Only after enough force is placed on the system will it snap over center and go full throttle. By lengthening the rod a little, the direction of the force is then shifted slightly away from the actual pivot center (throttle shaft) and allows the direction of the force to effectively lengthen the lever arm of the throttle shaft. It's only a small percentage, but that's really all you need.
See the sketch on the right with the 2 lines and the effective arm length (red and black) at the throttle shaft. You'll notice that the black line is slightly longer (better leverage) than the red line.
Without taking all day to sketch and animate this is about the best I can get, lol.
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