There is no spring on the throttle shaft of an MT-1D. There is a spring on the choke shaft only.
What I do when I install the throttle cable is open the twist grip all the way, slide the barrel clamp on the carb to full throttle, then tighten. This way, you can not overturn the throttle by pulling too hard and bending the throttle shaft or linkage.
Funny story on throttles: One of our most talented members told me his throttle worked backwards, as in you twisted it away from you to increase speed, instead of twisting towards you. I said I had never heard of that, and he told me it was like that when he go it, and the bike was mostly original, so he assumed that is how it went. We were walking around Portland together when we happened along what appeared to me an original, barn find bike of the same year. This bike happened to be next to Wayne's trailer, and the three of us looked at it together. I commented to Wayne that I didn't know that the throttle on these bikes ran backwards. Wayne said they didn't, they were just like all the rest. After we looked at it, we realized the throttle arm was installed on the wrong side of the throttle shaft on the members bike! This was on an MS carb, as the throttle arm is held on by a screw and not a rivet like most MT carbs.
As a side not, the Carpenter carb has a screw holding the throttle arm and can be adjusted to different positions.
