I have no idea what you are talking about, Jamie.
We have run multiple classes, multiple engines, etc (especially on the champ karts.)
I've never had a set screw come loose on it's own. Are we talking about the same throttle linkage system?
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The little set screws simply flatten out the cable so that it won't fit back through the hole on it's own. Just run it down snug.
If you loosen the set screw and try to adjust the cable that way, chances are that you won't get the cable back in right once the spiral windings of the cable are flattened out.
The nice thing about this system is that you can change motors without having to move the cable and set screw. Set it and forget it.
Most Euro and sprint chassis are set-up to use a single cable from the pedal to the carb.
That's alright too, but then you deal with some cable stretch (especially with some of the cheap import cable that's being sold) plus this linkage makes changing engines much simpler.