Who knows how to adjust them?

My new engine came with an absolutely sinful luxury, a throttle return spring.
Apparently my old engine never had one, (at least in all the years that I owned
it) and the throttle lever always stayed just about where set.

I could easily disconnect the spring from the new engine as well, or I could do
it right and adjust the controls.

I suspect I'm missing a part on the throttle side of the housing. It doesn't
seem proper that the tension spring should be riding against the housing itself
without a terminal fitting.

My current solution, (jamming a screw driver behind the throttle lever to hold
it in position under way), is way to lubberly to put up with long term.

If somebody knows how to adjust these levers, great! (I've already unscrewed
the
top plate and tinked around with the screws below.......no results). Otherwise,
that throttle return spring is headed into the spares box.