What closes the throttle when you release the grip? The springs there in your photo are typically the governor spring(s) that keep tension on the governor assembly (allows it to function) and does not really work as a throttle return spring. I mean it doesn't look to be a strong enough spring for that. Maybe I am wrong.
Basically what the OP needs here is a push pull mechanism with a stiff enough return spring.
Fig. 26, 29 and 32 deal with remote throttle controls, like mounted on the handle of a garden tiller or edger and where the friction of the throttle lever kept the engine at the desired speed. Is the top spring in Fig. 31 a return spring? Looks like there is a bracket there just to anchor the spring...
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