Better put that spring back on the throttle arm. With out that spring it will wear out that carb where the shaft goes through the carb.
For throttle servos on my gassers I've been using the solar D770's. They work very well and center very well. If a throttle servo does not center well it's hard to get a the same rpm at an Idle.
I personally like metal gears on gasser throttles as I have a couple of failures over the years. But then again I've been flying since the wright brothers. LOL