ImportRacer1187,
Yes, the S9550 is about 1/2 the height of a standard servo.
penggoy,
I don't have the part number for the spring, but ask any hobby shop for Losi throttle return springs and you'll get these. You get 2 springs and 4 of the mounts.
chuck h & AE Racer,
Yes, according to ROAR rules the carb itself has to have the return device mounted directly to it, but it's not that easy to do on a slide carb. Most guys use a very small elastic pony tail holder (for your hair). That works well, but has to be checked & replaced frequently. I chose this set-up because it was simple & it works well, along with a fail safe. The only way I would have a problem is if the ball cup on the carb popped off (not an uncommon thing, but didn't happen to me all last season). I' ll have a elastic band on it before I run it, or season starts here in 2 weeks.