Make the plug for a tight press fit, use Loctite and press it in....
Three Bond 1104 sealer works well, and Permatex Ultra Copper...Permatex is less messy, both seal well...I think the 1104 is what Zenoah puts on the G38 cases.....
Cut both ends off the return spring..It keeps the throttle plate centered in the bore at WOT...Without the spring pressure against the clip on the end of the throttle shaft the plate vibrates and wears out the plate and the carb bore, then it leaks enough to not shut off...