It very well could do the job, I've not yet tried using this, specific, product. but the 350F melting point is encouraging.
I have worked with other "low temp/multi alloy repair" rods and, while they do work on aluminum, the melting point is wa-a-ay beyond that of the zinc alloy used to cast Keihin carbs. The point...be very careful, start with a sacrificial piece on which you can experiment & perfect your technique. Keihin carb bodies, when heated, go from solid to liquid with the smooth, gradual, transition of...a light switch.
IMHO, for thread repair, better to just source Helicoils.