fixing stripped carb bolt hole on intake

Helicoil is the only way to go. As you tighten up the bolt the helicoil expands slightly into the surrounding aluminum and the threads can't pull out. If you tapped it out to the next size, there is still the chance that they could pull out again. You can get the kit at NAPA and it includes the correct size drill, tap, installation tool, and 4 to 6 inserts. If it were me I'd helicoil all 4 holes and go with studs.