If there isn't enough bolt sticking out to get a bite on, try a reverse twist drill bit or an ez out set like Damien mentioned. I'd try vise-grips first since that is probably what you have on hand. Next tool you should buy is a torque wrench.
Oh also, there should be an O-ring to seal the carb on the intake manifold. Make sure that is in there. The seal isn't made from being tight (per se) on the manifold pipe, the seal is made between the manifold pipe end / o-ring / carb
Ft lb Torque wrenches really ain't that good under 20 ft lbs
Especially when your trying to tighten a bolt up to 7 ft lbs or 49 inch lbs
I don't think there's a bolt on the CG M/B engine that requires more than 12 ft lbs or 144 inch lbs of torque