I was pulling off my Holley carburator, and the bottom of the carburator, (connects the carb to the manifold with the vacuum ports on it) cracked right off.

Before i spend money and try to get a new one from holley, I was wondering if JB weld might be a good idea to try? I figure it it doesn't hold then i'll be right back where i started, and if it doesn't then i dont have to worry about it.

Does JB weld have a good bond with Aluminem?

Worth a try, I use Jb weld for lots of things. If its just an ear where one mounting bolt goes, be careful tightening it down next time.

I guess it won't hurt to try. I SERIOUSLY doubt it will work. The bottom surface needs to be perfectly flat (that's why it is machined). If not you will have a vacuum leak. I wouldn't waste time trying to "glue" it. JB Weld is basically epoxy, it's great for some things but, I won't think this is the place for it. Even welding a base plate is not a great idea (unless you have a mill to surface the whole underside of it). For the price I would just buy a new one.

Typical reasons for the base plate to crack or break are, double gaskets, uneven surface, over tightening, not alternating as you tighten. The base plate is not flexible at all.

Depending on the model carb you might be able to find a used for cheap (E-bay, swap meet, friends). It is simple to replace.

Epoxies like JB weld will not hold, been there with many customers, the only fix is to have it welded $30.00 and then resurface plate. New ones are very spendy!!

A repair with JB WELD probably won't work. That's a problem with HOLLEY or EDELBROCK mounting ears. It's due to the porosity of the cast aluminum. Luckily, it doesn't happen that often.
The EBAY suggestion is good if you need to fix the problem cheaply. There's plenty of carburetors for sale. BUYER BEWARE.
You might be able to use an aftermarket solid billet base plate from PROFORM...check SUMMIT RACING or JEG'S for applications.
You might want to contact BARRY GRANT/DEMON and give them your motor specs. They'll have a DEMON carburetor that might be just the ticket. They base plates are also billet for just this reason.
Over torquing the base plate nuts or not checking to make sure that the carburetor is sitting square on the manifold is a possible reason why the mounting ear broke off.