cracking carb bodies?

[lmalone]

so I have a 1968 plymouth valiant 2dr...anyhow it had not been run in like 8 yrs...anyhow decided to get her up and running. Did the usual plugs, wires, oil, new gas tank filters etc... anyhow after the carb was rebuilt I bolted her down to the manifold and she would run fine at idle but not in gear. So I figured vacuum leak...so I found one, a nice crack in the carb on the drivers side just above were it bolts down...so that sucks, but I figured it was just an old bad carb. Next I take a carb out of my 1972 scamp and decide to bolt it one to see if she will make it around the block, still same issue so again I start looking for vacuum leak and guess what...this carb has developed a crack in almost the same spot...wtf??? the only difference I can see is the intake manifold doesn't have the usual studs to put the carb down on so I used 2 bolts...instead. is it possible that is my issue or do you think the intake is warped enough to cause this???? 2 good carbs are now crap...and I never see these at any swap meets...
they were both holley 1920's
Thoughts...

 

[GeorgeH]

overtorqueing

 

[lmalone]

Thats just it I didn't even tighten it down that hard... never had this problem on any of my other 3 slant sixes just this one...

 

[Dubob]

I'd be laying a straight edge across the mount pad for the carb, I believe you'll find it to be warped.

 

[lmalone]

Will definately being doing that and ebaying 2 new carbs now..