vacume leak

[MANIPULATOR]

I am running vm screw top carbs on the 75 TX with stock exhaust. It is idling well with a points ignition that is very old but is popping on the left pipe. A local wrench used an exhaust analizer and informed me the problem was a vacume leak. What could be the source of my problem? bad intake manifold? problem with valves?

 

[CalsXS2]

A lot of times it is in fact the manifol,, or gasket. You can take some carb cleaner a spray around to find the leak.

 

[Amonk]

The intake manifolds often crack overtime without the support of the stock air box.

 

[MANIPULATOR]

Thanks for the tip. These are not stock carburetors, the air box has been removed. I was worried it May be a valve.