Intake manifold vacuum leak question 72 HO
 

I finally got around to fixing the choke on my 72 HO. While at it I was checking for vacuum leaks with a can of starting fluid.

I noticed #4 port when sprayed on the crossover side increased the engines idle ever so slightly (vacuum leak??). When looking closer it appears the crossover itself has a crack in it. $$$$

Will a crack in the crossover cause a vaccum leak? Im not sure if crossovers have in fact vacuum in them. Could this be as simple as tightening the intake bolts again?? This is a 72 HO manifold with the separate heat crossover.

Comments? Thanks in advance!!

A crack in the crossover will not make for that issue .
Having a cylinder running lean from a leak is not hood so if putting more turns on the bolts doesn't cure it then pull the manifold and make sure the valley pan gasket is not sticking so far out as to be under the over hang of the intake gasket!

Do you have a 72' 455HO with round port heads?

The ports are not fully divided to the intake gasket surface of the heads.

They were done that way to scavenge off another port so that may be causing a lean cylinder.... is yours is that way?

If you exhaust crossover has a crack then you would be leaking exhaust & would hear it.

I had a leak with an intake not fitting just right. I bought and installed a set of ultra seal gaskets( maybe mr gasket ) and was very careful how it went back on. Seemed to do the trick for me. A crack in the cross-over wouldn't cause a vac leak unless the crack extended into the intake port.