Vacuum pressure dropping on idle

[GaryM]

Thanks for your help.

 

[dannyk]

The restriction in the 'T' piece is to stop the sudden change is pessure from shocking the gauge. If you stick in a 'T' piece with no restriction them you may damage your bourdon tube inside and it'll be out of calibration.

 

[GaryM]

That seems like a more credible reason to source the correct T piece complete with restrictor or stick with the plastic item.