Dellorto Carbburetors., Am I missing something? Options

[Petepat]

So I'm just overhauling my carbs on my 1.7 engine and looking closer with them out I notice there are 2 small pipes, not apparently doing anything by letting air into the manifold!! Question should these have caps on them? I get a lot of pop and bangs from the exhaust.

[porschetub]

So I'm just overhauling my carbs on my 1.7 engine and looking closer with them out I notice there are 2 small pipes, not apparently doing anything by letting air into the manifold!! Question should these have caps on them? I get a lot of pop and bangs from the exhaust.

They are designed to fit to an old fashion "manometer " ,Delloto's way of assisting with throat balancing but redundant if using a STE synchrometer ,I have the german made Redline type and there is none better IMO .
Can't remember exactly but the LH side carb has the vacuum tube for an SVDA type dizzy ,the other side has no vacuum stand pipe as not needed ,one carb will supply enough vacuum for " 205" series distributors in in good condition.
If you have popping @ the exhaust you need to check the size if the main jets and check you have no inlet vacuum leaks or a leaking exhaust for example .
Not sure what carb specs you have but my last customer build 1.8 had the following ;
28mm vents,
52 idles jets,
130 main jets ,
as supplied air correctors and emulation tubes.
2 psi fuel pressure .
Those vacuum test ports have a sealing "o" ring so make sure that is changed .
IMO these are great carbs and if clean they are very easy to tune with the correct jetting ,cheers.