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.

[Superhawk996]

Yes they (vacuum ports) need to be plugged.

Look carefully - should be threaded internally for brass machine screws.

Edit Note: can’t remember which is threaded - Weber or Dellorto. Just looked at DRLA parts diagram and don’t see a blocking screw so you may have to cap them. Threaded screw is much better - doesn’t crack & age and can’t be accidentally blown off by a backfire. YMMV.

Trying to refresh my memory - been a few years since I’ve worked on DRLA.

Looking at part these may work like brake bleeder - see if you can screw it in and it may cut off the passage (replace the o-ring with rebuild kit new part).

You can test this by screwing them in all the way and then blow air or carb cleaner through the port - nothing should come out inside the carb body.

[Osnabruck914]

I agree they should be plugged, but one of them should be feeding the vacuum advance on your distributor. If you are running a purely mechanical advance dizzy, then that does not apply of course, but then you are denying yourself a much smoother acceleration experience. My advice is to utilize that available vacuum!

Osnabruck914

[Jack Standz]

These are 45mm Dellortos, but they work the same as yours.

Plug them. You'll see they go right into the carb below the throttle plate.

[Jack Standz]

Photo

[Jack Standz]

Both fittings in this photo (from the same carb) are crushed on the end.

But they do allow air to bypass the throttle plate. So, plug them with rubber vacuum caps or otherwise.

[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.