73 Eldorado - port size to balance carbs

[cappisj1]

I added a 73 Eldorado to my ride options. The intakes don’t have ports to balance the carbs. I have gauges that I used to balance my 75 T. What are my nipple options and best way to add them?

[Antietam Classic Cycle]

https://www.thisoldtractor.com/moto_guzzi_loopframe_intake_manifold_modification_to_support_vacuum_balancing.html

[Kiwi_Roy]

The thread is 6mm
If you get a couple of 6mm grease nipples and file the tip of the threaded end the spring and ball will pop out leaving you with a nice hose fitting.
You would also need screws to blank it off later, an "O" ring works as a seal.
Use rubber hose for the first few inches, plastic will get soft and fall off when the manifold gets warm
Having said all that I just use a drill bit to measure the slide opening on my 72 Eldo, I don't believe the balance is that critical.