Carb balancing Alpino

[corsaro]

After the rebuild of the 350 Alpino and setting up the running I read the Maintenance manual pages regarding carb tuning.
Removing each of the plug caps in turn to set the slow running seemed to me to be not too good for the ignition system, rather archaic and fiddly .
On my previous laverda 750SF I fitted take off points on the inlet ducts to enable the fitting of vacuum gauge points, so I completed the same for the Alpino.
As the flanges on the inlet tract are quite thin, I made 7mm thick flange plates from alloy insert in the inlet to accept the tappings for the connections
in the photos the tappings are shown on the outside of the bike for clarity but the position could also be on the inside to hide them.
On the SF I connected them after tuning, via a tube ( as shown) to balance the inlets in running.
only extra things to fit were inlet studs 7mm longer.

Now going to carry out the exercise on the 500

Stu

 

[sfcpiet]

Why so complicated?

The little twins have a built-in vacuum take off standard, connected by the black rubber hose in your pic. Remove the hose and connect your favourite vacuum guages, done.

piet

 

[corsaro]

Thanks Piet for the insight, but the hoses vent direct to atmosphere! if they are for vacuum connection why is this not mentioned in the manuals I wonder?
I will investigate further!

Stu

 

[corsaro]

As expected you are correct they are connected to the cold starting channel which indeed enters the body after the slides.
I had assumed they were part of the cold starting system.
Still unsure as to why they were straight to atmosphere as this would allow air into the inlet after the slides creating a weak mixture.
My preference would to to connect the carbs together to aid low rpm balance.
Every day is a schoolday with a new ( to me) old bike
I enjoyed making the redundant parts anyway....
Stu

 

[Paul Marx]

As expected you are correct they are connected to the cold starting channel which indeed enters the body after the slides.
I had assumed they were part of the cold starting system.
Still unsure as to why they were straight to atmosphere as this would allow air into the inlet after the slides creating a weak mixture.
My preference would to to connect the carbs together to aid low rpm balance.
Every day is a schoolday with a new ( to me) old bike
I enjoyed making the redundant parts anyway....
Stu

They should either have a plug or be linked by a rubber tube.

 

[sfcpiet]

I'm very used to finding unexplainable bodges by uninformed/ignorant/just plain stupid (mostly previous) owners. But, funnily enough, there was often a sister-in-law with a brother that knew a guy whos' uncle once owned a car/bike/tractor dealership involved...

I've spent the best part of the last 40-odd years fixing other peoples' well-intentioned mistakes.

Yes, the 2 ports should be connected by a hose, or simply plugged. But the actual "balancing" that might result is largely academic. These ports are also used to balance the carbs with vacuum guages.

Guess you'll be quite surprised over the power gain once the carbs are properly set up!

piet