Emusion tubes - the deepest dark secrets of Webers

Fuel and air jet control mixture from the time the main venturi come on line until the peak airflow at WOT.

The trick with emulsion tubes is that they control the delivery through the midrange. The holes drilled in the ETs are positioned carefully to blend the harmonics of the inlet tract, the cam overlap, and the header harmonics with the total mixture requirements of the motor. So when the harmonics are moving a little more air, the emulsion tube adds a little more gas(hole), when the harmonics are pushing air backwards, the ETs reduce gas (lack of hole), all smoothing out the powerband.

From a thinking perspective you need to think of the ET as being upside down. Filled with gas when there is little air flow and filled with air at max airflow. A side benefit of emulsion tubes is that the gas starts to vaporize due to the air flowing through the holes before the premixture gets to the feader venturi.

I don't know how to directly specify them, but to it is fairly obvious when the tubes are ok, right on, and flat wrong. Since the mixture is controlled with the main and air jets, the emulsion tube is fintuning the mixture across the engine breathing characteristics. With a weber dealer, we used to obtain a 6-8 complete sets, and play with the carbs until the engine came to life, and give back the ones that weren't right (1970). If you are using a standard Ferrari head and intake port, cam and header, use the standard emulsion tube. Otherwise, be prepaired to experiment.

 

Russ
The Weber carb book (available from Pierce) gives a pretty good description of the operations but also has the sequencing and sizes of all the ETs.

 

I owned a 1973 Toyota corolla on which I put two sidedraft 40DCOE's.
Bought the car new for 2800$. No Typo, I'm old.
Anyways two tricks.
Buy a set of metric drill bits real small.
The jets are (were) made of brass which you can solder over then drill holes into. When you figure out which jet works well for you, order the correct ones and discard the soldered jets.
To figure out rich/lean we use to perform "plug cuts" where we would run at @6000 rpm and shut the engine off, coast to a stop and check the condition of the plugs. You can do this for all the RPM range.
Of course this was a great reason to go fast and we went to college in a dry county in Ohio so it was a reason to make a 16 mile beer run. I did get it lean once and had a detonation which bent a rod, but that was another reason to go into town at high speed!

 

Russ
I'm told the idle jet impacts the entire range with very small throttle openings.
Philip