Carb Performance Knowledge Series. Part 1 "Emulsion Tubes"

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Knowing Your Carbs
Part One
"Emulsion Tubes"
By: Rick Massey

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The Emulsion Tube. Some old-timer’s call it: “Nozzle”. That solid brass tube above the Main Jet, is the most misunderstood part of the Carbs. Ironically, it’s the most vital part for making your bike go – great!

The Emulsion Tube is the main pipeline from the Main FUEL Jet to the Intake air stream. Raw gas passes up through this pipe and goes straight into the Combustion Chamber. If the Emulsion Tube isn’t clean; the performance of your motorcycle suffers and you know it … because you can feel it.

This pipeline is special. There are holes in it. Up to 20 holes on some Models. Both Hitachi and Mikuni Carbs have Emulsion Tubes they are so important.

The (I’m calling it Nozzle, now) … Nozzle is Hour Glass shaped. The middle, narrow section, is drilled straight through with Air Metering Ports. 16 to 24 as mentioned before.

The air surrounding the Ports is supplied via a passage drilled to the Main AIR Jet. This air is the All Important element that helps bring-up the Fuel from the Main Fuel Jet as the Throttle Butterfly’s are opened. And break-up a stream of raw gas so you don’t flood-out!

The surrounding Air enters the Nozzle and is immediately drawn-up into the strong vacuum stream of air drawn into the Intake upon acceleration. The air drags-along some Main Jet Fuel and breaks-up the stream, as the Fuel Passes along the Ports, where the air is coming-in from.

The combined effect of the pin-pointed streams of air, on the diameter of the Nozzle, breaking-up and joining the Fuel, while being further separated and allowed to blend, as the Fuel and Air pass up and around the Needle Valve makes the Fuel supplied to the Intake Stream – atomized! Much closer to being a mist than being a stream of fuel.

As the Throttles are Opened more, the air - captive in the Diaphragm Piston, exits the Diaphragm Piston due to the lower pressure beneath it. This causes the Piston to rise, bringing with it the Needle Valve. As more Nozzle Ports become unblocked by the rising of the Piston Needle; an increased air flow draws-up a greater amount of Fuel.

Should any of the Ports on the Nozzle be clogged with foreign matter; that airflow is negated and the amount of fuel drawn-up is less than needed.

So, consequently, your Mid-range cruising and Top End Acceleration will be affected and the Air~Fuel Ratio needed for peak performance incorrect.

Clean Nozzle Ports and the center pipeline to the Intake is what most neglect to do when cleaning carbs.