Kit Carb Question - Should be an easy one for you ol' timers. 😁

[yuckfoo]

What is the long hexagonal piece that the jet screws into? (It's also what the needle goes down into.) Is it technically a "jet" of some sort? If so, what part of the throttle range does it affect? Can I buy different sizes, etc., etc.

 

[DAMIEN1307]

What is the long hexagonal piece that the jet screws into? (It's also what the needle goes down into.) Is it technically a "jet" of some sort? If so, what part of the throttle range does it affect? Can I buy different sizes, etc., etc.

Technically speaking, they are called "emulsion tubes"

I'll try to make this simple so here goes...lol.

The basic theory behind it is that the emulsion tube in a carburetor is used to maintain the air/fuel ratio at all speeds.
It consists of a well with main metering jet at its bottom.The jet has holes on its sides. It is in "balance" with atmospheric air.

Initially air is drawn through the holes into the well and gasoline is emulsified.
When the throttle valve is opened, the reduced throat pressure causes the gasoline to emulsify and mixes with incoming air and reducess the richness of the mixture. As speed increases, the holes in the central tube are progressively uncovered, thus maintaining air/fuel ratio....DAMIEN

 

[Cisco]

they are called "emulsion tubes"

Thanks for that. I didn't know the term.

It is in "balance" with atmospheric air.

Interesting point. Carburetors work on the venturi effect. Fuel isn't sucked in, it is pushed.

what part of the throttle range does it affect?

The slide needle is tapered, so as it is raised up, the area of the venturi opening increases. This works to meter fuel up to about 2/3rds or 3/4ths throttle. After that, the needle has little effect, and it is up to the main jet to meter the fuel.

Can I buy different sizes, etc., etc.

There is little that can be changed in these NT type carbs. Float level, main jet, and needle position are the only adjustment options.

RFC, please correct me where I am wrong ;-)

 

[DieselTech]

I believe you can buy different needles, with different shapes/tip profiles to really fine tune things if you want to spend the time doing it. Alot of engine tuners will shape there own needle to fine tune it perfectly for there particular riding styles.

 

[Deeman69]

Damien's explanation was good. I would add that emulsifying the fuel also breaks its surface tension so that it flows easier.

 

[Axl Myk]

I always called it a gas sucker upper tube.