How a choke in a carburettor works....explanation! : Suzuki GSX-R Motorcycle Forums: Gixxer.com

**Armi** · 11-12-2012, 04:08 AM

Actually i'm looking for one?

After that thread...cam't find it, I owed an explanation, as to how it works.

Have done some reading and am abit confused.

Read in one tuturiol that when it's cold, fuel sticks to the cylinder walls and therefore requires MORE fuel to start the bike....didn't say how it provides the extra fuel?!?!?!

In another tutorial, it says that the choke opens an air circuit and runs the engine at a higher rpm, which is totally contradictary to what was said above?

Whats a throttle valve?....that's the slide, right?

**dj_smurph** · 11-12-2012, 06:13 AM

Throttle valve is the butterfly. The slide metres the fuel. The choke I think moves a butterfly that changes the air pressure difference across the carb and enrichens the air/fuel mix. How it does it I don't know

**TheGeek** · 11-12-2012, 07:13 AM

Throttle plate is below the jets. It doesn't change any pressures, only air velociy at the jet which is the venturi effect vacuum. The choke is above the jet. Closing it applies a direct vacuum at the jet increasing the fuel.

This is in the simplest terms. It can get much more complicated.

**ccmhunt** · 11-12-2012, 07:40 AM

In your Mikuni CV'S this>> In another tutorial, it says that the choke opens an air circuit and runs the engine at a higher rpm,
Remember, I told you that the choke plunger opened an air passage from above the piston diaphragm to the upper venturi on the engine side of the butterfly . This was the direct effect.
Now, what is the indirect effect?

**dj_smurph** · 11-12-2012, 08:33 AM

The idirect effect is it lifts the slide more increasing the amount of fuel while keeping the amount of air the same enrichening the mix

**THE SRADIATOR** · 11-12-2012, 08:37 AM

I know this one...Less air ='s More fuel?

**THE SRADIATOR** · 11-12-2012, 08:40 AM

Quote:

Originally Posted by TheGeek

Throttle plate is below the jets. It doesn't change any pressures, only air velociy at the jet which is the venturi effect vacuum. The choke is above the jet. Closing it applies a direct vacuum at the jet increasing the fuel.

This is in the simplest terms. It can get much more complicated.

Any time someone whips out the word "Venturi" you know it's going to get complicated!
Although...for some, the word "Floats" has complications and a life all their own!

**Armi** · 11-12-2012, 08:46 AM

I know what the venturi is.
If the choke plunger opens an passage above the piston diaphram, this will in turn lift the needle, allowing more fuel in,no?
I mean the slide, slides up the needle, allowing more fuel.

Can someone put up a correct diagram of whats going on?

**TheGeek** · 11-12-2012, 09:13 AM

Then that's not a choke... it's an enrichment mechanism.

Moto_Joe · 11-12-2012, 09:37 AM

The real confusion comes in that choke enrichener and fast idle are all incorrectly used as if they are interchangeable only because they are used to achieve the same desired effect.

There are tons of things that are like this too.

Backfire/after fire
Flooding/gas fouling
Etc.

**Iloveurmommy** · 11-12-2012, 10:26 AM

This is probably one of the best guides IMO to understanding carbs. I know it helped me a great deal.

http://dl.dropbox.com/u/106752/Manua...etion_1975.pdf

Here is the thread I found it in:

http://www.thegsresources.com/_forum...ighlight=Great

Enjoy!!!

Sent from my iPhone using Motorcycle.com Free App

**TT750** · 11-12-2012, 12:16 PM

cold fuel doesnt atomize well..

wish this showed a air choke like on the srad. instead the choke valve actually opens a port to let more fuel where in our carbs the choke valves lets vacuum travel to the diaphram and lift the slide and needle to let more fuel.

You Tube

when you look at srad carbs and many others you will see the choke valve on the top of them. basically the direct opposite position then the video. because you want vacuum to be directed to the top side of the diaphram. when you pull the choke you open the port in the top of the bore on the engine side of the butterfly to let vacuum up to the top of the diaphram lifting the slide and needle.

**TT750** · 11-12-2012, 12:22 PM

in this video you can see the fuel being atomized into tiny droplets as it comes out the main jet kinda cool

You Tube

**ccmhunt** · 11-12-2012, 12:58 PM

So after all the hints, we have a conclusion, the choke is an air mechanism, whose secondary function is to raise rpm and meter more fuel.
That's the distinction I was driving for, because all too often there is a misconception that there is a choke jet, or that the choke itself is metering fuel. So my questions in the other thread, that asked you all the ponder it, and gave you all the information that the mechanism opened the passage from venturi to chamber above diaphragm, was merely an exercise to make you arrive at a forgone conclusion and to remove the misconception of a choke fuel jet mechanism in our carbs.

**Apok** · 11-12-2012, 01:17 PM

You bastage, both of my answers pertained to that.

**THE SRADIATOR** · 11-12-2012, 01:20 PM

When he whips out the word "Venturi" from his vocabulary tool box, things are gonna get serious right quick round here! (I hate when things get serious as it goes against everything I stand for!)

**THE SRADIATOR** · 11-12-2012, 01:22 PM

Quote:

Originally Posted by TT750

cold fuel doesnt atomize well..

wish this showed a air choke like on the srad. instead the choke valve actually opens a port to let more fuel where in our carbs the choke valves lets vacuum travel to the diaphram and lift the slide and needle to let more fuel.

http://www.youtube.com/watch?v=wyspAHrMbb8

when you look at srad carbs and many others you will see the choke valve on the top of them. basically the direct opposite position then the video. because you want vacuum to be directed to the top side of the diaphram. when you pull the choke you open the port in the top of the bore on the engine side of the butterfly to let vacuum up to the top of the diaphram lifting the slide and needle.

Ohhhhhhh...pretty colors!
See pretty...

**dj_smurph** · 11-12-2012, 01:30 PM

https://www.youtube.com/watch?v=APq5...e_gdata_player

This shows mjn kit working as well as fuel atomising

**TwistedMister** · 11-12-2012, 07:23 PM

Quote:

Originally Posted by Armi

In another tutorial, it says that the choke opens an air circuit and runs the engine at a higher rpm, which is totally contradictory to what was said above?

he said, it adds more air, he also said that in another thread a while back when I was going through my carbs when I thought fuel may be leaking out the choke o-rings..

he said "remember the choke adds more air"

I fear you blonds aren't going to do so well on the test...

**TwistedMister** · 11-12-2012, 07:26 PM

Quote:

Originally Posted by dj_smurph

https://www.youtube.com/watch?v=APq5...e_gdata_player

This shows mjn kit working as well as fuel atomizing

is that the perforated needle set up?

like to get me a good set of spares and try those some day, prolly when I hit the lotto..