Do I understand carburetor choke?

[DrRoughneck]

My small 4 cycle generator with no primer bulb cannot starts on the 2nd-3rd pull when cold with the choke on. I can immediately take the choke off with no RPM drop.

The folowing is how I understand what happens; is it correct?

With the choke on, pulling the cord creates a vacuum as the piston goes down and the carburetor is obstructed by the choke because the piston tries to draw air in and the choke prevents air from coming in. This vacuum applied to the jets in the carb draws fuel into the fuel lines from the tank. This in fact does what a primer bulb would otherwise do.

 

[bigjl]

Personally I always understood a choke as a way to restrict the amount of air entering the engine, therefore increasing the amount of fuel in the air/fuel mixture.

Hence why if you pull the choke out when driving along on a warm engine black smoke usually comes out the exhaust due to the rich mixture.

I always thought it operated a butterfly valve.

 

[old1]

You are both right!

 

[demarpaint]

Originally Posted By: old1
You are both right!

+1
With regard to opening the choke without rpm drop, that depends on how well the carburetor is dialed in. Sometimes rpms will drop, increase slightly, or stay the same. I noticed a slight increase with my snowblower when I open up the choke.

 

[2oldtommy]

The 4 cycle generator has a very accurate governor that will keep the engine speed in a very narrow range. Of course, the reason for this is the variation and quality of the power output. Any other 4 cycle application may allow for an RPM increase or decrease when the choke is applied. FWIW

Oldtommy

 

[Kawiguy454]

You can call it vacuum but actually the choke plate Lowers pressure in the carb throat. then outside atmospheric pressure can push fuel into that low pressure area.

As far as running goes, the fuel mixture on a generator needs to be power RICH in the RPM range it is set to deliver electric power in. That means once it is started it is more likely to have plenty of fuel with no load. The choke is to add fuel when it is not running yet. you know you should start a generator with no load right ...until it warms up.

 

[Merkava_4]

Quote:
The carburetor has two swiveling valves above and below the venturi. At the top, there's a valve called the choke that regulates how much air can flow in. If the choke is closed, less air flows down through the pipe and the venturi sucks in more fuel, so the engine gets a fuel-rich mixture.