How To Adjust Automatic Choke

How To Adjust Automatic Choke


The automatic choke is part of your carburetor and is responsible for enrichening the engine upon startup. The choke is there to block incoming air, and assisting the engine in turning over. Once your engine has warmed up properly, the choke plate will no longer be used.

Older carbureted vehicles used a manual choke, which was basically a plate with a long lever attached to it. This lever extended into the cabin, giving drivers the ability to control their choke remotely. Automatic choke mechanisms eventually replaced this archaic design, using a powered servo to open the choke automatically.

Today we’ll be showing you how to adjust automatic choke and resolve any starting issues. Check here if you are looking for other guides on choosing the right carburetor, adjusting idle speed or even a idle mixture How To.

Weber Redline's DCOE Carb - Image courtesy Weber
Weber Redline’s DCOE Carb – Image courtesy Weber

What’s the choke do specifically?


Rather than increasing fuel flow into your venturi, the automatic choke mechanism on your carburetor removes intake of air to enrichen your vehicle. This is vital to the engine starting and warming up, if your choke is not working your car will have problems starting and idling.

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The choke is there because your engine in cold conditions requires more fuel to start and operate. Automatic chokes enjoy benefits that manual chokes do not, such as ease of operation and no chance of leaving the choke closed while driving.

How To Maintain your Automatic Choke


The automatic choke is a very useful part of your carbureted fuel system, but it’s not without it’s own share of problems. Dirt debris and build up can prevent the choke plate shaft or the mechanism that moves it.
Street Demon Carbs have Returned!
Street Demon Carbs have Returned!
Spray your choke plate, and the shaft with a bit of silicone spray at oil-change intervals. This will ensure that your automatic choke and carburetor will serve you well for many years to come. Remove excess build up or debris with compressed air or a can of carburetor cleaner to really get serious.
If you have any questions about the scheduled maintenance of your carburetor, refer to the vehicle’s operator’s manual for proper maintenance schedule.

How To Adjust Automatic Choke

Before you begin our guide on how to adjust automatic choke, you’ve got to figure out what kind of choke is in your car. There’s two different distinct types of automatic choke; a thermostatic spring choke and a thermostatic coil choke.


Make sure to check the orientation of your carburetor housing and the plastic cap of your choke in your owner’s manual before making any adjustments. If your automatic choke checks out according to your manual, and the valve still isn’t closing try turning the thermostatic spring choke to a richer (less air) setting.

To adjust your automatic choke for less air or if it needs adjustment, here are the steps you should follow

  1. Remove the automatic choke screws that hold the cover in place
  2. Rotate the cap until the notch lines up to the indicator on your carburetor housing. Your choke may have RICH or LEAN printed on the outside of the cap.

Adjust your automatic choke until your marks line up. If your car still has problems starting, turn one click towards RICH to see if your starting condition improves. Never rotate more than one click at a time, because making too large of an adjustment can cause confusion.

Demon 625 Carburetors Released!
Demon 625 Carburetors Released!

After you are done adjusting your thermostatic spring choke, tighten the screws to the cover to specification and you are done.

How To Adjust a Thermostatic Coil Choke


The second style of automatic choke is called the thermostatic spring choke. This works in a similar fashion as the thermostatic coil choke, but instead uses a rod to determine engine temperature.

You can identify your automatic choke as a thermostatic spring by the rod that connects to the top of your carburetor. This rod connects to the butterfly valve mounted elsewhere on your vehicle.


If you have not adjusted this automatic choke from the factory, don’t touch it now. Take your vehicle to an experienced mechanic or simply replace your carburetor to resolve your starting issues.

How To Choose a Carburetor


You now know how to adjust automatic choke in your vehicle to resolve any starting issues. Have any questions on our DIY Guide on adjusting automatic chokes? Leave them for us below!