How To Check and Set Idle Speed

How To Check and Set Idle Speed


If you are planning on being able to adjust your own carburetor or even tinker with a hot rod project, learning how to check and set idle speed is important. Many times you’ll have to set idle speed to prevent your newer bigger carburetor from choking your engine out, or raising the idle for specific modifications.

Whichever the case, our DIY guide will walk you through and show you how to check and set idle speed no matter what your application. In order to check idle speed, you will require a dwell meter or tachometer at the very least.


If you are not sure what a dwell meter is or how to use one, check our handy How To on using one. Either way, you’ll need one connected to your distributor in order to determine correct ignition parameters.

Connect the red lead to the distributor or your external coil, whichever the case is in your vehicle. Then ground the black lead of the dwell meter in order to use your dwell meter on your distributor. If your vehicle happens to have positive earth, this position will be reversed on your meter connections.


Remove the air cleaner by unscrewing your wing nut and then you are ready to learn how to check idle speed.

  • Raise parking brake and put the car in neutral
  • Start engine and allow it to warm to operating temperature
  • Wait for butterfly valve on choke to open

Using your dwell meter to read the ignition output from your distributor, read the current engine speed and match it against your specifications. If you are running a custom cam and require something else, it’s best to ask your machinist or engine builder for his recommendation.

The next part of our DIY article on idle speed is learning how to adjust your idle. Because you’ve got to know what your idle is before you can set it, this is the second half of how to check and set idle speed article.

There’s three primary components you’ll need to be aware of before you begin learning how to set idle speed.

  • idle speed screw
  • idle air bleed screw
  • idle stop solenoid

The manner in which you’ll be adjusting your idle speed will vary, depending on what your vehicle is equipped with. If you are have idle speed screw you can adjust idle simply by turning the screw to match the desired engine speed, or RPM.


If you have an air bleed screw instead of an idle speed screw, you’ll be screwing it clockwise to decrease the idle, and counterclockwise to increase idle.

Idle stop solenoids will require you to disconnect the solenoid in order to adjust the idle speed. Disconnect the lead from the solenoid and wait for your engine idle speed to drop. This will allow you to adjust to the manufacturer’s specification.

When you are learning how to check and set idle speed, make sure to know what idle you are aiming for. Make sure to plan ahead for any modifications that may require a higher idle or engine speed.

Have any questions about our how to check and set idle speed DIY guide? Please leave them for us below!