How to Adjust a Motorcycle Carburetor

A motorcycle carburetor, being a key component in a motorcycle, must at times be adjusted to deliver the right mixture of fuel and air to the bike's cylinder. If this mixture is not set correctly, it can affect the operational efficiency of the motorcycle. This, in turn, can increase the bike's fuel consumption and can reduce its power. This setting adjustment is relatively simple and as a motorcycle owner, you should be able to adjust your own bike's carburetor setting when you see a need.

Things you'll need:

  • Clean cloth
  • Carburetor cleaner
  • Engine RPM gauge
  • Screwdriver

Step 1 – Remove Dirt, Debris, and Oil Deposits

Locate your bike's carburetor and spray its outer surfaces with carburetor cleaner to dissolve any oil deposits that have built up over time and may be interfering with the efficient operation of your bike carburetor's moving parts. Use a clean rag to wipe away these deposits, along with any dirt, dust, or debris that might be imbedded in them. If necessary, spray additional amounts of this cleaner, then wipe the surface with a clean part of your rag until all deposits, excess cleaner, oils, and grease have been removed. 

Step 2 – Check Your Carburetor Fuel-Air Mixture

Start your bike and let it run. When the engine is warm, locate the fuel-air mixture screw. Usually you'll find this adjustment screw on the carburetor barrel's side, three or four inches down from the carburetor barrel's top edge. Attach your RPM gauge to the carburetor by first detaching the bike's vacuum hose. When the bike is running at a high idle, check the RPM gauge. If the RPM reads less than 1400, use a screwdriver and turn the mixture screw in a clockwise direction, keeping an eye on the RPM gauge. Stop turning the screw when the gauge shows an RPM of 1400.

Step 3 - Adjust Your Mixture Screw Setting

Your bike's RPM rate when the bike's engine is idling at a normal rate should be at the 1000 to 1100 RPM range. To get this RPM when your bike is at a normal idle and the RPM is higher than the normal range, turn the mixture screw in a counterclockwise rotation. At a point when you hear the engine begin cutting out, back the screw slightly until the engine is running smoothly again. The RPM range should now be between 1000 and 1100.

Step 4 – Final Mixture Screw Setting Check and Adjustment.

The final test for the bike's correct fuel-air mixture should now be made. From the carburetor, remove the RPM gauge and attach the carburetor's vacuum hose you removed earlier. Have your bike's engine running at a normal idle. If you hear, or feel, any irregular firing of the bike's cylinder, turn the screw slightly clockwise until the engine is running more smoothly. Then, re-attach the RPM gauge and check its reading. If it is showing an RPM in the lower range (near the 1000 RPM mark) adjust the mixture screw until the RPM is closer to the 1100 mark. Finally, remove the RPM gauge and reconnect the vacuum hose.