After following the steps in the Maintenance section, and all other steps in the Tune-up section, now consider the carburetor.
This section covers adjusting the carburetor, rebuilding is covered in the Minor Repair section on the sidebar.
Some carburetors have two adjustment screws, and some, three.
Two Screws:
One is the air/fuel mixture - it is tapered and as it is tightened, restricts the flow of fuel.
The other is the idle speed - it is tapered and moves the throttle.
Three Screws (as above, plus:)
Two are air/fuel - one is for the low-speed, identified by the letter L, usually closest to motor; and the other for high-speed, identified by the letter H, usually closest to air filter.
The third is idle speed.
The air/fuel mixture screw(s) are tapered at the end so that turning them clockwise leans out the engine by restricting fuel flow. Opening, or turning counter clockwise, richens the engine by allowing more fuel to flow.
Adjusting the Carburetor
Run the engine until it is at normal operating temperature.
(continued)
Air/Fuel Screw(s)
For Engines With Only One Air/Fuel Adjustment Screw:
Turn the air/fuel adjustment screw � turn, note the sound of the engine.
Turn the air/fuel adjustment screw � turn the other direction, past the original setting. Repeat this process until the engine sounds best. Open (counter clock wise) the air/fuel adjustment screw a little bit afterwards to allow the engine to run a bit rich; running an engine too lean may damage or destroy it.
For Engines With a Low and High Speed Air/Fuel Adjustment Screw
As above, start with the Low Speed screw. When the engine sounds best, open the throttle and see how it accelerates. If sluggish, readjust.
As above, now adjust the High Speed screw. Test by running wide-open throttle, readjust as needed.
Again, don't forget to open each screw a little bit to be on the safe, rich side.
Idle Screw
After the air/fuel mixture is right, then adjust the idle to the slowest position that allows the engine to continue to run smoothly.
