While a more-accurate diagnosis of carburetor issues may require more time, tools, and patience, there are few simple, quick tests that will help you quickly determine whether your carburetor is performing properly. Grab a buddy—or your eldest child—and perform these time-honored tests to perform a carb-wellness check.
1. Float-level adjustment
With the engine warmed up and idling, remove the air cleaner. Carefully look down the throat of the carburetor at the main nozzle. If it is wet or dripping gasoline, the float level is probably too high. This can cause fuel to discharge from the nozzle while the engine is idling.
2. Idle system
If the engine idles roughly after warming up, the idle system could be at fault. Open the throttle slowly until the engine is running about 3,000 rpm. If the speed doesn’t increase evenly and the engine runs roughly through this speed range, it probably means the idle or main-metering system is defective.
3. Accelerator-pump system
With the float bowl full, the air cleaner removed, and the engine shut off, look down the throat of the carburetor. Open the throttle quickly. You should see the accelerator pump system discharge a squirt of fuel into each primary barrel. The flow should continue for a few seconds after the throttle valve reaches the wide-open throttle position. If not, the accelerator pump system is defective.
4. Main-metering system
With the engine warmed up and running at about 2,000 rpm, slowly cover part of the air horn with a piece of stiff cardboard (not your hand). The engine should speed up slightly as the main (primary) metering system begins to discharge more fuel. If it doesn’t, you may need to re-jet and re-calibrate the system.
Again, more detailed diagnosing, troubleshooting, and tuning will require additional time and attention to carburetor. We have a full library of Carb Tuning and Diagnosis articles in our archives.