Follow these steps to check your carburetor：
1. Check the Air Filter
Make sure that the air coming into the carburetor is clean and free of debris by inspecting the air filter. A clogged air filter is a common cause for black smoke emitting from the exhaust.
2. Check the Connections
The connections attached to the carburetors’ throttle and choke plates can bind or stick when dirty. Constant vibration and wear can affect the setting of the carburetor’s mixture screws.
3. Use carburetor cleaner to remove deposits, clogs & debris
With all of the grass, twigs and other debris that a small engine encounters, it’s not surprising that even passages inside the carburetor eventually pay a price. Deposits inside the carburetor can clog fuel and air passages and reduce performance or stop the engine altogether.
Luckily, you can take care of many of these problems quickly and easily, often without even removing the carburetor from the engine. Commercially available carburetor cleaner comes in convenient spray cans for periodic cleaning of both inside and outside the carburetor.
In addition to cleaning the carburetor, many engine performance problems can be linked to maintenance issues such as stale fuel, dirty air filter, fouled spark plug, and deteriorated oil. A great way to help avoid these problems would be to perform an annual tune-up.
Watch the video about cleaning carburetor for help if you need.