Carburettors in a two-stroke engine provide the critical function of mixing air and fuel together in proper ratios for the engine combustion. This mixture, when combined and compressed via piston with a spark, ignites and creates the engine energy. Problems can occur, however, when the carburettor malfunctions or is plugged.
Regular Cleaning Required
Not maintaining a carburettor with regular cleaning and changing out of the gaskets can result in old fuel residue gunking up the small channels inside the carburettor assembly. When this happens, the fuel turns gooey and plugs up the flow channels. Then the carburettor cannot mix properly.
If a carburettor's various assembly parts are not secured together tightly with working gaskets, air leaks can develop. If so, additional air beyond the normal intake channels would throw off the mixture inside the carburettor. This in turn would add more air than normal and would cause an engine to run lean (too little gas).
Stripped Fuel Spigot
A common problem due to over-tightening or age is the fuel spigot. Most assemblies secure the fuel line to the carburettor with a spigot that has a bolt going through it. The bolt screws into the carburettor body. If over-tightened, the threads in the aluminium body can strip, causing a loose connection and a fuel leak.