The carburettors that come inside a hedge trimmer regulate the air and fuel mixture. This precise mixture must be maintained at all times or performance will be severely limited. While separate, the fuel pumps on these carburettors also tend to warp and wear over several seasons. Due to fuel impurities dirty carburettors need cleaning and servicing every couple of seasons.
Improper Air and Fuel Mixture
The simplest problem to fix is an improper mix of air and fuel inside the mixing chamber on the carburettor, which may cause the engine to shut down. When you depress the trigger, the throttle cable opens the carburettor's valves and allows fuel to mix with the air already present. Even slight disturbances in this mixture will cause noticeable effects on the engine's performance. To solve this problem, restore the carburettor's idle, low- and high-speed adjusting screws to their factory settings. Then make minor adjustments to all three screws to correct for an older carburettor.
Dirty Filters and Jets
The carburettor on hedge trimmers uses a butterfly valve system, which allows the intake and outtake of fuel. Fuel is pumped in via the pressure from the piston's cycle, and excess fuel is routed back into the fuel tank. Inside each of these valves is a small screen that filters out impurities in the fuel. When these filters and the valve get clogged, the mixture will be off. Again, the mixture of fuel must maintain a precise balance. To ensure this, the jets, filters and valves all should be cleaned when the carburettor stops performing.
Over time, or through excessive heating, the diaphragm, which floats inside the fuel pump, will get warped and will no longer regulate the amount of fuel being pumped into the chamber. Maximum power decreases sharply when the diaphragm is warped. Often, the fuel pump must be replaced to solve this problem.
On each end of the carburettor sits a gasket that helps keep an airtight seal on the carburettor. This seal prevents air from leaking into the carburettor and throwing off the air and fuel mixture. With age, these gaskets dry and crack, leading to air leaks. Besides replacing the gaskets, try installing a device that helps extend the life of old carburettors. An inexpensive carburettor kit, often called a "carb kit," sits on the front end of the carburettor and attaches to the intake manifold on the engine. It helps regulate the consistent flow of fuel into the cylinder.