When the engine on a weed trimmer is tilted, it becomes harder for fuel to reach the carburetor. When the carburetor gets less fuel, it can choke and stall out. In normal operating conditions, fuel should reach the carburetor when the engine is tilted, but a few things can cause a lack of fuel in your carburetor.
Fuel Line Too Short
The quickest and simplest solution to this common problem lies in a fuel line that's too short. The fuel line should extend into the gas tank for about two inches, so it can still suck up gas when the engine is tilted. Replace your fuel line if you find it can't reach the gas when it's tilted.
Dirty Gas Cap
As the engine heats up, the fuel in the tank naturally heats up as well. While some of this pressure is needed to allow fuel to flow to the carburetor, with too much pressure the gas will not be able to flow. A small check valve on the gas cap regulates this pressure, and the extra heat needs to escape out this small hole. You should clean or replace your gas cap if this hole is blocked.
Dirty Fuel Filter
The fuel in the tank must first pass through the fuel filter, which sits inside the tank and is connected to the fuel line. This filter may be clogged on one side, and the fuel may have more difficulty passing through when the engine is tilted in that direction. Replace your fuel filter.
Dirty Gas Tank
Stalling can be caused by debris inside the tank that is clogging the fuel filter when the engine is tipped. Wood chips, grass clippings and dirt can float around in the tank, so you should clean out your gas tank with a little soapy water and a brush if it's dirty.
There may also be a deeper issue in the carburetor. A dirty inlet valve, plugged filters or screens can block a portion of the gas from getting to the carburetor. While a new carburetor can be expensive, installing a carburetor kit may help extend the life of the carburetor. If the problem persists, you will likely need to replace the carburetor.