The primer function on the BR600 backpack blower from Stihl exists to help bring fuel into the carburetor before the engine starts running on its own. Without this primer, the carburetor would not get enough fuel to the combustion chamber to start. The primer on the BR600 sits near the carburetor, on the back side of the blower.
Removing the Primer
Whenever working on the fuel or carburetor systems, always set the choke to "closed" to prevent dust from entering the engine. To access the primer on the BR600, you must remove the air filter cover and air filter, and unscrew the air filter box from the side of the engine. This will allow you to access the carburetor and primer. Disconnect both the fuel hoses from the elbow connectors on the carburetor with your fingers. Unscrew the mounting screws holding the primer bulb to the engine. Remove the primer mount and bulb.
Disassembling the Primer
After removing the primer mount and bulb, firmly push the bulb out of the mount. Inspect the plastic bulb for cracks, damage and signs of yellowing. Replace any damaged primer bulbs, but keep the primer mount for reassembly. Disconnect the fuel hose from the bottom of the primer. Check the fuel hose for any signs of clogs, cracks or yellowing, which may be causing problems in the primer. Replace any damaged or old fuel hoses.
Reinstalling the Primer
When reinstalling the primer back into the BR600 backpack blower, reassemble the parts in reverse order first. Press the primer bulb back into the mount and secure it. Reconnect the fuel hose to the bottom of the primer bulb. Hold the mount and bulb in place while tightening down the mounting screws. Reconnect both fuel hoses to the carburetor. Refit the air filter housing box and the air filter to the side of the engine.
If after removing, inspecting and replacing any damaged primers, the primer still won't pull gas into the carburetor, a more serious problem is occurring in the fuel system. The primer uses pressure just like a running engine, so if the fuel isn't getting pulled into the carburetor, something is causing a loss in pressure. Disassemble the entire fuel system. Clean the fuel tank and replace the fuel filter and fuel hoses. Allow a professional to clean and service the carburetor.