OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters stihl fs120

hi i have a question to ask regarding my stihl fs120 brushcutter can anyone tell me the correct way the fuel hoses goes . there is the fuel hose that enters the bottom of the carby .there is 2 hoses a long and the short that go to the primer button does the long one suck the fuel up or is it a drain whilst the small one goes to the top of the carby ? im confused what side of the primer they attach to .hope this is not to dumb of a question. thanks

You can get a free download of the workshop manual here:
http://www.baj.com.ec/files/FR450_-FS120-FS200-FS300-FS350-FS400-FS450-FR350-Service_Manual.pdf

The explanation of the fuel hoses begins on page 40 of 57. Essentially, there are two hoses from the fuel tank. The long hose, which comes out of the tank close to the fuel filler neck, is the vent. The short hose - which has a pickup filter on its end inside the tank - is the fuel supply hose:


The short (fuel supply) hose goes to the elbow low on the carburetor, and the long (vent) hose goes to the elbow high on the carburetor, connected internally to the primer bulb.

I have not found a description of how it works in the manual, but from the way it connects, I think it must be a purge-type system, not a true primer. You pump the bulb as much as you like, and it draws fuel right through the carburetor's fuel side (pumping chamber then metering chamber), and returns it to the fuel tank. You keep pumping until there are no air bubbles passing through the bulb or hose. I rather like that type of system, because they are not affected by too much pumping: the average owner can use it effectively.

That concept of what the primer bulb does, seems to explain what was going on in a previous thread of yours, from more than a year ago.

thanks grumpy your help with the above matter was invaluable really appreciated cheers Bill