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

hi to all. maybe someone has had this problem before. I have a stihl fs120 brushcutter that is hard to start after the first time even thats starting to change , I have changed the barrell and piston, carby , seals etc all new parts except the clutch. My problem is the damm thing is difficult to start . I try to start it with no choke no priming as it is hot or choke, no prime, it does not seem to matter . im getting sick of pulling my guts out to get it to fire maybe its flooding or maybe its not getting any fuel . any help would be appreciated. cheers

We need to get more information, bill.

First, let's talk basics. Here is how you are supposed to start it:


This does not sound exactly like what you said you have been doing. First, you have not confirmed that you have been setting the throttle to the start position, for both cold starts and hot starts. You would be very lucky to get the engine to start if you do not do that. Second, you have not been priming it to hot start it, but as I read the instructions, Stihl says you have to (which surprises me considerably - I've never done such a thing as prime a hot engine, but it is at least one of the things you need to try). Now, after doing exactly what Stihl says you should do:

1. Does it start easily from cold?

2. Does it do warm restarts easily?

3. Does it have a new spark plug?

4. Have you tried loosening the fuel cap, in case it is not venting properly?

Grumpy, thanks for your detailed instructions, I should have explained I have had this trimmer for at least 10 years and it is only now I am having difficulty in starting it. As said, I have replaced numerous parts but cannot solve this issue. I have replaced the primer bulb. After priming and attempting to start the bulb appears to be empty and does not seem to hold the fuel. Often the motor will fire but fail to run until I semi choke the unit. Sorry this is the best way I can explain the problem, thanks Bill

It sounds as if the primer may not be functioning. Can you look at where the fuel is supposed to come out, while pumping it? (It may be in the carburetor venturi, from the main jet).