MS170 Issue

[LAtree]

No. Pull fuel line to look for some kind of hole

 

[Michael E]

Before you throw any more parts at the saw, you should properly diagnose the problem. To run, your saw needs compression, fuel, spark and impulse. Since you can start it with some fuel in the cylinder, it obviously has compression and spark. It either doesn't get any fuel from the tank to the carburetor or the carburetor can't deliver to the cylinder. This could be a problem with impulse or pump diaphragm or fuel line. The saw shows the same symptoms with two different carbs, so I would look elsewhere for now. You can't have a broken impulse line (hose), because you don't have an impulse line. Since the saw runs only with a full tank, I would properly check the fuel line. If it has a hole, the saw would suck in air instead of fuel. If you have a pressure/vac test tool, you can use that to check and search for a leak.

 

[LAtree]

Yeah that’s what I am thinking. Any idea what problem Stihl was having with the carbs on these.

 

[J D]

Biggest problem these carbs have is that they are fitted to saws that are tipically used infrequently by homeowners & they sit with old fuel in them.
Other issue is that they are non adjustable & typically jetted rather lean (older ones aren't so bad)
Dump fuel into a glass jar & inspect for contaminants.
Check/ replace fuel line & filter (they can look fine but not be)
Check choke ia working as it should.
Open carb & check fuel is getting into carb.
A serious case leak could cause lack of impulse