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

 

[LAtree]

Can you explain case leak

 

[Dacha]

I am not sure, but think there is no impulse line on this carb. And consequently this setup has something that mimics it, for fuel supply timing. Not sure though.

 

[LAtree]

Also should I pull jet and replace with a larger one. Or try drilling the original one. I not ready to give up on this saw yet. Stihl should make basic homeowners saw great so when people buy second and third they have had a good experience vs horrible. My first saw was an 026. Still have it and runs great. Original carb.

 

[muddy42]

put all the original parts back and return the saw to the seller for a replacement

 

[MEKinOL]

I did notice it ran for about a minute with fuel tank completely full. Then when fuel level dropped it cut off. I might try pulling fuel line out.

Purge and fuel pickup lines swapped?

 

[LAtree]

Only one fuel line

 

[Dacha]

Can chainsaw start again if you put fuel in cylinder ?

Can you repeat that a few timea to see if same thing happens every time ?

Replacement carb you used was it oem ?

 

[LAtree]

It was OEM carb. That’s why I am curious the problems a few people said Stihl had carb problems. I can try starting a few times with fuel in cylinder manually.

 

[SteveSr]

It was OEM carb. That’s why I am curious the problems a few people said Stihl had carb problems. I can try starting a few times with fuel in cylinder manually.

Was it the correct OEM carb? I think that there were a couple of versions of the MS170 and the carbs might be different. Check that the impulse passage in the manifold lines up with the hole in rear face of the carb.

 

[LAtree]

That’s a little above my level. I can get carb off. An apart. But can you send pic of which hole I am trying to line up. I just can’t id what is what on carb

 

[JimR]

Is your fuel line torn somewhere? Is your fuel filter plugged?

My thoughts too.

 

[SteveSr]

That’s a little above my level. I can get carb off. An apart. But can you send pic of which hole I am trying to line up. I just can’t id what is what on carb

This should be obvious looking at the carb face and the intake manifold. All holes have to line up. Post photos of the carb face and intake boot with the carb removed.

There is too much missing information. What is the history of this saw? When did it last run? How old is it (post a photo of the silver engine family sticker on the handle)?

Dump the fuel tank into a glass jar and look for water and other contamination. Other than that it is either fuel filter, fuel line, or impulse.

 

[rabbitpatch3]

You might try removing the fuel tank vent hose temporarily, and see if that helps. I've had to modify a couple of them on MS250's because they were too restrictive and caused the saws to starve for fuel.

 

[LAtree]

My understanding is no impulse line. So I have no idea how it is designed

 

[Dacha]

You need some luck with two stroke engines.

I could go cordless next. Less to do with luck. Just multiple batteries.

 

[LAtree]

I see inside tank a little part looks like a vent. It does look kind of closed up. Is that the vent. I assume not one in cap