Stihl Ms 170 Carb

[djg james]

Check to see that the throttle rod does in fact back out when you let up on the trigger. The spring on the carb is supposed to send it backwards. Something sounds jammed up.

BTW, did you notice how "easy" Stihl made it to remove/install the carb? Those mounting bolts are almost (but not quite) inaccessible. I wonder if this saw, resting at the bottom of their product line, was originally designed to be a throwaway.

I'll check this on Friday. It was working fine before I put the air filter on. An getting the nuts on... I've dropped them inside several times. I now put the nut in a socket which goes on an extension chucked in a small impact driver (small, so I'm not worried about stripping). I hold the driver upright and tip the saw down so the nuts won't fall out before engaging.

 

[djg james]

The idle screw on this carb is simply an air bleed which is why it is a left hand thread. With it full CCW (all the way in) the saw should NOT idle but die. If it does run and/or run fast you likely have an air leak.


This sounds like an air leak. These are notorious for leaking around the pan gasket/seal.

The new carb did come with two fiber board gaskets which I did NOT use BECAUSE the saw never had any gaskets. However, as with my others saws, they were worked on by others at some time. So maybe they were never replaced at the shops.

 

[HarleyT]

I'll check this on Friday. It was working fine before I put the air filter on. An getting the nuts on... I've dropped them inside several times. I now put the nut in a socket which goes on an extension chucked in a small impact driver (small, so I'm not worried about stripping). I hold the driver upright and tip the saw down so the nuts won't fall out before engaging.

So you are having trouble gripping your nuts?

 

[HarleyT]

View attachment 825626

The new carb did come with two fiber board gaskets which I did NOT use BECAUSE the saw never had any gaskets. However, as with my others saws, they were worked on by others at some time. So maybe they were never replaced at the shops.

You don't need those,
or if you want to put one between the air filter housing and the carb, it wouldn't hurt.

 

[djg james]

I use a special tool to hold my nuts (they're kind of small).

 

[djg james]

You don't need those,
or if you want to put one between the air filter housing and the carb, it wouldn't hurt.

So maybe I'm not getting the nuts torqued down evenly using the driver and am getting the air leak between the manifold and the carb?

 

[HarleyT]

I'll have to compare it to my Brother's MS 170.

Any ideas?

If his runs fine, swap the carbs, and stop blowing money. See what happens and let us know.

 

[HarleyT]

Also, the inside lip of the intake boot, there should be a white expander ring.

 

[djg james]

If his runs fine, swap the carbs, and stop blowing money. See what happens and let us know.

OMG!! He'd kill me. He's doesn't like me tinkering around with his stuff. He just doesn't appreciate my jury rigging and problem solving skills.

 

[djg james]

I think the ring is there; I'll check on Friday.

 

[HarleyT]

It is actually "Jerry rigging" around here,

jury rigging happens a lot over in Illinois.....

 

[djg james]

Jury-rigged means something was assembled quickly with the materials on hand. Jerry-built means it was cheaply or poorly built. Jerry-rigged is a variant of jury-rigged, and it may have been influenced by jerry-built.

I guess I do a little of both.

 

[Wood Doctor]

Glad to see you guys are trying to make a comedy hour out of this repair. Maybe that's what a Stihl 170 deserves and why I said this saw might have been dubbed a throwaway by the folks in Germany when it was created -- a Wild Thing competitor.

 

[HarleyT]

Jury-rigged means something was assembled quickly with the materials on hand. Jerry-built means it was cheaply or poorly built. Jerry-rigged is a variant of jury-rigged, and it may have been influenced by jerry-built.

I guess I do a little of both.

Glad to see you guys are trying to make a comedy hour out of this repair. Maybe that's what a Stihl 170 deserves and why I said this saw might have been dubbed a throwaway by the folks in Germany when it was created -- a Wild Thing competitor.

Sounds like someone is cranky about not having good luck with this model.........

 

[djg james]

Glad to see you guys are trying to make a comedy hour out of this repair. Maybe that's what a Stihl 170 deserves and why I said this saw might have been dubbed a throwaway by the folks in Germany when it was created -- a Wild Thing competitor.

I agree, two weeks ago, the same farm store had this saw on sale for the same price I bought mine 20-25? years ago. I almost bought one (not really). I'm sure this is a simple fix, either a bad aftermarket carb or something I'm not doing right.
And far as comedy, when I was younger I enjoyed tearing into projects and staying with it until it was fixed. Now, I start and stop so many times, it comical I sure.
Frustrating.

 

[djg james]

Sounds like someone is cranky about not having good luck with this model.........

As I've said before, I love this saw. I have tackled 24" logs when my 038 was in a 'reputable' shop for 6-8 months. Used it hard and the only thing that went out is the oiler. Which is the next thing I have to fix.

 

[Wood Doctor]

Harley, I fixed this model. It was not easy. I'm not cranky at you or anyone else. I appreciate good humor and sometimes that's what it takes to fix anything. Keep up the good work.

 

[djg james]

If I haven't said it before, I want to thank the both of you, as well as others, for your help. I don't like the 'like' button; there should be a 'Thank You' button.
I've been through several repair shops with bad results. That's why I've been trying to fix and service my saws myself now. I'm sure it shows I don't have a lot of experience and I appreciate you guys walking me through it.

 

[SteveSr]

You don't need those,
or if you want to put one between the air filter housing and the carb, it wouldn't hurt.

Just make sure that you use the one with the impulse hole in the right place! Nothing like Chi-com junk!

 

[Vintage Engine Repairs]

No I haven't; I don't have that capability.
To recap, the saw was running fine several years ago. I let it set and then recently tried to use it. It would run fine with the trigger locked on, but then would die when released or you would constantly have to pump the throttle to keep it going. New fuel filter and line. Everyone here suggested it was carb issues, so I took it apart and soaked it several times. Still the same thing.
Then they suggested time for a new carb. And now we're up to the point of the new carb not working.

All good a video would really help if you can? Is the new carb OEM and designed for this specific model saw? I’d guess two things, either it’s got an air leak or the metering diaphragm in your old carb needs replacing. In fact see if the new diaphragm and gaskets will fit the old carb. Swap it over and put old one back in. See how it runs. If it’s still got issues, I’d say (and I think it’s the most likely cause) it has an air leak. You can buy a cheap tester for 30 USD on eBay, it has a multitude of uses