MS 170 - Gas Fumes??

Bigfoot870 · May 06, 2016, 11:59:37 AM

Hey guys!! I'm new here, but have been in the woods of Nova Scotia, running saws, since 1983. I have always run pro saws, but due to a bad back, I purchased the little Stihl, April 2014. I used it for about four hours, that spring, then, for (other) health reasons, I didn't use until two weeks ago. The little bugger works great, even with the OEM non-adjustable carb, but it seems to give off excessive gas fumes when I'm limbing (I.e. spruce). I can't find any gas leaks. Any ideas? Thanks

DelawhereJoe · May 06, 2016, 12:42:05 PM

My first guess would be the fuel cap, I've had a few on string trimmers go bad and is the first thing you smell after you run it.

joe_indi · May 06, 2016, 01:19:04 PM

The vent for both the oil and fuel tanks of the 170 (and the 180) are not in the caps. They are tiny one way valves that open to let air into the tank(s). They are fitted on the tanks and are visible if the starter cover is removed. If, by chance, the one on the fuel tank has come slightly off the seat chances are you will get some fumes, but given the close proximity of the flywheel with its fins, such fume would be blown away. So I would rather look at the fuel hose at the point where it connects to the carb, or a slightly loose cover on the pump side of the carb, that is if you can be sure the engine is not flooding each time you shut it off, in which case it could be a leaking metering valve.

DelawhereJoe · May 06, 2016, 06:12:36 PM

I was just saying to check the rubber o-ring or rubber washer that seals the cap on. I see it constantly from pool that sit over winter that the o-rings dry and crack or flatten on one side and leak water. If its sat for 2 years theres a good chance the ring dried out. But your answer will more then likely be the correct one....I'm just a poolguy that cuts firewood.

Bigfoot870 · May 08, 2016, 07:45:05 AM

Thanks guys, but it's not the gas cap and she's not flooding, when shut off.

However, when cold, she takes six or seven pulls, to get that first kick, then two more to actually start. Is this normal?

OldJack · May 08, 2016, 02:37:47 PM

My 170 takes about that many pulls on a cold start.

Bigfoot870 · May 08, 2016, 05:37:42 PM

Quote from: OldJack on May 08, 2016, 02:37:47 PM
My 170 takes about that many pulls on a cold start.

Thanks Jack!!

Bigfoot870 · May 12, 2016, 12:55:01 PM

Apparently, the little bugger is still breaking in, even though it has about ten tanks of gas through it. While cutting maple firewood, at my camp, on Tuesday, it wouldn't start, after me taking a two minute break, unless I put it on fast idle. Once it started, it idled without stalling and worked fine. The third time it wouldn't start (yes, I take a lot of short breaks, due to a bad back), I decided to simply try engaging the throttle twice, before starting, and that worked fine. I took it to the dealer, yesterday, and the tech said it was idling at 2400 rpm, and he upped it to 2800 rpm (per spec). I had already increased the idle speed myself, awhile back. I hope it's nothing more than the idle setting, as my warranty is up on May 22nd, and I'm not sure how much I'll get out before then.

Bigfoot870 · May 18, 2016, 09:47:18 AM

Quote from: joe_indi on May 06, 2016, 01:19:04 PM
The vent for both the oil and fuel tanks of the 170 (and the 180) are not in the caps. They are tiny one way valves that open to let air into the tank(s). They are fitted on the tanks and are visible if the starter cover is removed. If, by chance, the one on the fuel tank has come slightly off the seat chances are you will get some fumes, but given the close proximity of the flywheel with its fins, such fume would be blown away. So I would rather look at the fuel hose at the point where it connects to the carb, or a slightly loose cover on the pump side of the carb, that is if you can be sure the engine is not flooding each time you shut it off, in which case it could be a leaking metering valve.

I think you were bang on Joe, as I ran it for a half tank on Saturday, and when I took it off my truck, an hour later, the gas was running out at the bottom of the start cover. It's still under warranty, so the shop is looking at today.

Bigfoot870 · May 18, 2016, 10:27:32 AM

The shop tech just called and said the gas leak was caused by a piece of dirt in the gas tank vent. This is my first non-professional saw. Is this sort of issue normal?

joe_indi · May 18, 2016, 11:11:26 AM

Quote from: Bigfoot870 on May 18, 2016, 10:27:32 AM
The shop tech just called and said the gas leak was caused by a piece of dirt in the gas tank vent. This is my first non-professional saw. Is this sort of issue normal?

The vent opens to let in air into the tank when there is a partial vacuum in the tank, the tiny valve snaps open for a couple of milli seconds and yes, the velocity of air flowing in could suck a very tiny bit of something, a bit of saw dust, or a bit of fluff from the starter rope, just enough to prevent the valve from closing fully.Enough to cause a leak. This is extremely rare, but I think your saw is an exception. ;D

Bigfoot870 · May 18, 2016, 03:43:47 PM

Quote from: joe_indi on May 18, 2016, 11:11:26 AM
Quote from: Bigfoot870 on May 18, 2016, 10:27:32 AM
The shop tech just called and said the gas leak was caused by a piece of dirt in the gas tank vent. This is my first non-professional saw. Is this sort of issue normal?
The vent opens to let in air into the tank when there is a partial vacuum in the tank, the tiny valve snaps open for a couple of milli seconds and yes, the velocity of air flowing in could suck a very tiny bit of something, a bit of saw dust, or a bit of fluff from the starter rope, just enough to prevent the valve from closing fully.Enough to cause a leak. This is extremely rare, but I think your saw is an exception. ;D

Thanks Joe!! I hope it's a rare occurrence, however, I'm confident that I can do my own "fix" when the warranty ends.

joe_indi · May 19, 2016, 01:57:14 AM

Quote from: Bigfoot870 on May 18, 2016, 03:43:47 PM
..........I'm confident that I can do my own "fix" when the warranty ends.

You will need a syringe filled with fuel for that.
Remove both filler caps and undo the 4 screws of the starter cover and lift it out of the way. The tank vent is now accessible. Use the syringe with fuel to blow fuel through the vent into the tank.
That is all.
In case you want to do the same for the oil tank vent, use a bit of diesel.
Joe

Bigfoot870 · May 25, 2016, 08:21:09 AM

Quote from: joe_indi on May 19, 2016, 01:57:14 AM
Quote from: Bigfoot870 on May 18, 2016, 03:43:47 PM
..........I'm confident that I can do my own "fix" when the warranty ends.
You will need a syringe filled with fuel for that.
Remove both filler caps and undo the 4 screws of the starter cover and lift it out of the way. The tank vent is now accessible. Use the syringe with fuel to blow fuel through the vent into the tank.
That is all.
In case you want to do the same for the oil tank vent, use a bit of diesel.
Joe

Thanks Joe

Bigfoot870 · June 01, 2016, 09:27:43 AM

Less than two tanks later and it's back in the shop. The tech said that he actually replaced the tank vent check valve, the last time. I can only guess that it's something else.......

Left Coast Chris · June 01, 2016, 09:49:41 AM

Hope they figure it out for you. My MS 170 is maybe 6 or 7 years old and has always worked fine. It has not sat for over a year though. I do use only premium non lead fuel from name brand stations. The California gas is oxygenated also but I try to avoid stations I know have higher ethanol.

Bigfoot870 · June 05, 2016, 12:03:15 PM

Chris, The tech had the carb and tank under pressure (separately or at the same time, I don't know), as advised by Stihl, but no leak was found. He's a bit of a jerk (he's the mechanic for what is actually an equipment rental shop, which also deals in Stihl products), and I don't have the patience to deal with him anymore, so I gave up and didn't ask if he actually ran the saw. Whereas, the tank vent check valve has already been replaced, I plan to check the gas line, itself, for a leak and install a new carb kit (thanks to donyboy73 on YouTube). I'm still puzzled as to how the saw can work just fine, yet still leak gas.

Joe, since watching donyboy's videos, I now know what you mean by a metering valve........which I know as a diaphragm

When I took the carb off, to get the model number, to ensure I order the correct kit. After reassembly, I ran the saw, and still have the gas leak, which appears gas line related. It seems to be where the line fits through the tank wall?!?! :(

My Carb is a ZAMA C1Q S264. I can't find a carb kit online. Can anyone help me track one down that ships to Canada? Thanks guys

dougand3 · June 06, 2016, 09:24:31 AM

My Zama chart is from 2010 and doesn't show S264. S57 carb has been used on MS170 MS180. That kit is RB-77. It may work. A kit costs $6-$8. A new AM carb costs $9-$10.
Fuel line kits costs $6-$8. I'd try replacing them.

Bigfoot870 · June 06, 2016, 10:01:44 AM

I found the same info Doug. I'm going to get the carb rebuild kit and fuel line, through a local shop, then do the work myself

Bigfoot870 · June 06, 2016, 04:23:37 PM

After further consideration, I called the Stihl tech, to advise that the gas leak still existed. I asked if he would consider replacing the gas line, under warranty, and he agreed. Awhile later, he called back to advise that he spoke to Stihl and they authorized him to replace the fuel tank under warranty. Looks like I was wrong about him

The Stihl parts lady had to make a phone call, as her parts listings didn't call out a carb kit for the S264. Turns out that it also takes RB-77.

Bigfoot870 · July 06, 2016, 02:44:30 PM

Leak is fixed. That's the first time the tech said he ever saw a leak, where the hose goes into the tank.

sablatnic · July 07, 2016, 01:05:29 PM

I haven't seen a leak on the 170 - yet, but I've seen it on other machinery, Stihl and others, mostly brush cutters and trimmers.
The fuel line seems to shrink and become lose in the hole.
Could be the fuel causing it.

nuke1 · July 07, 2016, 07:17:33 PM

i'm glad to see you got your 170 straightened out this is the first year I've owned a 170 and I was very disturbed to find out that it was running over 15,000 out of the box during break in but lifting up the fulcrum on the main metering diaphragm fix that problem right away and I've had a couple more come in for repair since then where i found even the new zama carburetors you get from stihl for $35 apparently need to be touched a little just so you can get them to slow down to 13,000 .