New Stihl MS 170 stopped running, now hard to start & won't stay running

[user 122190]

Mechanics can be like members of this forum. Seen it, solved it, know about it. Everything else is just a WAG, i.e. heard about it or it sounds familiar, really haven't any clue, but this IS what the problem is and the solution, and if not then you didn't describe the problem correctly.

We've been out of town but stopped by another Stihl dealer nearby (didn't have the chainsaw with us) to see about getting a new spark plug just to rule that out before taking it in to our local dealer on Monday. Described the symptoms and showed him a picture of the plug and he told us to just make sure the plug is clean and implied the problem was likely the gap size in the spark plug, and that the saw was running rich. Sold us a gap tool to check it but I really doubt when I end up measuring it's going to be out of spec.

I do have serious doubts some of the things he was saying though, he also told us

1. It's unsafe to dump old 50:1 gas+oil mix into the car to get rid of it because it could cause damage, as not only did our local dealer specifically recommend that to get rid of it, but I've read at least a dozen threads/articles saying it's perfectly fine to get rid of it this way since cars burn oil all the time and if it's mixed in with a full tank it would probably be like an 800:1 ratio

and

2. He also said we shouldn't have used REC-90 ethanol free fuel and should have used "premium fuel" (i.e. 91/93 octane from the pump) instead as that's what Stihl uses and that Premium fuel contains no ethanol. I know for a fact this isn't true and any regular gas you get at the pump regardless of octane will contain ethanol likely in the 10% range. He also used this opportunity to recommend buying the $30 Stihl Motomix which I declined. And his reasoning as to why it didn't get through the original tank of gas was that the local dealer put bad gas in it (so both of our mixes must have been bad).

 

[wzd218]

Plug gaps probably not your issue.

1. If its not good enough for a chainsaw, why run it through your car? Dispose of it another way.
2. Sales pitch/dude doesnt know what hes talking about. Wouldnt of taken half a liter of fuel to all the sudden act up.

Didn't mean just about the gas we have left over, but he was saying you never get rid of ANY mixed gas that way. I'm probably going to have to burn it or something, I've called around and nothing around here will take gas/gas mix, not even at the waste recycling place where you can pay to get rid of used motor oil.

And he did actually say he was a mechanic/marine mechanic, but honestly when he was talking about there being no ethanol in premium gas I really find that hard to believe, not to mention specifically cautioning against the (100% gas) ethanol free fuels (which I planned on getting based on my research even before my local dealer recommended it when I bought the saw). Honestly sounded like he didn't know what I was talking about when I said ethanol free gas and was just trying to sell the motomix.

 

[user 122190]

In my area, a few gas stations sell ethanol free gas (premium), others don't. And some only sell it certain times of the year. He might have been trying to generalize. Often times getting to specific, and people get offended. Like you are or bragging, or talking down to them, or just trying to put them to sleep or something.

 

[SteveSr]

Didn't mean just about the gas we have left over, but he was saying you never get rid of ANY mixed gas that way. I'm probably going to have to burn it or something, I've called around and nothing around here will take gas/gas mix, not even at the waste recycling place where you can pay to get rid of used motor oil.

And he did actually say he was a mechanic/marine mechanic, but honestly when he was talking about there being no ethanol in premium gas I really find that hard to believe, not to mention specifically cautioning against the (100% gas) ethanol free fuels (which I planned on getting based on my research even before my local dealer recommended it when I bought the saw). Honestly sounded like he didn't know what I was talking about when I said ethanol free gas and was just trying to sell the motomix.

100% WRONG on BOTH counts. Looks like you found a dealer to AVOID! Old mix you can run in your car or lawnmower. Ethanol is not only an oxygenate but MAINLY an octane booster when added to gas. This means that 90 octane pump gas would only be about 87 without the ethanol therefore the refineries don't have to do as good a job refining it. Thanks to the ethanol mandate just about all gas (at least in my state) has 10% ethanol in it.

 

[wzd218]

Tested the spark plug gap just to make sure since the guy at the other shop sold it to us, but it was the right size - at least, close enough to the right size, since the tool he sold us starts at .025" and goes up in sizes, and the proper gap according to the manual is .02" (none of them can fit in the gap). Even told us at the store it should be at 30 thousandths of an inch which isn't the spec. I also tested running it 1 more time after the last time I cleaned the plug, and it ran for about 3 minutes and stopped, the plug was black powder again right after that.

But - I just got back from my local dealer and he immediately put his finger in the gas tank and he said it felt off, like there was too much oil in it, even asked if I accidentally mixed bar oil in or something. He swapped out the gas and tested it for a couple minutes and it ran good, but I'll have to wait and see after a while to see if it's fixed or not by going through that newly filled tank.

So I guess it's looking like I might be an idiot and it's a fuel issue like it probably is 95% of the time. Don't know what I did wrong in the mix, it was a new gas can, poured 1 gallon in (paid for 1 gallon on the pump, and it went up to the 1 gallon line on the can) then poured the whole 2.6oz oil can in, then shook it. I don't see any obvious visible gunk or anything like oil stuck on the plastic filter thing inside the can. Also still not sure why it stalled out after the first 30 minutes on the original tank then (maybe idling fouled the spark plug enough that it stalled a couple minutes later and the apparently bad gas didn't help anything?).

I checked the spark plug after bringing it home and it looks a lot cleaner, when I brought it in it was all black carbon. I'm not sure if he quickly cleaned it in the back of the shop or if it just got clean by running it. But unless it starts having problems again when I go through the new gas, that was probably the issue.

Edit: Also asked about the white smoke I was seeing both when running it originally and after it started having issues and he said it's normal to see a small amount of white smoke coming out like that.

 

[SEAM]

I have at least 3 or 4 people come in with a "don't run" situation where bar oil was filled in the fuel tank by accident - and yes, with bar oil in the fuel there will be a lot of white smoke. So, bar oil is a possibility, but it usually happens to people using two or more saws with reversed oil/fuel fillers (on some tophandles the bar oil filler is at the rear and the fuel filler at the front of the saw or both fillers one above the other, so easily confused when using both at the same time).

 

[wzd218]

Well I've had some time to get it running and cut some stuff and it's having the same problems as before, so it looks like it might not have been the fuel after all (or at least it wasn't what's been causing the stalling), haven't even opened the tank after it was swapped.

Starts, runs decent and can cut for a few minutes with occasional problems revving up, then shut off. I waited a few minutes and did a warm start (no choke, started on normal idle) to try again and the same thing, runs for a few minutes and shuts off. No discernible difference in the spark plug appearance after it shut off. Didn't notice much if any smoke so I guess it's still possible the gas before might have had too much oil, even though it was 2.6oz to 1 gallon, maybe it didn't mix right or something (I'm not a gas expert so I have no reason to not believe what they said about the oil when he put his finger in the tank) but it looks like I'll have to take it back again.

Also, is it normal for a chainsaw to have a hard time spinning the chain when you first start on a warm start? After I started it that way, I pulled the throttle and it wasn't spinning, I had to triple check to make sure the chain break was off, but it started going after I waited about 15 seconds.

 

[user 122190]

Well I've had some time to get it running and cut some stuff and it's having the same problems as before, so it looks like it might not have been the fuel after all (or at least it wasn't what's been causing the stalling), haven't even opened the tank after it was swapped.

Starts, runs decent and can cut for a few minutes with occasional problems revving up, then shut off. I waited a few minutes and did a warm start (no choke, started on normal idle) to try again and the same thing, runs for a few minutes and shuts off. No discernible difference in the spark plug appearance after it shut off. Didn't notice much if any smoke so I guess it's still possible the gas before might have had too much oil, even though it was 2.6oz to 1 gallon, maybe it didn't mix right or something (I'm not a gas expert so I have no reason to not believe what they said about the oil when he put his finger in the tank) but it looks like I'll have to take it back again.

Also, is it normal for a chainsaw to have a hard time spinning the chain when you first start on a warm start? After I started it that way, I pulled the throttle and it wasn't spinning, I had to triple check to make sure the chain break was off, but it started going after I waited about 15 seconds.

Take the SAW to the DEALER.

 

[SteveSr]

Well I've had some time to get it running and cut some stuff and it's having the same problems as before, so it looks like it might not have been the fuel after all (or at least it wasn't what's been causing the stalling), haven't even opened the tank after it was swapped.

Starts, runs decent and can cut for a few minutes with occasional problems revving up, then shut off. I waited a few minutes and did a warm start (no choke, started on normal idle) to try again and the same thing, runs for a few minutes and shuts off. No discernible difference in the spark plug appearance after it shut off. Didn't notice much if any smoke so I guess it's still possible the gas before might have had too much oil, even though it was 2.6oz to 1 gallon, maybe it didn't mix right or something (I'm not a gas expert so I have no reason to not believe what they said about the oil when he put his finger in the tank) but it looks like I'll have to take it back again.

Also, is it normal for a chainsaw to have a hard time spinning the chain when you first start on a warm start? After I started it that way, I pulled the throttle and it wasn't spinning, I had to triple check to make sure the chain break was off, but it started going after I waited about 15 seconds.

Does the saw shut off while idling or while cutting or does it just stall when returning to idle? If it is while idling there is an adjustment that will raise the idle speed to keep this from happening.

If the engine is cold it may not want to rev up. This should go away once the engine is fully warmed up.

Got anyone who can take and post a video of the saw misbehaving? Sure save a LOT of guessing!

 

[farmer steve]

We've been out of town but stopped by another Stihl dealer nearby (didn't have the chainsaw with us) to see about getting a new spark plug just to rule that out before taking it in to our local dealer on Monday. Described the symptoms and showed him a picture of the plug and he told us to just make sure the plug is clean and implied the problem was likely the gap size in the spark plug, and that the saw was running rich. Sold us a gap tool to check it but I really doubt when I end up measuring it's going to be out of spec.

I do have serious doubts some of the things he was saying though, he also told us

1. It's unsafe to dump old 50:1 gas+oil mix into the car to get rid of it because it could cause damage, as not only did our local dealer specifically recommend that to get rid of it, but I've read at least a dozen threads/articles saying it's perfectly fine to get rid of it this way since cars burn oil all the time and if it's mixed in with a full tank it would probably be like an 800:1 ratio

and

2. He also said we shouldn't have used REC-90 ethanol free fuel and should have used "premium fuel" (i.e. 91/93 octane from the pump) instead as that's what Stihl uses and that Premium fuel contains no ethanol. I know for a fact this isn't true and any regular gas you get at the pump regardless of octane will contain ethanol likely in the 10% range. He also used this opportunity to recommend buying the $30 Stihl Motomix which I declined. And his reasoning as to why it didn't get through the original tank of gas was that the local dealer put bad gas in it (so both of our mixes must have been bad).

Unless you have 10 gallons dump your old gas in your car or lawnmower. Back in my poor days I pinched pennies and ran 87 octane in my saws. Never blew any up. Take the saw back to where you bought it!

 

[wzd218]

Take the SAW to the DEALER.

Going back again once they open after the weekend since their fuel didn't fix it.

Does the saw shut off while idling or while cutting or does it just stall when returning to idle? If it is while idling there is an adjustment that will raise the idle speed to keep this from happening.

If the engine is cold it may not want to rev up. This should go away once the engine is fully warmed up.

Happens when it's idling, don't think I've had it happen while actually cutting or pulling the throttle. Does seem to have trouble -sometimes- when pulling the throttle, but in terms of the stalling and turning off it's been when I'm not making a cut or am walking over to do one. Could a bad idle setting on the carb cause both the stalling after idling and occasional trouble revving up? I'll look at adjusting that based on the manual, where it says to set it to where the chain starts to rotate and then backing off 1/2 a turn

Edit: If I turn the idle screw like it says counterclockwise until it's seated, then 2 turns clockwise (should be the factory setting) it won't run for more than a few seconds now, starts and stalls out almost immediately

 

[SteveSr]

Happens when it's idling, don't think I've had it happen while actually cutting or pulling the throttle. Does seem to have trouble -sometimes- when pulling the throttle, but in terms of the stalling and turning off it's been when I'm not making a cut or am walking over to do one. Could a bad idle setting on the carb cause both the stalling after idling and occasional trouble revving up?

Possibly, if it is idling too slow it may not want to rev up especially if it is cold outside and if the engine isn't fully warmed up.

Edit: If I turn the idle screw like it says counterclockwise until it's seated, then 2 turns clockwise (should be the factory setting) it won't run for more than a few seconds now, starts and stalls out almost immediately

What is your elevation and ambient temperature? Factory carb settings are for sea level (Virginia Beach) and temperatures of 70F.

Will the idle screw increase the idle to the point that the chain starts to run with the chain brake off?

 

[SEAM]

If I turn the idle screw like it says counterclockwise until it's seated, then 2 turns clockwise (should be the factory setting) it won't run for more than a few seconds now, starts and stalls out almost immediately

2 turns out is the factory setting that allows the engine to run - the proper idle speed should be set after that with the engine warmed up. You may have to adjust the screw in + direction for a slightly higher and more stable idle speed. The "how to" is detailed in the owner's manual.

 

[husqORbust]

Turn the idle screw in clockwise all the way. Does the saw run with a screaming idle/chain and freely rev up to cutting speed and then return back to its screaming idle when letting off the throttle? If so back the screw off until the chain JUST stops spinning. That is the proper idle speed setting if you dont have a tach. Now with the idle properly set, does it run mint and not stall out and not have hard starts and...etc.

If not then then the idle screw is not your issue.

The saw will likely run ANYWHERE between 32:1 and straight gas. Now, obviously, 50:1 is the max you want to run, but the point is it will STILL run. You would have to try REALLY hard to screw the ratio up so bad it wont run. In any event, it'll either run till seizure, or run till the plug fouls. It wont run intermittantly because of a bad ratio.

It will also run MINT with 6 month old mix taken straight from a can that was tightly sealed.

For it to be a fuel quality/ratio issue, the fuel would have be really, REALLY bad.

Fuels not the issue. And gonna go ahead and say idle speed wasnt the issue either.(although it might be another issue on top of the first one if its adjusted based on a **** running saw)

Bottom line take it back to the dealer and tell them it still runs like crap with the fuel THEY supplied.

 

[user 122190]

So, what is the status on this saw?