Stihl MS170 running problems

[rapserv]

Bought a MS170 a few months back to carry in my caravan for cutting light firewood (max 4- 5" in diameter) and have used it about 3 times now.
The first time it ran without any issues, second time ran for about 10mins then died. Pulled it apart, cleaned everything put it back together and had trouble trying to get it started. Eventually, I gave it a quick shot of Aerostart and it fired and ran ok after that.
Used it again yesterday after it had been sitting for about a month and after cutting for about 10mins it died again!!  >:(
Tried to start it again this morning and managed to get it running but at higher revs... as soon as you reduce the revs it dies and stops .. will not idle at all. Sound like its starving for fuel. Tried new fuel and adjusted idle screw to no avail.
Have just pulled the saw apart completely for the second time today, checking everything.. including pulling the carb apart checking and cleaning all internal parts and the entire fuel line...all look ok!!
I've replaced the spark plug and air filter and readjusted the gap on the magneto as this looks to have been rubbing slightly against the flywheel (fine scratching on the flywheel... but I would not think that this could be causing the issue)
At this stage I'm really annoyed that I'm having these sorts of issues having recently just bought it.  I understand that this is not an expensive model, however I would have expected at least some reliabilty from such a brand name.
How likely is it that this could be just a fuel mix problem as many people have stated... ie must use Stihl's own oil,  I am using a 50:1 mix of Penrite "HI-PER" semi synthetic high performance, low smoke 2 stroke oil.
Any chance that it's just a dodgy carb straight out of the box??

[Caloren]

My 170 ran good for a couple of years, then got where it would die when the trigger was pulled, it would not accelerate. I could shut the saw off and restart it and it may run fine, sometimes not. Took the carb apart and found a small piece of a hard clear substance, thought it was probably some sealer used on the welch plugs. cleaned it out and ran fine for a year or so, then started the same thing again. This time I put a kit in and it did good from then on. This year it was not running as good as I would like but the Zama carb has no adjustments other than idle speed, so I bought a Walbro and replaced the Zama so I could have low and high adjustments. It runs great now. Have had this saw for 10 or 11 years now and find I use it more than any of my other saws.

[dougand3]

I'd try a new fully adjustable carb...should be $10 on aussie ebay.

[stevekw]

My 170 did the same thing a few years ago. Its about 20 years old. I just took the carb apart and cleaned everything up. Has been running fine since. It is a very finicky saw tho if it gets any dirt in the carb. As far as the fuel mix, I only run the Stihl HP Ultra synthetic. A very good saw mechanic at my local implement store told me when I recently bought a new MS311, to use this pre mix only. He said hes tore 100s of customers saws apart over the years and the amount of carbon built up inside the ones not running Stihl synthetic was quite a bit more than the ones that were. All 3 of my saws start and run pretty good running the Stihl oil.

[LeeB]

how many months is a few months? Is it still under warranty? Take it back to the dealer.

[joe_indi]

If the muffler is the type that has a screen, check it is clogged. Clogging could cause the saw to run lean.
A setting to start with is turn the single screw anticlockwise to stop and then turn 2 turns clockwise. Once the saw starts and has warmed up, turn the screw anticlockwise to decrease idle rpm and clockwise to increase it.
One way of setting the carb for a richer mid range and high is to bend the metering lever slightly upwards. This will give a higher fuel level in the chamber. But do it carefully. If it is bent too much, it could cause flooding.
To get a richer mixture at high speed, you could either use a bigger jet (difficult to lay your hands on) or remove the jet and use a pin or similar to enlarge the jet slightly. I use a go/no-go method. I get a pin that barely enters the hole, I then use a file or emery to give the tip of the pin a square profile and then rotate the pin in the jet.

[rapserv]

My 170 ran good for a couple of years, then got where it would die when the trigger was pulled, it would not accelerate. I could shut the saw off and restart it and it may run fine, sometimes not. Took the carb apart and found a small piece of a hard clear substance, thought it was probably some sealer used on the welch plugs. cleaned it out and ran fine for a year or so, then started the same thing again. This time I put a kit in and it did good from then on. This year it was not running as good as I would like but the Zama carb has no adjustments other than idle speed, so I bought a Walbro and replaced the Zama so I could have low and high adjustments. It runs great now. Have had this saw for 10 or 11 years now and find I use it more than any of my other saws.

thanks for that response.
I had read in other posts about people replacing the carb with a Walbro unit and this is certainly an option, however, you would think that as the saw is only about 3 months old and hardly been used that this should not be necessary. If I can't find a fix before too much longer, I think I'll just return the saw under our consumer protection laws  >:(

[rapserv]

My 170 did the same thing a few years ago. Its about 20 years old. I just took the carb apart and cleaned everything up. Has been running fine since. It is a very finicky saw tho if it gets any dirt in the carb. As far as the fuel mix, I only run the Stihl HP Ultra synthetic. A very good saw mechanic at my local implement store told me when I recently bought a new MS311, to use this pre mix only. He said hes tore 100s of customers saws apart over the years and the amount of carbon built up inside the ones not running Stihl synthetic was quite a bit more than the ones that were. All 3 of my saws start and run pretty good running the Stihl oil.

I've had the carb apart twice now and can't find any problems within, but I think it might be worth trying the Stihl HP Ultra as I have heard before that these types of problems can be experienced if using a different brand of oil mix. I did not use the Stihl brand of oil as it's twice the price of other quality brands and sounded like a bit of a rip off... maybe it is just the oil  >:(

[rapserv]

how many months is a few months? Is it still under warranty? Take it back to the dealer.

thanks Lee..
this may be just what I will do as its only 3 months old as of today!!
If I was able to work on it in my workshop I would probably persist, however I'm traveling around in my caravan and it is not that easy to carry out repairs whilst on the road... particularly in some of the outback areas I travel through and the saw needs to be reliable (that's why a bought Stihl) If I knew in advance that I was going to have these sorts of problems I probably would have tried to find a way to fit my larger Husky Rancher in the van instead. :-\

[rapserv]

If the muffler is the type that has a screen, check it is clogged. Clogging could cause the saw to run lean.
A setting to start with is turn the single screw anticlockwise to stop and then turn 2 turns clockwise. Once the saw starts and has warmed up, turn the screw anticlockwise to decrease idle rpm and clockwise to increase it.
One way of setting the carb for a richer mid range and high is to bend the metering lever slightly upwards. This will give a higher fuel level in the chamber. But do it carefully. If it is bent too much, it could cause flooding.
To get a richer mixture at high speed, you could either use a bigger jet (difficult to lay your hands on) or remove the jet and use a pin or similar to enlarge the jet slightly. I use a go/no-go method. I get a pin that barely enters the hole, I then use a file or emery to give the tip of the pin a square profile and then rotate the pin in the jet.

thanks joe..
checked the muffler/screen when I first started having problems as I know from previous experience that nasty little wasps like to build their nests in any little cavity they can find (so don't bend over for too long  )  and especially exhaust ports... severely limiting or blocking the port and preventing the free flow of exhaust gasses.  At this stage I don't want to modify the saw as it is still under warranty.