MS170 wont run (1 Viewer)

[TonyC72]

I have an eleven year old MS170, which has been a great saw until recently. Upon starting from cold it ran but seemed to loose power when cutting. Since then all I have done to fix it, has not helped, and now doesn't want to start at all.

I have installed new spark plug, new gas line and filter, new carb kit (all but remove and replace welch plugs. Wasn't sure how to seal them back in). Cleaned muffler and spark arrester screen, Removed flywheel, and ensured that keyway was still intact. (spark will jump 3/16" gap on old plug). checked the duckbill thingy in the gas tank. Put fresh hi-test gas and Stihl oil in tank. I even bought a new carb online (from China of course) and it did the same thing.

It has good compression, although I don't have a gauge, but feels the same when pulling it over. Any help would be appreciated.

TonyC

 

[micruz60]

You've done all the things I would do.... Getting spark, check. Getting fuel into combustion chamber? Try cycling with the plug out, sloowwly as the chamber could be flooded? Shot 'o starting juice?
Paging D'animal... Saw guru?
I had a saw do what you've described (losing power when cutting) and wanted to rebuild with a new compression ring on piston, but then I got a newer saw for cheap, and the old one sits in a box, disassembled.

 

[TonyC72]

You've done all the things I would do.... Getting spark, check. Getting fuel into combustion chamber? Try cycling with the plug out, sloowwly as the chamber could be flooded? Shot 'o starting juice?
Paging D'animal... Saw guru?
I had a saw do what you've described (losing power when cutting) and wanted to rebuild with a new compression ring on piston, but then I got a newer saw for cheap, and the old one sits in a box, disassembled.

 

[TonyC72]

I think I did something wrong in trying to reply to Micruz60. Sorry about that.

I've had flooding when trying to start choked, and have blown out spark plug hole and dried plug, but still not starting. A couple of times it has started, but wouldn't keep running when I gave it full throttle.

Thanks for the reply Micruz60.

Tony C

 

[GLTHFJ60]

Have you checked to make sure that the air filter isn't seriously clogged?

I'd try changing the fuel filter, air filter and spark plug with some fresh gas, then if that doesn't help, you're into pulling the carb off to find the piece of debris that's causing it to stall.

 

[D'Animal]

When you removed the muffler, how did the piston look?

 

[TonyC72]

When you removed the muffler, how did the piston look?

Hi D'Animal, I took another look and the piston is shiny, and there is no scoring. The rings are also shiny, and when I pushed gently on them, I could feel movement, so would think they are not stuck in the grooves. I feel that it still is gas related as the transition from run to not run, was overnight, and it seems funny that it would be at full power, and then the next day barely able to run at all.

Thanks for your help
Tonyc

 

[splitshot]

I would suspect the online carb, a local Shihl dealer should be able to diagnose and give you an estimate.

 

[D'Animal]

Does it lose power when it warms up or when it's in the cut?
By loosing power, does it bog down and then come right back up to speed as soon as you take it out of the cut?

 

[TonyC72]

Does it lose power when it warms up or when it's in the cut?
By loosing power, does it bog down and then come right back up to speed as soon as you take it out of the cut?

It will run, but seems to be very fast idle and seems a weak mixture (no 4 cycling) and the speed control screw does very little to slow it down. It will not run up to full speed at full throttle, but just dies and stops immediately. Doesn't seem to care whether it's warm or from cold. I am in the process of testing for a crankcase leak, as would that cause these symptoms? Also, can you point me to a link on this site that would help me in a repair and rebuild if I have to go that way.

Thanks . TonyC

 

[TonyC72]

Finally did the leak test, and it seems to be OK. So, decided to put all the bits together while I still remembered where they all went, along with the rebuilt original carb. After a few pulls, it started and would rev up, and after warming up tried to cut a few 4 to5 " logs on a rack, and it ran like always. After about 10 minutes, I stopped it, and then tried to start as usual, but it wouldn't start. Tried choking it but no go. Took out the plug to see I I had flooded it, but I had not, so then saw what kind of spark I had, and it seemed much weaker than usual. Also only occasionally would it jump my test plug with 3/16" gap. I shall see if all the connections to the coil are good and clean, and proceed from there. I shall not be going any further right now, as I have a Stihl 034AV which works great and will do any further cutting with that for now. I will try to get to the bottom of this, and will let you know my findings

Thank you all for your support and advice. TonyC

 

[FJ Garrett]

Finally did the leak test, and it seems to be OK. So, decided to put all the bits together while I still remembered where they all went, along with the rebuilt original carb. After a few pulls, it started and would rev up, and after warming up tried to cut a few 4 to5 " logs on a rack, and it ran like always. After about 10 minutes, I stopped it, and then tried to start as usual, but it wouldn't start. Tried choking it but no go. Took out the plug to see I I had flooded it, but I had not, so then saw what kind of spark I had, and it seemed much weaker than usual. Also only occasionally would it jump my test plug with 3/16" gap. I shall see if all the connections to the coil are good and clean, and proceed from there. I shall not be going any further right now, as I have a Stihl 034AV which works great and will do any further cutting with that for now. I will try to get to the bottom of this, and will let you know my findings

Thank you all for your support and advice. TonyC

Tony, did you ever figure out what the problem was? I have the same saw, same problem it sounds like.
I Left the gas in last year, thought it trashed the carb , replaced it, Filter, Hoses, etc. just the same as you did, same thing,,, it wants to idle sort of, good spark when it's cold, none when warm or hot.
I am thinking it is the ignition Module... Just wondering if you figured it out on your end, thanks in advance.... Garrett