Where do we go now?

[still]

I have a five year old Stihl MS-170 that has not seen alot of use for about a year. It started right up yesterday. I ran it all the way out of fuel and when I filled it up again it would not start. I replaced the plug and fuel filter. I tried putting some straight in the chamber and that did not work. I tried starting fluid and that did not work. I hate to waste the time and money on a rebuild kit for the carburetor if that is not the problem. Since it did not start or fire with fuel straight in the chamber I am thinking it is not a fuel problem. Anything else I can try before I break it down for the carburetor rebuild?

 

[Bob Hedgecutter]

Pull the muffler off and give us a nice clear photo of the front face of the piston as viewed through the exhaust port in the cylinder.

 

[still]

I hope this is good enough, if not I will try to get closer. Surfaces look smooth.

 

[Bob Hedgecutter]

Well, it is good enough to see the front of the piston is not all torn up from running on a tank of raw straight gas- so thats a good starting point!

 

[still]

I was happy my model had two simple 8mm hex nuts to take of the muffler. I am still at a loss for what to try next though. Thanks for getting back though. I am almost to the point of just taking it into the repair shop.

 

[Bob Hedgecutter]

Lots of things these can suffer from- loose floor pan of the clamshell is one- sucking air in from the bottom.
Have you tried starting it again now it is cold?
Could have been simple flooding trying to start the saw warm, maybe using choke settings and flooded the combustion chamber?
Running the tank and carb empty sometimes it can be difficult for the saw to pick up new fuel and the cold start procedure actually helps.

Basically all you need is spark, correct fuel to air ratio supplied to the combustion chamber, compression and spark timing to make a two stroke run.
I am not real familiar with your E fuels and associated problems- we do not have to deal with ethanol yet where I live, so it could be something to do with that- ethanol effecting the fuel line or carb internals, but the fact the saw ran and would not restart leads me to think more a flooding issue with a warm saw getting too much fuel and not a combustible vapour.

 

[still]

I appreciate the time you have taken for a exhaustive analysis of the situation. It is not ethanol as I use an ethanol free premix. Your insight might just keep me out of the repair shop.

 

[Bob Hedgecutter]

Sometimes the repair shop is easier and less frustrating- but then it depends on the shop and if you have to deal with a genuine old saw repairer or a pimply faced cashier that studied from youtube university.

 

[still]

Good point