home Fix label Garden Tools label_important Chainsaws

Stihl MS170?

Wouldn't start.
If I prime it directly with a capful of fuel it will run until the fuel runs out!
So took the carb off and cleaned it.
Now it will start on 1/2 choke, but die after 10 secs or immediately die if i use the accelerator.
I can keep it running by flicking the switch between full and half choke.
Any ideas?

Jay, September 2010

home Fix label Garden Tools label_important Chainsawsdone

Well I had it apart, there was a bit of carbon on the pistonhead which I cleaned off, the rings were fine, the cylinder was fine.

I put it all back together and there is the same problem. I'm going to try new filters (evfen though they look clean) and then give up and take it to get repaired

Jay, September 2010

Has it actually scuffed the piston? if you have excssesive carbon on the piston it could gum the ring in and cause problems, excessive carbon is due to poor quailiy oil, too much oil, incorrect grade of oil, running rich,poor air filter maintenance,ring wear, light carbon marks should not effect the running.I still maintain what i said in my first post.

Husqvarna man, September 2010

It wasn't the carb settings.
When I take the muffler off I can see that the piston seems burnt where the exhaust leaves the cylinder.

Would a burnt piston cause the problem?

Jay, September 2010

I'll have a play around with the carb settings, although the MS170 only has 1 screw not the Hi & Lo on other Stihl models

Jay, September 2010

All the symptoms you described in your original post indicate to me the High setting on the carb is too lean.

pleasant, September 2010

i tried starting it without the muffler on and I had the same problem.
However when I took the muffler off it was soaked in fuel and when I was running it on choke excess unburnt fuel was coming out.

This makes me think its unlikely to be related to insufficient fuel.

Jay, September 2010

Running too lean, blocked fuel filter in the tank, cracked or broken fuel hose, internal carb fuel screen blocked, impulse pipe broken or disconnected, indudtion tube cracked,massive air leak ( crank seals )

Husqvarna man, September 2010