stihl not running right

[sawster]

Hi everyone I am new to the forum and hope to learn a lot. I have a stihl ms 170. about 5 years old but only used 3 or 4 times cranks right up idles great excepts fuel to a point then bogs I have checked the exhaust screen it is clean, looks brand new. I found today that if I pull the cover crank it up, restrict the hole that is in the center of the filter she will rev perfectly as soon as I move my thumb away it will not perform correctly. I am thinking fuel filter and or fuel line, because it has to have help creating the vaccum to pull the fuel. Has anyone got any suggestions thanks in advance

 

[Chainsaw Jim]

The carb likely needs rebuilt with a new kit. Usually ethanol in the fuel causes this.

 

[sawster]

thinking that the diaphram is not pulling the fuel correctly

 

[HarleyT]

Look closely at the fuel line, they are known to crack, if so, replace and rebuild carb, as dirt is likely in there too.

 

[Odin]

Sawster, HarleyT is right on the money, methinks.

My MS170 has developed the same problem. Hit the throttle and it just starts to climb, then bogs. I have to baby the throttle to get it to cut. Typically happens when it's warmed up. The rebuild kit is a nice, cheap option, but I'm thinking I'll just go whole-hog and get a fully adjustable Walbro WT-215 (for 20-ish bucks more than the rebuild kit).

My 170 is a mashup of two saws with questionable histories. Figured it would be a nice cheap educational experience trying to build one working saw. Might as well jump into adjustable carbs while the class is still in session. Heck, might even spring for a bit of a muffler mod for some extra credit...

Hope you get that little guy fixed!

 

[sawster]

I appreciate all the help. I am wondering why putting a minor restriction over the center hole allows it to run perfectly as if there is no trash or fuel starvation problem. when I slightly cover that whole it act as it should. I plan on carb rebuild and line and filter replacement. I am tempted to put a cotton ball in the hole and see what it does.

 

[HarleyT]

Covering the hole is the same as "choking" the carb, which cuts off the air, richening the mixture, which compensates for the lack of fuel. On most saws, one could possibly turn the carb mixture screws out to compensate [which is not a good idea].

But the MS170 doesn't have mixture screws..........

 

[Artemis]

If it is a fuel restriction problem, and had sat for quite some time, your fuel lines may look fine but could be collapsing when they are under a higher vacuum. A friend of mine had a stihl 011av that had collapsing lines, and he had the same symptoms. I agree with the others who have mentioned ethanol as a likely cause for carb issues.

 

[rd35]

I'm with Odin. Get yourself an adjustable carb that can be cleaned with needed!

 

[Rockjock]

I'm with Odin. Get yourself an adjustable carb that can be cleaned with needed!

WT-215 is a great option but it is not bolt on. Many threads on that subject. Fuel line carb rebuild and you have a saw that runs great. I sells dozens of them and as long as you use non e fuel, drain and run dry at the end of the season or use motomix you will have no problems.

 

[sawster]

put new zama carb on it and it sthl acts weird/. tilt the saw at a slight angle to the right and it runs good set it back up straight and it dies out.

 

[HarleyT]

What about the fuel line?

 

[HarleyT]

I am tempted to put a cotton ball in the hole and see what it does.

I apply this advice to most situations in life ......

 

[sawster]

What about the fuel line?

just ordered fuel line, seems weird that it will run tilted sideways, well hell I am a little tilted too so who knows. fuel line should be here before Friday.

 

[Stihlbillie]

Crank seals

 

[Bwildered]

My 044 got to the stage where it would only idle clutch side down! I pulled the tank filter out, pulled it apart & cleaned it thoroughly with degreaser and no more problems.
Fanks

 

[sawster]

fuel line fixed it

 

[HarleyT]

Glad you fixed her!

 

[sawster]

HarleyT you nailed it fuel line was the issue thanks for the help.