MS170 Won't Run Full Throttle

[graycenphil]

My MS 170 is about two years old. Has always been hard to start, but always ran great once started.

A while back, it began to have an intermittent problem where it would only run at partial throttle. Idled fine, pat throttle okay, but open it up all the way and it died. And at part throttle, of course, it didn't have much power for cutting. Now it has started doing this all the time.

I cleaned the air filter, changed the plug. No help. I didn't have a spare fuel filter, so I ran it for a bit without the filter and it was no better. There seem to be no adjustemnts on the carb. Any ideas what could be wrong?

Thanks.

 

[usmarinekurt]

Muffler screen?

 

[Stihl-Pioneer]

It sounds like you have either a plugged muffler screen or some junk in the carb.

 

[caricob]

+1 on the muffler screen

 

[MechanicMatt]

Hey greycephenil, ask the marine how he knows about the muffler screen. I hope I spelled your name right. The devildog had a all too similar post today, he found his screen plugged up bad. Clean it up and she'll run like a champ, if its not the screen Id suggest getting a adjustable carb for it. Im on the look out for one myself for my 025. My saw runs good, just like being able to "screw" around.

 

[sheepsmoke]

also check choke spring...got one for free a while back choke spring was broke so when you opened her up choke would pull shut and she'd die

 

[graycenphil]

Thanks guys. I did clean the muffler screen too, no help. I'll check the choke and if that doesn't work, take off the carb and clean it out. Anything tricky about the carb? Is it okay to blow it out with compressed air? And what adjustable carb would fit on this motor?

 

[russhd1997]

I have been told that a carb from an MS210 will fit and is adjustable. There are also adjustable carbs on feebay for about $25 but they are made in China and I don't know about the quality.

 

[WVwoodsman]

Your saw seems pretty new, but do you have a way to check to compression? My Ms 310 was exhibiting similar characterisitcs such as you have described and upon checking everything that was listed above, I finally checked the compression and found it to be 110 psi and slowly dropping. After pulling the muffler, I found a scored piston. You may want to pull the muffler and check if you don't have a compression gauge.

 

[Fish]

You likely just need to go correctly through the carb and clean it out with carb spray. Remove the needle/spring and visually make sure that
the passage under the needle is clear by holding it up to a light.

Also, look at the fuel line closely, above the tank, it is prone to develop cracks, in the tank, the fuel line can get soft and gummy.

 

[graycenphil]

Thanks again. What a great forum.

 

[graycenphil]

I finally got to it yesterday. Pretty hard to get apart, it's so tight in there. But I pulled off the carb, sprayed the heck out of it, dried it out, got it all back together and it runs like a champion.

Thanks again to everybody.