OT:Stihl MS 170 saw

Phil9N3667

Well-known Member
Haven't been here in a while to post/respond to messages, but I've got a hair puller!! My MS170 Stihl will start/run at fast idle, but starves for fuel/won't go to high RPMs. Cleaned the filter, replaced the pickup/fuel line, disassembled and cleaned the carb out best I could. I call myself a mechanic, but this one's got me bamboozled! No amount of adjustment on the high speed (?) jet makes any difference. This screw has LH threads!! Any Stihl gurus out there!? Thanks in advance for any advice!!
 
In my opinion only,you still have plugged orifice due to ethanol gas.
I use spray carb cleaner and cutting torch tip cleaner carefully ,so you don't break it off
Stihl recommends HI TEST gasoline with oil mixture for their 2 cycle engines
 
Had that same problem and went thru the same process. Took it to the shop. The diaphragm was the problem.It was cheaper to buy a carb verses rebuild.Less than 25.00 .Good Luck.
 
I have the same saw. Had trouble like that, remedy was a choice of either a difficult carb rebuild, or for a few bucks more a new carb. I got new carb. NOte, make sure the carbon on the exhaust screen is all completely burned off, with a propane torch. Will not run otherwise.
 
Thanks, guys. I'll see what a carb goes for and maybe go back through it a bit more thoroughly with carb cleaner, wire drills and a piece of tag wire where possible. I don't use a saw nearly as much now as I used to when I burned wood and the ethanol gas wasn't an issue either. Have a good week, folks!!
 
Tank vent clear? My 021 ran like yours, it would start right up, but, it would also never start again once you shut it off to put gas in it. I tried cleaning that carb about 5 times, my dad tried twice after I gave it to him. I was in the Stihl dealer getting parts for something else and asked him about it, he said don't even waste the time trying to clean the carb, just throw a new one on there, it'll be fine. So that's what dad did, bought a new carb, $23, put it on and it runs like it never had a problem.
 
Had the same problem with a new Echo commercial hedge trimmer. Was only used twice and less than 5 hours. Took it back to dealer and said it wasn't under warranty as it doesn't apply to carbs and the only solution was to buy a new carb. Did some research and it is a known problem with the new epa rules on emmissions. The cause is a the passage ways are extremely small and any debris, sludge, or ethanol gup will clog the "needle". At the top of the carb under the primer bulb is a "secret passage port" with a small plastic plug. Under the plug is locking plug that has to come out to get to the needle orifice. I used a sharp pick to remove the plastic plug, a drill bit to remove the plug and small flat head screw drive to get the needle out. I cleaned out the needle passage with a small wire I got off a drill wire brush. Do not drill very deep on the blocking plug or you could damage the needle. After cleaning out the needle, and reassembling, it worked great. I ordered a new carb for $20 off internet to have as a spare. Go to YouTube and there are several videos that show the procedure. You can thank the EPA and ethanol lobby for this common problem. I have started using the non-ethanol fuel mix you can buy in a can which does not have any ethanol for all my two cycle engines. More expensive but a lot less problems, especially on chain saws and anything that has fuel lines or carb seals and orifices.
 
That's exactly what I encountered...#15.00 for varb rebuild kit or #25.00 for new carb. I chose new carb plus cleaned the exhaust screen.

Works like new.
 

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