# stihl weedeater 4 mix prob



## nobrakes (Jul 26, 2008)

i have a fs 100 rx 4 mix idles fine but when you hit full throttle runs really rough you can run it about 5 or 10 minutes then it will smooth out.I have rebuilt carb all fuel lines are in good condition checked port and screen no build up at all engine is really clean no leaks on head checked while at wot sprayed with starting fluid around all bolts no change in how it runs also when i tried adjusting the fuel adjusting screws there was no change except how it idled i am wondering can the valves have any thing to do with this if so how would i check them had the cover off they seem fine but i dont know that much about valves on a weedeater any help would be appreciated 
and if not the valves what else can it be? thanx guys yall are always helpful


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## geogrubb (Jul 28, 2006)

It probably needs a valve adjustment, if you google "valve adjustment for stihl 4 mix" you will get a lot of hits. Have a good one. Geo


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## paulr44 (Oct 14, 2008)

OEM setting is .10 MM, or about .004"
Does it throttle up okay? As for vacuum leaks, the 4-mix's we get in when they're 2 to 4 yrs. old often need a recoil-side crankshaft seal - spray carb. cleaner down in there when running it. Seen some run (poorly) with sheared flywheel keys, which are built into the flywheel.
Paul


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## nobrakes (Jul 26, 2008)

checked all bolts no change in how it runs {and seals} im gonna try adjusting valves if that dont work ill check fly wheel key 
thnx for the help will keep you posted
Jo


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## paulr44 (Oct 14, 2008)

Just a thought - you said it eventually cleans up. If it's a newer style, the fuel tank vent hose is connected to the air cleaner housing - if the vent is bad, it may be wetting the air filter once shut down, and once enough air passes through the mixture gets lean enough to smooth out. Easy to check - test run without air filter.


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