I have a Stihl S10 top handle with a HL 166B carburetor. Saw has compression of 140. Saw starts,idles and revs but while doing this fuel will come out past the choke butterfly and run into the air filter. Anyone have any ideas what is causing this.
Stihl S10 fuel issue
- Thread starter Oldengr
- Start date
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Two things I can think of that cause this condition is the carb is slightly flooding from some internal problems and or the intake skirt of the piston is getting worn out. Others will be along to give their versions.
Good info thanks. I will start with carburetor. Piston may be more difficult as this S10 is an early 44mm not the later more common 47mm.
Just another note, the intake side of a piston wears out faster than the exhaust side so looking in through the exhaust side with the muffler removed will not tell the whole story. Lets hope the carb diaphragms are just hardened up and are holding the metering needle a bit off its seat.
1hander
ArboristSite Operative
at 140 id say your piston is still healthy
its a carb problem
i was having the same issue on one if mine..
its flooding..through the high speed jet
when its running at part throttle its running on the low speed jets...
and the check valve has 1 atmospere pushing up on it and is closed
which shuts off fuel flow to the high speed jet
as you increase throttle, the throttle plate opens,
then atmosphere equalizes on both sides of the throttle plate
which allows the check valve to open and the high speed jet becomes active
as i understand it LOL
buuuutttttttttt either
1. the diaphragm is holding the main metering needle open cuz its no good anymore , wrinkled, deformed, hardened
2. the metering spring is too weak to hold the needle shut between crank pulses...so it just pours fuel to the high speed jet
3. theres some debris stuck in the main metering needle and not allowing it to close..
try to adjust the high speed needle, if its one of the above, the H needle will be almost useless, youll have to almost completely close it
to stop the fuel pouring out the back of the carb
sometimes if you let the carb sit with fuel in it, the diaphragm will soften back p again, but its a good sign she needs rebuild
im betting on the diaphragm or the spring
its a carb problem
i was having the same issue on one if mine..
its flooding..through the high speed jet
when its running at part throttle its running on the low speed jets...
and the check valve has 1 atmospere pushing up on it and is closed
which shuts off fuel flow to the high speed jet
as you increase throttle, the throttle plate opens,
then atmosphere equalizes on both sides of the throttle plate
which allows the check valve to open and the high speed jet becomes active
as i understand it LOL
buuuutttttttttt either
1. the diaphragm is holding the main metering needle open cuz its no good anymore , wrinkled, deformed, hardened
2. the metering spring is too weak to hold the needle shut between crank pulses...so it just pours fuel to the high speed jet
3. theres some debris stuck in the main metering needle and not allowing it to close..
try to adjust the high speed needle, if its one of the above, the H needle will be almost useless, youll have to almost completely close it
to stop the fuel pouring out the back of the carb
sometimes if you let the carb sit with fuel in it, the diaphragm will soften back p again, but its a good sign she needs rebuild
im betting on the diaphragm or the spring
