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#Post#: 89587--------------------------------------------------
Clone saw carbs a cheap troublefree substitute , on brushcutters
By: joe_indi Date: October 26, 2022, 1:17 am
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The problem with most OE carbs for brushcutters are they are
designed to run very lean and chances are they get out of order
rapidly at times.
I had a couple of Stihl brushcutters, FS 55, 85, 120 200 all
with carb issues that customers abandoned because of carb
replacement.
So i had a carb of a clone saw and had the bright idea to try it
on a FS 55.
So serious ( initially) modification was required. But once you
know your way around it, it's not such a big issue.
The first issue was the impulse. On the saw carb the impulse is
connected through a tube. But the mold of the pump section has
the areas for the internal impulse and all that has to be done
is drill holes or cut paths, and block off the connector ( i
removed the connector and plugged the hole)
Checking whether the new impulse works is simple. Remove the
metering diaphragm, tighten the carb onto the engine, with spark
plug removed and metering lever pressed pull the starter. If
impulse works the fuel is pumped out. I then closed up the
metering chamber and primed the cylinder and started up. Started
first shot. But setting L and H is not too simple because the
fuel delivery is different between a saw and a trimmer. But once
you get it right it really works and with oodles of power
potential! So i opened up the muffler a bit , filed of a bit of
the exhaust port to slightly advance the timing, and , that FS55
became a different animal altogether!
So, i did it again on another FS 55 and a third!
Then i thought if it can be done on a FS55, why not the old FS85
i had, worked great. So i tried it on a FS120 still great and so
was the FS200.
The obstacles ( i saved for last) changing the throttle shaft
and in the case of the FS 120/200 the choke shaft. Some careful
vwork with a round file is needed , that is all,but the efforts
are worth it. One issue i had was on the 55 and 85 i had to do
without the primer that sits on the carb. But, old Stihls like
my FS160 never had one. An extra pull or two are all that are
required . I made the mistake of trying a 3 tube carb of a saw
that has priming option. I tried it on the FS120. Other than
pumping up the fuel into the carb earlier that primer sticks
like a sore thumb because it plays hell with the tuning. So i
decided to eliminate the primers. Fuel consumption has not
increased, but the power delivery is much better. The biggest
surprise was the 55, it's like a little monster in its all out
form.
In case anyone is hooked i could upload videos to my Google
drive and post the links here
Also photos
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