I have a 40 year old Stihl chainsaw that is giving me fits.
It had not been used in probably 6 months or more.
Even back then, it was having problems, with not wanting
to start, stalling when going back to idle, etc.
I got it running this time and after fooling around with it
was able to actually use it to cut up one large tree. It
usually will eventually start from cold, after a lot of
fiddling between choking, not choking, etc,
but then has trouble transitioning
to full throttle. It won't idle, it stalls if you try to let it
But at full throttle, it ran OK and cut like a champ. You
just can't let it go back to less than maybe 1/4 power or
it stalls out. I also observed gas dripping from the carb
at times. And at times after it's run, it's very difficult to
I took the Stilotson carb apart and it all looked good, except for
a small fuel screen in the carb. It was packed with gunk. Otherwise
it looked good, no rust, no other signs of fouling. I cleaned it
out with carb cleaner, compressed air, put it back together.
I ordered a carb kit and took it apart again today. Cleaned it
again with compressed air, including this time I could take out
the welch plug. All the passages look like brand new. The
kit included two new diaphrams that form the fuel pump,
new needle valve, gaskets. etc. The old diaphrams
were still intact, but they\had more stretch/play then
the new ones. Was hoping this was the problem. Put it
all back together again, following the service manual, so I'm
pretty sure it's right. Still same problems.
Tried squirting a bit of fuel into the carb directly and it fires
right up. Did that several times. Without the squirt, it's much
harder to start.
I've taken it apart to inspect the fuel line to the tank and filter
which is inside the tank. I can suck or blow on the line,
pinching off the filter end and no evidence of any air leaks.
Fuel filter is clean.
I put a new plug in and also have tried pull starting it with
the plug out, but connected. Good spark. Also when taking
the plug out after having tried to start it for a long time, the
plug is dry. Acts like it's not getting fuel....
So, from a bit of searching, it looks like one of the other
potential problems is the impulse line. This carb uses a
line from the crankcase to supply alternating pressure
and vacuum that works the fuel pump diaphrams in the
carb. Apparently if the crankcase seals are kaput, then
it may not get enough pressure/vacuum. I've inspected
the hose, it looks OK. With the sparkplug out and pulling
the starter, I can feel some suction, some puffing on the
end of that impulse hose with my finger. But not a lot.
Anyone know how much you should be able to feel?
Or have any other ideas?