On Nov 17, 5:15*pm, wrote:
On Sat, 17 Nov 2012 13:56:59 -0800, Oren wrote:
On Sat, 17 Nov 2012 13:25:34 -0800 (PST), "
wrote:

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
idle.
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
start again.

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.
Same problem.

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?

No expert but a couple of thoughts.

1) Tip of a High/Low adjustment screw is bent
2) Screws not adjusted correctly
3) If the body has a venturi it can be clogged - clean the passage
with a SS wire plucked from a wire brush (DO NOT BREAK WIRE)
3) Soak the carb overnight in a carb cleaner

HTH

* Make SURE the crankshaft seals are good. If they leak the engine
runs lean - more noticeable at idle - and is hard or impossible to
start. 2 stroke engines are VERY fussy that way.- Hide quoted text -

- Show quoted text -

From where I've been so far, that seem like one of the
posibilities left. Only problem is, how can you tell if
they are leaking or not? The service manual has the test
procedure, which boils down to removing the carb,
removing the muffler, bolting a testing adapter where
the carb was, bolting a blocking plate over the exhaust,
getting the piston to TDC, then applying pressure and
vacuum to the test adapter, therby pressurizing
the crancase, to see if it holds about 7 psi.

Only problem is, I don't have the test adapter or blocking
plate. Not sure much can be determined by finding the
seals and looking at them. And by the time I'm there,
might as well just replace them. Any ideas on another
way to test?