Hey, Mike --

The very first thing you need to know about carburetors is that it's a French
word. Translated, it means "Don't mess with it!" No matter what your opinion
of the French may be otherwise, you have to admit that they mostly got it right
with this one!

Seriously, this carb adjustment thing is a whole lot easier than it's being made
out to be. And for the past forty-years, it's been pretty much the same for
every make and model out there ...

The overwhelming majority of all chainsaws that have ever been made, (well, at
least up to the past few years or so -- because some of the latest models of
saws are coming with fixed jets that you CAN'T adjust, thanks to the EPA!), have
only three possible external carburetor adjustments you can make:

1) Idle Speed -- a mechanical stop that holds the carb's throttle butterfly open
a crack and is adjustable to allow you to admit just the right amount of
air/fuel mix to make the saw idle at just below the chain-engagement speed.
2) Idle Mixture -- a needle-valve that will allow you to adjust the air/fuel
mixture within the idle speed-range.
3) High Speed Mixture -- a needle-valve that will allow you to adjust the
air/fuel mixture covering the range from just above idle to wide-open screaming.

Before I start, lemme preface what I'm about to tell you with this: 1) this is a
very predictable sequence with a saw that has all its mechanicals in good order.
All bets are off, however, when your case seals are leaking, or your carb is
clogged with varnish or stale fuel or sawdust, or where your ignition is
acting-up along with about everything else, and 2) these procedures will work
for probably 99% of all the saws out there. I am, however, willing to
acknowledge that there may be a newfangled carb design out there -- somewhere --
that requires the needle-valves to be screwed IN to enrichen the mixture (like
some Weber carbs for automobiles). So, in the unlikely event that these
procedures DON'T work for you, I'd recommend that you 1) invest in a shop manual
for your particular saw, and/or 2) seek professional help.

Time to relate a favorite old adage: "If, at first, you don't succeed -- try,
try again. And, if you stihl don't succeed -- try reading the instructions.
And, if you STIHL don't succeed -- try following them!"

Anybody NOT understand this?

Ok, here goes ...

In a nutshell (or maybe a small bowl of nuts worth of nutshells), here's how
it's done:

1) Saw Prep:

Fresh gas & oil (see Epilog-2, below). Clean your stinkin' aircleaner, clean
and gap your sparkplug, and have your bar and chain properly installed and
adjusted. In other words, give yourself a fighting chance before you invest a
whole bunch of blood, sweat, and tears -- only to find out that all it was, was
a fouled plug.

For instance -- I did a quick tune-up on a co-worker's 038 Magnum in the woods
over the weekend and couldn't get the stoopid thing to respond to the idle speed
adjustment -- idle was way too high. It turned-out to be a wad of sawdust
lodged under the idle-stop arm. So, while you're there, a quick visual
inspection of the area around the carb while the aircleaner is removed isn't a
bad idea!

2) Start the saw and give it a minute or two of running to warm it up a bit and
get the FRESH gas running through it.

3) Adjust the idle-speed throttle stop for an idle that's just under the
chain-engagement speed -- if possible:

It's the screw labeled "LA" for "Laufende" on the Stihls -- the German word for,
well, "idle". For many others, it's the third adjustment screw -- the one that
ISN'T labeled either "L" or "H" (or maybe anything!). If you can get an eyeball
on the carb, you're looking for an adjustment screw that doesn't just disappear
into the side of the carb -- THOSE would be the mixture screws -- but, rather,
impinges against the throttle mechanism somehow. If you can get the saw to idle
just under the chain engagement speed, then you're mostly over the hump. If
not, then get it as close as possible without killing it.

4) Now adjust the low (or idle) jet:

It's the screw labeled "L" on the Stihls and almost all others. Don't ask me
why Stihl didn't label it "T" for "tief" -- the German word for "low" -- I don't
know. Anyway, you want to peak out the rpms with this adjustment -- make the
saw idle as fast as you can by gently and slowly screwing this needle-valve in
or out -- while the saw is idling. Then go back to the idle-speed adjustment
screw, and back the rpm's down to just under chain-engagement speed again. And
then go back and do the idle mixture peaking again, (and maybe again, if your
saw's carb was waaaaaay out of adjustment). You want the idle mixture to be
optimized at that just-under-chain-engagement speed. If you've done this
correctly, your saw is idling at a near perfect air/fuel ratio (~14:1), but will
die if you goose the throttle. Don't fret -- this is right where you want it to
be ... but only temporarily. Next, you need to richen the idle mixture up just
a bit to enable the saw to accelerate smoothly when you goose the throttle from
a stable idle.

With the mixture set at 14:1, the saw will hesitate when you snap the throttle
wide-open (and die, if you're not quick to release it), rather than accelerate.
To correct this, OPEN (un-screw) the "L" needle-valve maybe an eighth to a
quarter-turn. This will richen the mixture slightly and may cause the idle to
drop down a bit as well, so you'll probably have to re-adjust the idle speed
back up to just under the engagement point again. Snap the throttle open again.
If the saw takes-off without hesitation, then you're there. If it stihl
hesitates, then you need to richen the mixture up just a bit more. You are
aiming for an idle mixture that's JUST rich enough to allow for a good
acceleration -- but no more (unless you want to have your plug foul while the
saw is sitting there idling). And, once again, you want the idling speed to be
set just under that chain-engagement point. This completes the idle stuff ...
at least for the moment.

If your settings are so messed-up that idle isn't possible, then you can go with
the high-end adjustment first and come back to mess with the idle, second.
There's no absolute rule that the idle has to be set first ... it's just that in
some carbs the idle adjustment can mess with the high-end one a bit, and
verse-visa, depending on the carb's internal design. That, and the fact that
it's usually a whole lot more convenient to quickly get the saw to the point
where you don't have to continually fight to keep the stinkin' thing going on
it's own, while you paw around in your toolbox for another screwdriver (or
whatever) to continue the process.

5) Next, we're gonna adjust the high-end (Main) jet:

This one is the screw labeled "H" on the Stihls and almost all others. In this
case, "H" not only works for the German word "hoch", but also for the English
equivalency -- "high". The idea here is to peak-out the rpms, (we're going for
that theoretically perfect ~14:1 mixture again) and once we're there -- with a
screamin' saw -- then we're gonna back the needle-valve out to richen the
mixture to approximately the twelve (or maybe thirteen):1 range -- and we're
gonna do that by ear. A saw running at wide-open throttle at 14:1 is a screamer
with a "pure" exhaust note. When you back that jet out an eighth to a quarter
turn (or maybe a little more or less, depending on your particular saw/carb),
you're gonna hear the tone change -- and I'm not just talking about the pitch
(rpm) which is also gonna lower a bit -- I'm talking about the exhaust tone JUST
taking on a "warble" or maybe a "dual-tone" kind of sound. If you play with the
mixture setting at full throttle for a moment or two -- up and down -- from a
perfect to slightly (or a little more than slightly) rich mixture -- you'll hear
what I'm talking about. Incidentally, hearing protection isn't a bad idea while
you're fooling around with this carb adjusting stuff. In fact, I believe it
allows you to hear what's going on more clearly. Once you've backed that high
jet out to where you can hear the "warble" -- and I don't mean "'MAYBE' hear the
warble" -- you're done with the top end ... but for possibly rechecking it if
you have to make much movement in your original idle settings, via step 6 below.

I've got to add here that this high-end adjustment is the most critical one of
all those that you're making. The health of your saw is totally dependent on
you doing this one right -- as the couple of recent confessions from our more
adventuresome colleagues about fried saws will testify to.

Three things are happening when you set that full-throttle mixture to a perfect
14:1, UNLOADED ... and then further lean it out by putting the saw under a load:
1) the piston & cylinder temperatures skyrocket, 2) there's less cooling effect
provided by the evaporation of the less fuel(/oil) volume in the flow, and
(probably most importantly) 3) you're simultaneously providing less lubrication
because you're providing less (fuel/)oil per volume of air in the mixture. It's
a triple-whammy that can probably be endured indefinitely for the kind of usage
you might put your smaller saws to when, for instance, you're pruning a small
orchard tree -- you know, small little blips of the throttle with long periods
of idling in between ... but which will be the "kiss-of-death" for a large saw
doing that fifteen-minutes of full-throttle running in an Alaskan. You got me?
And this would be primarily why I spike my fuel/oil mixture a bit for my
big-dogs when they're pulling an Alaskan -- just to make sure there's a little
more lube in there than I REALLY need.

6) And finally, go back and recheck the idle settings, just in case the high-end
adjusting has changed things a little bit, down low.

You're done! Now, wasn't that easy? Once you've got the concepts down and have
done this a few times, it'll take you maybe a whole minute to tweak just about
any saw back into proper behavior.

Epilog 1: If your carb has been totally messed with (refer back to the origins
of the word "carburetor", above), and your needle-valve settings are all kinds
of goofed-up, you can fall back to the manufacturer's recommended initial
needle-valve settings. They vary from one make of carb and saw to the next, but
usually only slightly. Most of them will start you out with 1, 1 1/8, or maybe
1 1/4 turns open from GENTLY closed. And a few of them will have you in the
2-turns range for that initial set-up. Keep in mind that these are only the
STARTING settings -- the fine-tuning procedures will add-to or take away from
these, depending on a host of variables ranging from age and wear on the saw,
thru atmospheric conditions (altitude, temp, and moisture), to the stuff you're
using for your fuel and oil. These initial settings are ONLY designed to give
you a fighting chance to get the stinkin' saw running. The fine tuning begins
there.

Epilog 2: And lastly, lemme put in a shameless plug for that incomparable Opti-2
oil @ 75:1 in either Texaco (now Shell, out my way) or Chevron 92-octane (no
stinkin' gasohol!!!), and Ralph -- a fellow wood-miller who you can both trust,
and order the stuff from if you can't find it locally.

I'm out of here, guys -- hope this helps.

LumberDennis



(I'll take my kick-back later, Ralph --- JUST KIDDING, just kidding ... :-o




-----Original Message-----
From: william(Bill) M. Cowart <wmcowart@...>
[mailto:wmcowart@...]
Sent: Monday, January 20, 2003 6:56 AM
To: milling@yahoogroups.com
Subject: [milling] Re: Opti 2, carb adjustment , be careful


After our ice storm a couple yrs. ago, there where a few saws for
sale cheap here, so I answered a cheap add. The saw , a larger poluan
had no chain oil , and I suspect very little oil in gas,; but I
bought, and it ran good. I used it for slabing with a lumber maker.
It seemed to be heavy and unbalanced in comparison to Sthil, but
preformed very good. When it started running slugish,I leaned it out,
WoW , did I lean it out, and it ran like a stripped ape. Two
problems, first I leaned it tooo much, next the poluan alumun cyl.
liner just was not designed for lean runing like my carb ajustment
demanded. End results. one seazed saw. Bud tells me he can get me a
crome liner for arround $125, I might fix some day, maby. Mortal
Point, be carefule when leaning out your saw. --- In
milling@yahoogroups.com, "cochrandaniel <cochranmike@i...>"
<cochranmike@i...> wrote:
> My old Stihl 028 runs rough with Opti 2. My Husky runs great with
> it, made no adjustments. Mixing 75:1, how should adjust carb to
make
> it run smoothly. Have new fuel filter. Mike




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