I just bought a one man Earth Auger at a local auction. (power post
hole digger).
The thing is old, but for $5, I decided to give it a shot since these
things are over $350 new.
It has a Tecumseh 2 cycle engine - power head.
After spraying carb cleaner thru all the carb ports, I got the engine
to run but it's runs very rough. I think much of this has to do with
the carb adjustments. The problem is that I dont know which screw
does what or what the initial settings should be (other than what they
were, which I wrote down).

It's a 3HP Tecumseh 2 cycle engine. There is a large screw and a
smaller screw. They are next to each other.
Does anyone know anything about adjusting these?
I repair lots of 4 cycle engines, but am not very familiar with 2
cycle engines.

The initial settings that it had was approx. 2 1/2 turns on each
screw.

Is there a standard meaning for small screw and large screw, or is
this just this particular model?

An additional mention. This thing has no name or model number. Just
says Tecumseh 3hp on the engine, so I am not sure if the whole tool is
made by Tecumseh, or just the engine. This will make it real hard to
ever get any parts or a manual for it. From the looks of it, I
suspect it was made in the 1970's or 80's.

Thanks

Mark

There is a large screw and a
smaller screw. They are next to each other.
Does anyone know anything about adjusting these?

One, probably the larger one is the high speed adjustment, the other
the low speed. It gets a little more complicated than that, as they
interact. Changing the high speed effects the low speed. You just have
to get it running good wide open then try for a decent low speed/idle,
then do it all over again till both seem about right. better to end up
a little bit rich than a little bit lean.

"Eric in North TX" wrote in message
oups.com...


There is a large screw and a
smaller screw. They are next to each other.
Does anyone know anything about adjusting these?

One, probably the larger one is the high speed adjustment, the other
the low speed. It gets a little more complicated than that, as they
interact. Changing the high speed effects the low speed. You just have
to get it running good wide open then try for a decent low speed/idle,
then do it all over again till both seem about right. better to end up
a little bit rich than a little bit lean.

If one screw is closer to the engine cylinder, that is usually the low speed
mixture control. If one screw is in the center of the carburetor, that is
usually the high speed mixture control.

Be sure you have a good spark plug and that the exhaust ports and muffler
are not clogged. These are very common causes of two stroke engine problems.

Don Young

According to Eric in North TX :


There is a large screw and a
smaller screw. They are next to each other.
Does anyone know anything about adjusting these?

One, probably the larger one is the high speed adjustment, the other
the low speed. It gets a little more complicated than that, as they
interact. Changing the high speed effects the low speed. You just have
to get it running good wide open then try for a decent low speed/idle,
then do it all over again till both seem about right. better to end up
a little bit rich than a little bit lean.

The instructor of our small engines course said this:

[Presuming idle set screw et. are reasonably correct.]

Start with both needles opened 1 1/4 turns.[3]

Start the engine and get it warmed up.

Rev the engine to full RPMs [1] and adjust the high screw - 1/8 turn
at a time, and find the upper and lower limit of it running best.
Set the needle halfway between the two points.

Let the engine idle, and do the same adjustment trick with the
idle screw. Now, turn the idle screw 1/8 turn _rich_ from the
center of the best running point[2].

Done.

He went to great pains to say "don't touch 'em again" ;-)

At this point you can adjust the idle set screw for what
you want.

[1] You don't do this with chainsaws. High revs with no
load can cause rather bad things to happen if it goes on
long enough. You're supposed to do your high needle adjustment
by full load cutting on a log, tweak the needle, and retest
cutting again.

[2] The 1/8th turn rich on the idle screw is intended to
give the engine a little bit of extra gas to ensure that
the engine doesn't hesitate on quick throttle increases.

[3] He said that when set this way you virtually always
only have to turn the needle one direction to find the
best position. I forget which direction ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris,

Good advise. Especially the part about keeping your hands
off the adjustments screws once they have been properly set.

Should the same advise be offered for snow blower adjustments
that you offered for chains saws: Alwasys tune them under load?

================

Chris Lewis wrote

The instructor of our small engines course said this:

[Presuming idle set screw et. are reasonably correct.]

Start with both needles opened 1 1/4 turns.[3]

Start the engine and get it warmed up.

Rev the engine to full RPMs [1] and adjust the high screw - 1/8 turn
at a time, and find the upper and lower limit of it running best.
Set the needle halfway between the two points.

Let the engine idle, and do the same adjustment trick with the
idle screw. Now, turn the idle screw 1/8 turn _rich_ from the
center of the best running point[2].

Done.

He went to great pains to say "don't touch 'em again" ;-)

At this point you can adjust the idle set screw for what
you want.

[1] You don't do this with chainsaws. High revs with no
load can cause rather bad things to happen if it goes on
long enough. You're supposed to do your high needle adjustment
by full load cutting on a log, tweak the needle, and retest
cutting again.

[2] The 1/8th turn rich on the idle screw is intended to
give the engine a little bit of extra gas to ensure that
the engine doesn't hesitate on quick throttle increases.

[3] He said that when set this way you virtually always
only have to turn the needle one direction to find the
best position. I forget which direction ;-)
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to Gideon :
Chris,

Good advise. Especially the part about keeping your hands
off the adjustments screws once they have been properly set.

Note that he specifically said "don't touch the high speed screw
once you have it set right". In other words, you don't iterate
between idle and high speed screws. Do HI first, then LO, don't
go back to HI.

If you encounter run problems after doing the best job you can,
something else is wrong.

[He identified that the chipper I was trying to clean up and
was difficult to adjust had something wrong with the governor
and it was overspeeding. Turned out a throttle limit screw was
set ridiculously wrong, jamming the linkages and it was drifting
to dangerously high RPMs. You don't want chipper blades coming
off...]

Should the same advise be offered for snow blower adjustments
that you offered for chains saws: Alwasys tune them under load?

No. The issue here is that you normally set the HI screw when
the device is running full throttle, loaded or otherwise. The problem
being with chain saws is that full throttle _without_ load means
that the chain is moving dangerously fast and things may come apart.
Most other devices run full throttle all the time, and don't need
this precaution.

If you have high throttle low load - high throttle high load
issues, there's probably something wrong with the governor. Which
shouldn't be mucked with unless you understand how it works, and
follow a set procedure.

Our instructor really knows his stuff. Early on, he ran a small
engine repair shop. Since that time he became a champion snowmobile
racer (owing perhaps more to his skill with engines than his
driving ;-), and now he's a senior scientist with NRC's wind tunnel in
Ottawa. Testing all sorts of cool things like helicopters, F18s,
cars, and things he couldn't talk about.

Instructing small engine theory and repair is his hobby.

His current job turned out to be quite helpful, after my son took
the course and announced he was trying to make a windtunnel (to
support his rocketry hobby) out of a souped up weed wacker engine.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Thanks

This advice worked out real well on this engine. I figured out which
screw is which too.

Now back to my clutch problem (another posting).

Mark

----------------


On Wed, 09 Aug 2006 03:12:57 -0000, (Chris
Lewis) wrote:

According to Eric in North TX :


There is a large screw and a
smaller screw. They are next to each other.
Does anyone know anything about adjusting these?

One, probably the larger one is the high speed adjustment, the other
the low speed. It gets a little more complicated than that, as they
interact. Changing the high speed effects the low speed. You just have
to get it running good wide open then try for a decent low speed/idle,
then do it all over again till both seem about right. better to end up
a little bit rich than a little bit lean.

The instructor of our small engines course said this:

[Presuming idle set screw et. are reasonably correct.]

Start with both needles opened 1 1/4 turns.[3]

Start the engine and get it warmed up.

Rev the engine to full RPMs [1] and adjust the high screw - 1/8 turn
at a time, and find the upper and lower limit of it running best.
Set the needle halfway between the two points.

Let the engine idle, and do the same adjustment trick with the
idle screw. Now, turn the idle screw 1/8 turn _rich_ from the
center of the best running point[2].

Done.

He went to great pains to say "don't touch 'em again" ;-)

At this point you can adjust the idle set screw for what
you want.

[1] You don't do this with chainsaws. High revs with no
load can cause rather bad things to happen if it goes on
long enough. You're supposed to do your high needle adjustment
by full load cutting on a log, tweak the needle, and retest
cutting again.

[2] The 1/8th turn rich on the idle screw is intended to
give the engine a little bit of extra gas to ensure that
the engine doesn't hesitate on quick throttle increases.

[3] He said that when set this way you virtually always
only have to turn the needle one direction to find the
best position. I forget which direction ;-)