The screw at the bottom is the main jet needle valve.

Tecumseh carbs have three adjustments: idle speed which will be a screw
possibly with a spring wrapped around it, that sets how far the throttle
plate can close off the fuel/air supply; a low speed needle valve which is
often located on top or on the side near the throttle shaft, and a high
speed or main needle valve located under the fuel bowl.

The low speed (often called idle mixture) needle valve is adjusted for
maximum RPM at idle. This is usually about 1-1/2 turns from fully tightened.
Turn it slowly each way, noting where the engine runs rougher or slows down,
then set it in the middle. Do this adjustment first.

Second would be to set the idle speed. This is often around 1800 for rotary
mowers but could be slower for tractors, i.e. 1200 - 1400 RPM. If you make a
significant adjustment here, go back and repeat the idle mixture adjustment.

Lastly is the high speed mixture. Set the engine at idle speed, then set it
to full throttle using the main speed control. Do NOT use a finger to
manually open the throttle at the carburetor as the engine is governed and
should limit its speed to around 3000 RPM. Adjust the mixture so the engine
accelerates without hesitation or backfiring. This will take several tries,
and is also usually around 1-1/2 turns from fully tightened. Usually it will
only take a change of 1/4 to 1/2 turn to get it to smoothly accelerate. You
can do this under load as well. Clockwise will result in a leaner mixture,
i.e. less fuel compared to the air going through the carburetor.

None of these adjustments should be way out unless someone pulled the valves
out to clean the carburetor and didn't pay attention to where they were set
beforehand. If you do need to pull them out, carefully turn each one in
(clockwise) and count how many turns it takes until it seats fully, but do
not exceed that position, then remove it and the spring. Some needle valves
also have a rubber O-ring and even a flat washer at the end of the spring in
the casting, so be careful.

These procedures are most likely outlined in the several good books on small
engine repair. A trip to a local library might give you more detailed
information. I'm going from memory as I usually make the adjustments without
even thinking about them.

Good luck.
Bob
====
"Buck Wheat" wrote in message
om...
That's exactly what I needed to know, I tried several positions
yesterday w/the float bowl, all yielded the same result...no change,
I'll correct it today. I was able to cut the lawn as once it is in
full throttle it doesn't seem to oscillate.

What does the screw/adjustment at the bottom of the float bowl do?

Thanks.

"Bob M." wrote in message
...
If it's a Tecumseh engine, and there's a flat area in the fuel bowl,
this
goes directly under the hinge area of the carb, so the float can drop as
far
as it needs to.

Bob
===
"Buck Wheat" wrote in message
om...
Actually, it would not start about a month ago, so I took the bowl off
and cleaned out the carb and hoses. I had to turn the bowl little by
little to get it started again, I think maybe the bowl is still not
correctly positioned.

I'll take it off and try to find the right position, I have not seen
any markings to line-up..if there are any(?) I'll check all other
parts for clogging, etc.

Thanks for taking the time to reply, it's a riding mower and I dread
trying to get it to the shop.


"Dr. Doctor" wrote in message
news:qpWYa.14434$%T.3973@edtnps84...
hunt or oscillates can be the spring but in all my years of working
and
teaching on small engines it is not a common failure. there is a
list of
possible here is but a few, air filter plugged, worn throttle shaft
carb,
intake manifold leaking, governor problems (worn or misadjust)
linkage
worn
bent or missing, fuel problems.

as I said the list is long but when one runs into a problem with a
spring it
is more common it will either be stretched and the rpms are too low
or
modified some how and has too much tension making rpms too high.

good luck