Small Engines (Lawn Mowers, etc.): Toro snow blower, toro snow blower, throttle shaft

Question
I have a Toro snow blower CR20.  It is old but works well when tuned.  It is a 2 stroke, I put a gas oil mixture.  I have lost my manual which shows how to tune it up.  There is a 3 position switch on the machine, I turn it to the right most position when cold.  When it warms up, I am supposed to turn it to the middle position, and then to the top position.  Now, when I turn it to the middle position and top position even when warm, it stalls.  Also, after running for a while, it stalls.  There is no throttle on this snow thrower.

I want to adjust the carb so that it runs well.  There are 2 screws on the left side of the carb, one above the other.  I don't remember which one is the idling speed and which is the mixture.  How do I tune this?

It is possible that there is something else that needs to be done?  I took it in a few years ago to have it tuned, the mechanic said that he replaced some kind of filter, but there is no filter between the gas tank and the carb.  This machine sees use only about 3 - 6 times a year.

One further question, what it the ratio of gas to oil?  I seem to recall that it is 32:1.  Am I right?

Do you have any suggestions.

Many thanks,
Sol, Ontario, Canada.

Answer
32:1 should be fine.  The filter may have been a spark arrestor or inside the carb.

On older 2 strokes carbon/oil will build up and restict the muffler.  Remove the muffler, check for a spark arrestor screen and clean the muffler, spark arrestor and the engine exhaust port.

For the carb adujustment you need to carefully look at the needles.  One screw is for the idle.  You will see the screw end that keeps the throttle shaft open for idle.

The other needle should go inside the carb.  Try turning this needle out while the engine is running full speed.  From what you described the engine is running lean.   Turning the needle out should richen the mixture if it is a high speed adjustment needle.  If there is no change in engine performance then the needle is an idle fuel/air adjustment.  You should not have to turn the needle out more than 1/8 turn.  If the engine still needs the choke on to run then more than likely the carburetor diaphragm and gaskets need to be replaced.

Let me know what you find.
Eric