It has an idle air/fuel mixture screw -it's on the LH side of the carb at about a 45 degree angle to the venturi located near the intake side of the carb - it intersects the hole on the left in your pic - it adjusts the amount of air let into the idle circuit - setting is simple - on a two stroke, 1 1/2 turns out from lightly seated is usually adequate unless someone has drilled out or changed the pilot jet to allow more fuel in (more fuel is more power, right? WRONG! - more air is more power - that's why turbo and super chargers were devised)
The hole in the middle at the bottom is the air passage to the emulsion tube to allow air to mix with raw fuel atomizing it before it enters the venturi - the hole on the right (deeper inside the mouth of the carb) is the air passage to the enrichener (electric choke) - the operation of the enrichener is this: it is open (allows fuel and air to bypass the slide allowing fuel rich air into the intake for easier starting) whenever the engine is not running - the enrichener is connected to one leg of the alternator so when the engine starts, AC current passes through the coil of the enrichener unit - this causes the coil to heat (the heat causes a gas in a small cylinder to expand or a bi-metal spring to move) pushing the enrichener plunger down closing the port and the fuel jet. This takes about 30 seconds to a little over a minute (depends on the design of the unit). To test the operation of the unit, remove it, connect it to a 12 volt DC source and watch the plunger slowly extend downward out of the unit (moves about 1/4 inch - 1/2 inch at the most) thus closing the choke - remove the voltage and it will slowly retract (opening the choke) - if it does this, it is working correctly.
Shop Owner and Mechanic with over 50 years experience