Scheme of the carburetor idle system
1 - throttle body; 2 - throttle valve of the first chamber; 3 - openings of transient modes; 4 - hole, adjustable screw amount of the mixture; 5 - air supply channel; 6 - adjusting screw for the amount of the mixture; 7 - composition adjusting screw (quality) mixtures; 8 - emulsion channel of the idle system; 9 - adjusting screw for additional air *; 10 - cover of the carburetor body; 11 - air jet of the idle system; 12 - housing of the idle fuel jet with a shut-off valve; 13 - fuel channel of the idle system; 14 - emulsion well.
* Installed on parts of carburetors.
The idle system is adjustable to provide a stable engine idle speed with a minimum amount of carbon monoxide (SO) and hydrocarbons (CH) in exhaust gases. This operation is recommended to be carried out at the adjustment points «CO-CH».
To adjust the idle speed, the carburetor has a quantity screw that reduces or increases the amount of mixture entering the engine, and a quality screw that determines the composition of the mixture (see Design Description).
At the factory, restrictive plastic bushings are pressed onto these screws.
They do not allow you to violate the factory settings. The mixture quantity screw with a restrictive sleeve can be turned by no more than 90°, and the quality screw by 50°, which allows, without a gas analyzer, only to adjust the idle speed. If it is not possible to adjust the idle speed with the bushings, break them with a screwdriver and repeat the operation.
We carry out the adjustment using a gas analyzer on an engine warmed up to operating temperature with adjusted ignition and clearances in the valve drive (see relevant sections), with the air damper fully open.
Using the quantity screw, set the crankshaft speed to 820–900 min using the tachometer–1.
Use the quality screw to achieve the concentration of CO in the exhaust gases within 0.5–1.2% at this position of the quantity screw.
Use the quantity screw to restore the crankshaft speed to 820–900 min–1. If necessary, use the quality screw to restore the CO concentration to 0.5–1.2%.