Fuel System Slow and Mid-Range At low speeds engine operates only on slow circuit. As a metered amount of air is drawn through slow air bleed jets, fuel is drawn through main jet and further metered through slow jet. Air and fuel are mixed in body of slow jet and exit to idle progression (transfer port) chamber. From idle progression chamber, air fuel mixture is metered through idle port passage. At low idle air/fuel mixture is controlled by setting of idle fuel adjusting screws. This mixture is then mixed with main body of air and delivered to engine. As throttle plate opening increases, greater amounts of air/fuel mixture are drawn in through fi xed and metered idle progression holes.
As throttle plate opens further, vacuum signal becomes great enough at venturi so main circuit begins to work. Main (high-speed) At high speeds/loads engine operates on main circuit. As a metered amount of air is drawn through air jet, fuel is drawn through main jet. Air and fuel are mixed in main nozzles then enters main body of airfl ow where further mixing of fuel and air occurs. This mixture is then delivered to combustion chamber. Carburetor has a fi xed main circuit; no adjustment is possible. Low Idle Fuel Adjustment Optimum Low Idle Fuel Setting NOTE: Engines will have fi xed low idle or limiter caps on idle fuel adjusting needles.
Step 2 can only be performed within limits allowed by cap. Do not attempt to remove limiter caps. 1. Place throttle control into idle or slow position. Adjust low idle speed to 1200 RPM. Follow Low Idle Speed (RPM) Adjustment. 2. Low idle fuel needle(s) setting: place throttle into idle or slow position. a. Turn 1 low idle fuel adjusting needle out (counterclockwise) from preliminary setting until engine speed decreases (rich). Note position of needle. Now turn adjusting needle in (clockwise). Engine speed may increase, then it will decrease as needle is turned in (lean). Note position of needle. Set adjusting needle midway between rich and lean settings. b.
Repeat procedure on other low idle adjustment needle (two-barrel carburetor only). 3. Recheck/adjust Low Idle Speed (RPM) to specified setting. High Speed (RPM) Adjustment 1. With engine running, move throttle control to fast. 2. Turn inner adjustment screw outward to decrease, or inward to increase RPM speed. Courage singles require loosening screws on speed control bracket and sliding towards carburetor to lower and away from carburetor to increase speed. Carburetor Adjustments NOTE: Carburetor adjustments should be made only after engine has warmed up. Carburetor is designed to deliver correct fuel-to-air mixture to engine under all operating conditions.
Main fuel jet is calibrated at factory and is not adjustable. Idle fuel adjusting needles are also set at factory and normally do not need adjustment. Low Idle Speed (RPM) Adjustment NOTE: Actual low idle speed depends on application. Refer to equipment manufacturer’s recommendations. Low idle speed for basic engines is 1200 RPM. Place throttle control into idle or slow position. Turn low idle speed adjusting screw in or out to obtain allow idle speed of 1200 RPM (± 75 RPM). Governed Idle Speed Adjustment (If equipped) 1. Hold governor lever away from carburetor so throttle lever is against idle speed (RPM) adjustment screw of carburetor.
Start engine and allow to warm up, then adjust screw to set approximately 1200 RPM. Check speed using a tachometer. Turn adjustment screw (inner) clockwise (in) to increase or counterclockwise (out) to decrease speed. 2. Release governor lever and check that throttle lever is in idle position. Turn governed idle adjustment screw to obtain equipment manufacturer’s recommended idle speed (1500-1800 RPM). Some engines have a bendable tab that is used to set this speed. A pliers should be used to bend this tab to achieve recommended speed. Governed idle speed (RPM) is typically 300 RPM (approximate) higher than low idle speed. 3.
Move throttle lever to wide-open/full throttle position and hold in this position. Turn high speed screw to obtain intended high speed no-load RPM. Governed idle speed must be set before making this adjustment. 66 690 01 Rev. C KohlerEngines.com 23 B B C C A A D E A Rich B Lean C Midpoint D Left Side E Right Side