Engine: Engine Rpm's Too High

Depending on what equipment the engine is hooked up to, you may be able to control the RPMs with gears. If the RPMs are too high, try dropping it down a gear. This can solve the problem quickly and easily.

The springs of the carburetor are part of the linkage setup. These springs help control the functions of the carburetor under all operating conditions, and work together with the linkages. To check the configuration of these springs, you will have to refer to a repair manual for your make and model.

The carburetor mixes air and fuel together and feeds the mixture to the engine. If the engine RPMs are too high, the carburetor may be improperly adjusted. To re-adjust the carburetor, first locate both idle screws on the carburetor. One is marked L (low) and one is marked H (high). Turn both screws all the way in to shut off the fuel, then turn in the opposite direction for 2 turns. Next, start the engine, and let it idle for a few minutes to get it to operating temperature. Now, begin the adjustment by turning the L screw clockwise until the engine starts to slow, then turn it in the opposite direction until it once again starts to slow. You will want to set the screw at the midpoint of these two stopping points. Next, use a tachometer to gauge engine speed, and set the idle speed screw to bring the engine to 1750 RPM for aluminum-cylinder engine or 1200 RPM for an engine with a cast-iron cylinder sleeve. Then, at full throttle, turn the high speed or main jet screw clockwise until the engine begins to slow. Then, turn the screw in the opposite direction until the engine begins to slow. Once again, you will want to set the screw at the midpoint of these two points. Once adjusted, check the engine acceleration by moving the throttle from idle to fast. The engine should accelerate smoothly. If it does not, you will need to re-adjust the mixture screws.

The gasket below the carburetor prevents air from entering the intake under the vacuum, created by the engine. A leak in this gasket can cause a high idle. To check for a leak, you will have to remove the carburetor for a visual inspection. To begin this repair, remove the air cleaner assembly and filter. Then, remove the bolts securing the carburetor to the engine. Remember to pinch off the fuel line to prevent a spill. Remove any linkages at the carburetor then remove the carburetor itself. Check the condition of the gasket, looking for any signs of a leak. Gaskets are designed for one-time use so you will have to replace the gasket even if the old one looks good. This is because they can only be compressed once. With the gasket replaced, install the carburetor, and hook up the linkages. Secure it down with the bolts and reinstall the fuel line, and remember to un-pinch the fuel lines to allow the flow of fuel. Finally, re-install the air cleaner assembly and filter.

The linkages on the carburetor control the carburetor’s operation. Check to make sure all the linkages are attached and functioning properly, and that there is no debris caught in the linkages. To check the configuration of these springs, you will need to refer to the service manual for your engine type and carburetor.