You must replace the intake gasket when air begins flowing to the cylinder heads.
The intake gasket on a Harley-Davidson motorcycle keeps air from entering the motorcycle’s cylinders. It is located between the intake manifold and the cylinder heads. The gasket requires replacement once the motorcycle backfires or if the motorcycle doesn’t sound like the motor is working properly. This procedure requires some knowledge of the inner workings of a Harley-Davidson. You must also remove the air cleaner cover and backplate before removing and replacing the intake gasket.
1. Disconnect the carburetor from the manifold. To do this, turn the fuel system to “Off” with your hand. Once you stop the fuel supply, disconnect the fuel line from the carburetor. Detach the fuel enrichener knob from the bracket — located above the horn. Also disconnect the throttle and idle cables from the carburetor — unscrewing them by hand. Pull the vacuum hose away from the carburetor thus releasing the carburetor from the manifold and seal ring.
2. Remove the manifold from the cylinder head. Do this by removing the 10 screws that hold the manifold in place with a standard screwdriver and the manifold flange from the two connectors on the manifold. Detach the Manifold Absolute Pressure (MAP) sensor connector from the wiring harness.
3. Replace the intake gasket — located between the manifold and cylinder heads. Once you place the gasket in place, seal it with the manifold flanges and manifold. Ensure you tighten the 10 screws that hold the manifold in place by hand. Reinstall the seal ring on the portion of the manifold that connects to the carburetor.
4. Reinstall all parts removed from the carburetor including the throttle and idle cables, air cleaner backplate and the MAP sensor connector. Also, tighten the manifold screws to 8 to 12 foot-pounds with a torque wrench. Reinstall the air cleaner filter and cover as well as the enrichener.