How does a cracked or leaking rubber intake manifold (carburetor insulator) affect the operation of a motorcycle engine?

1. It draws unmetered air into the cylinder, causing the engine to run lean, idle erratically, and hang or surge in RPM.
2. It causes fuel to leak out of the intake manifold onto the crankcase, creating a rich mixture.
3. It restricts the air flow into the carburetor, acting as a choke and lowering idle speed.
4. It causes the exhaust system to clog with carbon, leading to high backpressure.