How can tighter valve lash than specified affect an EFI engine?

Tighter valve lash than specified can have a significant impact on the performance of an Electronic Fuel Injection (EFI) engine, specifically leading to rich running and a loss of power. When the valve lash is set too tight, the valves may not close fully or may not have sufficient time to seat properly. This can lead to incomplete combustion of the air-fuel mixture because the exhaust valves may not open at the correct time or may stay open too late, allowing exhaust gases to impede the fresh intake charge during the next cycle.

As a consequence, the engine can begin to run "rich," meaning there's too much fuel in comparison to the amount of air available for combustion. This imbalance can cause several issues including a decrease in engine power, as the engine is unable to operate efficiently when the air-fuel mixture is not optimal. Additionally, richer mixtures can result in increased fuel consumption and can also lead to carbon fouling of spark plugs, further impacting performance.

Understanding these effects underlines the importance of maintaining proper valve lash settings in an EFI engine to ensure efficient combustion and optimal engine performance.