A mechanic is inspecting the fuel primer system on a reciprocating engine used for cold-weather starting. Which statement correctly describes the function of this system?
- AIt circulates warm oil through the engine before start to reduce internal friction
- BIt delivers a metered charge of raw fuel directly into the cylinder intake ports or intake manifold, bypassing the carburetor, to aid starting
- CIt preheats the induction air before it enters the carburetor throat
- DIt automatically enriches the mixture during the first few minutes of engine warm-up
Show answer & explanationAnswer & explanation
Correct answer: B. It delivers a metered charge of raw fuel directly into the cylinder intake ports or intake manifold, bypassing the carburetor, to aid starting
The primer system uses a manually operated pump or electric solenoid to inject a small, metered quantity of raw fuel directly into the cylinder intake ports or manifold, bypassing the carburetor's normal metering, to provide a combustible mixture for starting, especially in cold weather when fuel vaporization from the carburetor is poor.
Why the other options are wrong
- A. Circulating warm oil describes an engine preheater or oil dilution-related preheating, not the primer.
- C. Preheating induction air is performed by carburetor heat or an induction air preheater, not the primer.
- D. Automatic mixture enrichment during warm-up is not the primer's function; it operates only during starting.
Fuel Primer System
A starting aid that delivers a metered charge of raw fuel directly to the cylinder intake ports or manifold, bypassing the carburetor, to assist cold-weather engine starts.
- Bypasses carburetor metering entirely
- Delivers fuel directly to cylinders/manifold
- Most useful in cold weather when vaporization is poor
Memory trick: Primer is a direct 'injection shot' of fuel straight to the cylinders, skipping the carb line.