Welcome Guest. Sign in or Signup

5 Answers

Question on priming the engine

Asked by: 803 views Aircraft Systems, Commercial Pilot, Flight Instructor, General Aviation, Private Pilot, Student Pilot

When we prime the engine by turning on fuel pump, pushing mixture full forward for few seconds and out, is the fuel being injected into the combustion chamber?



Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

5 Answers

  1. Kris Kortokrax on Oct 14, 2016

    It doesn’t matter whether you use the procedure you described for an injected engine or you pull out the plunger and push it back in on a carbureted engine, the purpose of priming is to inject raw fuel into the cylinder.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes

  2. Best Answer

    Bill Zaleski on Oct 15, 2016


    Just to be clear. You are never directly injecting the prime into cylinder. You are introducing raw fuel into the intake port, on the stem side of the intake valve. The fuel/air mixture must still enter the cylinder only when the intake valve is open during the intake stroke. This is true of either fuel injected or carburetor type engines.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes

  3. connor on Oct 16, 2016

    Before the engine start, not all intake valves are closed, aren’t they?

    0 Votes Thumb up 0 Votes Thumb down 0 Votes

  4. Bill Zaleski on Oct 16, 2016

    They are never all closed at the same time.

    -1 Votes Thumb up 0 Votes Thumb down 1 Votes

  5. connor on Oct 18, 2016

    Yes, the prime is introduced to stem side and some cylinders might have intake port opened before start. right?

    So the prime may slide into the cylinder just a little bit ?

    0 Votes Thumb up 0 Votes Thumb down 0 Votes

The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.