🔍 Key Concepts

• Effective stroke of the plunger in a helix‑type fuel injection pump (from port closure to end of upward stroke) • Relationship between the helix edge, the vertical groove, and the spill port in determining fuel quantity • How rotating the plunger with the control rack and gear changes from maximum to minimum (zero) fuel delivery

💭 Think About

• Look at where the spill port in the barrel is, and where the helix and vertical groove on the plunger are at the top of the stroke. Does the port stay closed for a long distance, or is it opened almost immediately? • Compare the shown plunger position with the two extremes you know: one where the helix keeps the port closed almost until the very end of the stroke, and one where the helix opens the port right at the start of the stroke. • Ask yourself: in this illustrated position, is the effective stroke long, medium, very short, or essentially zero?

✅ Before You Answer

• Identify clearly which way the plunger is moving during the delivery stroke (upward) and when the spill port first becomes covered. • Verify whether the vertical groove connects the helix edge to the spill port early or late in the stroke. • Decide whether the effective stroke length you see corresponds to maximum, normal, light, or zero fuel based on how much of the upward travel occurs with the port fully closed.