For a combo mixture screw, the λ (lambda) vs. screw-opening curve looks different from a normal fuel screw, because it affects both air and fuel together.
This changes the graph shape.
Here is what happens:
This is why combo screws are sensitive near the first 1–2 turns.
This changes the graph shape.
Here is what happens:
1. Combo screw → mixture change is NOT linear
With a fuel screw:- Turning OUT = more fuel → steadily richer (λ goes down smoothly)
- First part of the travel: mostly changes airflow → λ may lean out
- Middle part: strongest fuel flow increase → λ drops (rich)
- End part: passage saturates → mixture stops changing much
2. Typical λ vs turns curve (for combo screw)
Expected behavior:
- 0–0.75 turns→ The passage is almost closed
- Small opening increases air more than fuel → leaner
- λ rises a bit
- 0.75–2 turns→ Main mixture zone
- Fuel starts increasing more than air
- λ drops → mixture richer
- 2–3.5 turns→ Curve flattens
- Passage near fully open → both air & fuel maxed
- λ stays stable
- Too many turns causes unstable idle
3. Summary of combo-screw curve
| Region | Screw Opening | Effect | Lambda Trend |
|---|---|---|---|
| A | 0–0.75 | Air increases faster than fuel | λ ↑ (lean) |
| B | 0.75–2.0 | Fuel increases faster | λ ↓ (rich) |
| C | 2–3.5 | Passage saturated | λ stabilizes |
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