# Road test log — real-world tune results

Empirical outcomes from actually flashing and riding, kept separate from the
static reverse-engineering docs (`TABLES.md`, `DEVICES.md`) since this is
field data, not derived facts about the ROM format.

## 2026-09-15 — `20262-arrow-delete-lowthrottle-composed.hex`, first real ride

Flashed after several days running plain stock `20262Map.hex` (SAI/O2 flags
still enabled despite SAI being physically removed, snorkel already removed
with zero main-table correction). Result: **major, immediate improvement.**

- **Stalling at lights / low-speed choking: fully resolved.** Not just
  fixed — noticeably *better* than expected: "a lot more low rev and slow
  speed control," easier to get going, smooth at slow speeds. Attributed to
  the Low-throttle fuel table correction (under ~10% throttle, both
  cylinders, +7% to +24%) plus the two corrected Idle Fuel Trim (CO) points.
- **Decel backfire (3-4.5k RPM, 2nd-4th gear): dramatically better, not
  eliminated.** Before: "backfires like crazy," reliably reproducible.
  After: 1-3 noticeable pops on a 5k→3k decel sweep in 2nd-3rd gear, and
  *not* reliably reproducible anymore (sometimes it doesn't happen at all).
- **New/newly-noticeable, minor**: holding steady revs at 5k, the engine
  can "break up and get a tiny bit throaty." Described as minor, not
  concerning, bike is very rideable as-is.

**User's own assessment**: "In the current state I could drive it as is and
be happy" — this is a real, working baseline, not a stopgap.

## Diagnosing the residual decel pop — reasoning, 2026-09-15/16

Two mechanisms were on the table for residual exhaust-side popping on
deceleration:

1. **Rich unburned mixture reaching the hot exhaust with no SAI assist to
   burn it cleanly** — the classic mechanism for popping *from the exhaust*
   on decel (as opposed to backfiring through the intake, which is the
   lean-misfire pattern). SAI's actual job was adding oxygen downstream to
   assist combustion of that charge; a fuel table can't replicate an air
   *supply* by adjusting how much fuel goes in. **This is the mechanism the
   user's own reasoning correctly pointed at** (session correction:
   "I mean it's still rich, since that's what caused the popping" — right
   call, corrected an overly-lean-leaning framing from earlier in the same
   conversation).
2. Unaddressed leanness in areas the current composed file doesn't touch.

**Important structural correction, made mid-session**: the Idle Fuel Trim
(CO) table (`0x53690`-`0x536AF`, 32 RPM-indexed points, same RPM axis as
the main tables — see `TABLES.md`) was initially assumed to apply only at a
literal stop. That's likely wrong. The table has real entries all the way
out to 10,000 RPM — no reason for that range to exist if it only ever
applied near idle. **More likely: this curve applies whenever the throttle
is closed/near-closed, at whatever RPM the engine happens to be at** — i.e.
it's the relevant table during an active decel sweep through elevated RPM,
not just idle-at-a-stop.

Given that, the composed file's coverage of this curve matters directly for
the decel-popping symptom:

| Curve region | RPM range | Correction status |
|---|---|---|
| Point 12 | 2400 | **Corrected** (see `compose_arrow_delete.py`) |
| Points 13-26 | 2600-6500 | **Untouched** — still Arrow's original values |
| Point 27 | 7000 | **Corrected** |

The user's actual decel sweep (5000→3000 RPM) runs almost entirely through
the **untouched middle section** of this curve. That's a more precise,
evidence-grounded candidate for the residual pop than either "lean the
idle" (don't — that's the low-throttle fix that's working great, protect
it) or "richen the higher range" broadly (that's a different symptom,
different table — see below).

**Two symptoms, two different tables — don't conflate them:**

| Symptom | Condition | Likely table |
|---|---|---|
| Decel pop | closed throttle, elevated RPM (falling through 3-5k) | Idle Fuel Trim (CO) curve, untouched middle points |
| "Breaks up/throaty" at held 5k revs | open throttle, sustained load | Main VE fuel tables — still 100% stock-Arrow, unaddressed |

The second one is the known, previously-flagged gap (no main-table
correction exists for the snorkel/baffle removal). It is a *separate*
project from the decel-pop investigation, not the same fix.

## Baffle removal considered and rejected as a fix for decel pop (2026-09-16)

User proposed removing the airbox internal baffle (on top of already-removed
snorkel), reasoning more airflow would "even out" the remaining popping.
**Rejected, reasoning below** — not because baffle removal is bad in
general, but because it's the wrong tool for this specific symptom:

- Decel popping happens at **closed throttle**, where the throttle plate
  itself (not the airbox) is the dominant restriction. Baffle removal
  doesn't meaningfully change airflow in that condition.
- Baffle removal *does* increase airflow at every **open**-throttle
  condition — exactly the untouched main VE tables. This widens the
  existing, already-flagged leanness gap rather than closing it, and is
  likely to make the "breaks up/throaty at 5k" symptom *worse*, not better.
- Per `COMMUNITY_TUNING.md`'s TTP dyno data, baffle-removal+2-1 already
  lands close to *full* airbox removal in airflow/power terms. Pulling the
  baffle on top of an already-removed snorkel pushes past what either
  reference data point in this project actually characterizes.

**Recommendation given**: don't pursue baffle removal as a decel-pop fix.
If pursued later for its own sake (more performance), it should come
*with* main-table correction work, not before it.

## Where this leaves things, if picked up again

Current file (`derived/20262-arrow-delete-lowthrottle-composed.hex`) is a
good, real, working baseline — user is happy running it as-is. If further
work is wanted:

1. **For the decel pop specifically**: pull real reference deltas for the
   untouched CO-trim points in the 2600-6500 RPM range (same source
   methodology as the rest of this project — `20184dynoTuneSteveO2-Disable.hex`
   vs `20186Map.hex`), test in isolation, don't touch the low-throttle
   fix that's already working.
2. **For the main-table gap**: the bigger, separately-tracked project —
   full VE-table composition for the snorkel/airbox-baffle removal, still
   not started (`COMMUNITY_TUNING.md`'s "~1340-byte main VE overlap").
3. Neither is urgent — current state is rideable and the user is satisfied
   with it. This is optimization, not a fix for something broken.