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uhryniuk f830f8937d Log real-world road test results and correct/extend the CO-trim theory

New research/ROAD_TEST_LOG.md: the 2026-09-15 flash of
20262-arrow-delete-lowthrottle-composed.hex was a major real-world
success (stalling fully resolved, decel backfire much reduced but not
eliminated). Captures the live diagnostic reasoning that followed:
correcting an overly-lean-leaning framing mid-session (residual decel pop
is more likely a rich-unburned-mixture-with-no-SAI-assist problem, not a
lean one), a structural hypothesis that the Idle Fuel Trim (CO) curve
likely applies whenever the throttle is closed at any RPM rather than
only at a literal stop (only 2 of its 32 points are currently corrected,
and the untouched middle range lines up with the residual pop's RPM
window), and the reasoning for rejecting airbox-baffle removal as a fix
for decel popping specifically (wrong mechanism -- closed throttle isn't
airbox-limited -- and risks worsening the separately-flagged, still
unaddressed main-VE-table leanness gap).

Also updates TABLES.md with the CO-trim applicability open question, and
brings TUNING_GUIDE.md's "local research assets" section up to date (it
still said maps were gitignored/unflashable, both stale).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FP2GaxS9HkUdL5sLBnjKje

2026-09-16 09:07:35 -05:00

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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:

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).
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:

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.
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").
Neither is urgent — current state is rideable and the user is satisfied with it. This is optimization, not a fix for something broken.

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