avemachina
XSasperated but XScited!
Evening y'all! 1981 XS400 SH giving me trouble again.
I'll start with what's on my bike before I explain the symptoms:

Left-hand side, right-hand side. Spark plugs removed.
- UNI PK-92 pod filters direct to the carburetors, due to a massive tear in the H-hose (I know, I know, kinda set myself up for this)
- Carburetors rejetted one size up to 137.5 to compensate for pods.
- Carburetor needles at stock 3rd-groove position.
- Carburetor floats replaced with rubber type, tube-tested to have a static fuel level of 1mm below mating surface of the bowl for each carb. (23mm height)
- UNI UP-103 filter to the breather outlet.
- Gravity-fed fuel petcock; vacuum ports capped with fresh caps.
- Freshly replaced carburetor mounts.
- Carbs synchronized by manometer, freshly cleaned with new butterfly valves, oiled throttle cable with no snags.
- Autolite AP63 spark plugs gapped to 0.028".
- My little gear indicator has been removed; I'm back to a regular old neutral position sensor.
- Valve clearance set to 0.09mm inlet, 0.18mm exhaust.
. The bike runs decently, except I've been haunted by a hanging rev--even in 1st, it'll find its way up to 4000 RPM. After a little riding, the idle speed creeps up to 1500. Additionally, the neutral light seems to be a little dodgy.
As part of my testing, I ran it idle for maybe 10 minutes (3 turns out on 137.5). Nothing out of the ordinary, spark plugs were a golden color by the end, sat comfortably at 1200ish RPM.
I then rode for about 2 mi and noticed the rev issue coming back. This is also when I noticed the neutral light not always coming on. This has been happening occasionally since before the pods, when I had 142.5 main jets (what the bike had when I bought it; I set it to stock 135 for a time) and all-stock air intakes. By my reasoning, this means my idle circuit is okay, but maybe the main is still having issues? So I checked the spark plugs and I'm a little stumped--they aren't giving me anything obvious (no white, no real soot?)
Here's the left plug:


There's a little bit of what I can only describe as "caramelization" on the ground electrode and, alarmingly, little metal shavings. I assume (hope) these came from me being reckless screwing it in. The center electrode is starting to turn black.
And the right plug:

Right plug looks much cleaner, with light blackening on opposite sides of the center electrode and the neck of the ground electrode.
I'm not sure what this all means--is it even a carburetion problem? There's no smoke from the exhaust, and no popping on acceleration, just wild revs that fly up and want to stay up.
Any insight?
I'll start with what's on my bike before I explain the symptoms:


Left-hand side, right-hand side. Spark plugs removed.
- UNI PK-92 pod filters direct to the carburetors, due to a massive tear in the H-hose (I know, I know, kinda set myself up for this)
- Carburetors rejetted one size up to 137.5 to compensate for pods.
- Carburetor needles at stock 3rd-groove position.
- Carburetor floats replaced with rubber type, tube-tested to have a static fuel level of 1mm below mating surface of the bowl for each carb. (23mm height)
- UNI UP-103 filter to the breather outlet.
- Gravity-fed fuel petcock; vacuum ports capped with fresh caps.
- Freshly replaced carburetor mounts.
- Carbs synchronized by manometer, freshly cleaned with new butterfly valves, oiled throttle cable with no snags.
- Autolite AP63 spark plugs gapped to 0.028".
- My little gear indicator has been removed; I'm back to a regular old neutral position sensor.
- Valve clearance set to 0.09mm inlet, 0.18mm exhaust.
. The bike runs decently, except I've been haunted by a hanging rev--even in 1st, it'll find its way up to 4000 RPM. After a little riding, the idle speed creeps up to 1500. Additionally, the neutral light seems to be a little dodgy.
As part of my testing, I ran it idle for maybe 10 minutes (3 turns out on 137.5). Nothing out of the ordinary, spark plugs were a golden color by the end, sat comfortably at 1200ish RPM.
I then rode for about 2 mi and noticed the rev issue coming back. This is also when I noticed the neutral light not always coming on. This has been happening occasionally since before the pods, when I had 142.5 main jets (what the bike had when I bought it; I set it to stock 135 for a time) and all-stock air intakes. By my reasoning, this means my idle circuit is okay, but maybe the main is still having issues? So I checked the spark plugs and I'm a little stumped--they aren't giving me anything obvious (no white, no real soot?)
Here's the left plug:


There's a little bit of what I can only describe as "caramelization" on the ground electrode and, alarmingly, little metal shavings. I assume (hope) these came from me being reckless screwing it in. The center electrode is starting to turn black.
And the right plug:


Right plug looks much cleaner, with light blackening on opposite sides of the center electrode and the neck of the ground electrode.
I'm not sure what this all means--is it even a carburetion problem? There's no smoke from the exhaust, and no popping on acceleration, just wild revs that fly up and want to stay up.
Any insight?