Buell XB12S runs rough after spark plug change

[zaxrex]

OK... I checked the static timing this afternoon. I put the bike in 5th gear, pushed the bike forward until I heard the fuel pump activate and the CPS read from "0" to "5" and checked the timing hole. There was NO vertical line. The timing can't be that far off, can it?? Is it possible I have a faulty CPS?

[Iamarchangel]

If you didn't touch the timing previously, then don't bother looking there.

You've double-checked the plugs, so they're probably good. Nothing stands out in your narrative.

No codes means the computer isn't picking up a problem so look for issues that are not on sensors.

Plug wires:
1. one of mine was really worn. Somebody had previously left it twisted so it had worn against the frame mount. The rear spark was going to both cylinders. Replace and reroute did wonders.

2. Very difficult to be sure of solid wire to plug contact on the rear cylinder. It took several tries before I was sure. Actually bought the tool for next time, just because.

[zaxrex]

@ lamarchangel:
Thank you for your reply! Very good suggestions. I'm thinking about pulling the plug wires and checking the resistance as well as adding some dielectric grease on both contact points. I do want to check my timing because the old spark plugs were covered in black powder (running rich), so I'm guessing it's either the timing or the fact that the PO ran a Jardine pipe without a tune. I also had to futz around with the velocity stack to get my airbox off to access the front spark plug. I wonder if I should check the TB?

Thanks for the replies!

[zaxrex]

Well some potential bad news...

I fear that the engine may require a rebuild. After pulling my spark plugs a second time, I noticed oil around the plug boot. I also noticed that the aft cylinder spark plug hole had evidence of cross-threading at the top of the thread. I fear that some of that metal dropped into my combustion chamber and wedged between the cylinder sidewall and piston This morning when I started the bike (after sitting for 2 days), smoke was coming from the exhaust (during warmup) and after 20 seconds of rough idle, the motor conked. I restarted the motor and it idled rough, but OK and the smoke ceased. Looks like I'll be doing a compression test later today

[zaxrex]

Does anyone know what the nominal compression should be per cylinder (for the XB12s)?

Or I could calculate it if someone could provide me the compressed or TDC cylinder volume....

[Iamarchangel]

COMPRESSION TEST PROCEDURE
Combustion chamber leakage can result in unsatisfactory
engine performance. A compression test can help determine
the source of cylinder leakage. Use CYLINDER COMPRESSION
GAUGE (Part No. HD-33223-1).
A proper compression test should be performed with the
engine at normal operating temperature when possible. Proceed
as follows:
CAUTION
After completing the compression test(s), make sure that
the throttle plate is in the closed position before starting
engine. Engine will start at an extremely high RPM if
throttle plate is left open.
1. Disconnect spark plug wire. Clean around plug base and
remove plug.
2. Connect compression tester to cylinder.
3. With induction module throttle plate in wide open position,
crank engine continuously through 5-7 full compression
strokes.
4. Note gauge readings at the end of the first and last compression
strokes. Record test results.
5. Compression is normal if final readings are 120 psi
(827 kPa) or more.
6. Inject approximately 1/2 oz. (15 ml) of SAE 30 oil into cylinder
and repeat the compression test. Readings that are
considerably higher during the second test indicate worn
piston rings.

[zaxrex]

Thanks. I take it that came right from the service manual? DOH!

[Buzzerz]

When I first checked my timing it was almost out of the window. Set it right in the middle, runs like a different bike, better tick over, less spluttering etc

[zaxrex]

I forgot to give this thread a resolution! I have no idea why, but when I pulled my front plug to do the compression test, I found that the electrode was smashed and was only gapped to 0.008"! It must have been bent when I put the plug in the first time. I'm in disbelief that the bike ran as well as it did! I thought I changed out both spark plugs and checked the gap, but I guess I only did the rear . Anyhow, I regapped to 0.035" and the bike runs beautifully. Now it idles at 1000 rpm at TPS 5.3% and no longer misfires.

Buzzers: thanks for the info. I actually checked the timing again (this time with a bit more attention) and found that the timing mark on the flywheel was smack-dab in the middle.