V7 Classic Stumble When Warm at High RPM

[sak]

Hi Everyone,

Recently picked up a 2010 V7 Classic which has an issue that's driving me nuts. The bike has done 40k km, with a regular service history. Here's the problem:
Once the bike is warmed up, it starts to stumble (misfire) when revving above about 3000 rpm, both under load and in neutral. Also, when revving around 4000-5000 rpm, the top end sounds like shaking a bag of marbles - a worrisome higher-pitched non-rhythmic noise. Originally it sounded like it was coming from the right cylinder, but after balancing the throttle bodies, it seems like it's now coming from the left cylinder. This may or may not be related to the misfiring, I've read that it could be the headers resonating or some such.

The bike idles and cruises fine at lower RPM and when the engine in cold. The bike also has a baffled aftermarket exhaust which is a bit less restricted than stock.

Here's what I've done so far:
- Valve clearances - rocker arms had some lateral play, not sure how much is normal
- Throttle body balancing
- Beetlemap ECU with TPS reset and relearn with GuzziDiag
- Checked air filter, was changed 7000 km/4000 miles ago and looks OK.
- Checked for vacuum leaks around throttle body
- New header gaskets
- Compression test: 130 PSI right cylinder, 140 PSI left cylinder. Readings were the same after adding a bit of oil to the cylinders. Definitely seems low, but my gauge might not be calibrated.
- Spark plug caps have been changed to NGK by previous owner. The rubbers where the plug wire meets the ignition coil are pretty much shredded, could this cause issues?

Both header pipes are blued all the way to the exhaust, so it seems like this bike has been running super lean.

Any ideas are appreciated!

[sign216]

SAK,
How do the plugs look?  Can you attach a picture of them?
It might be lean, esp. w the aftermarket exhaust. 
Could also be a spark issue, like the spark is "leaking out" through the shredded wire insulation.

I've got an '90 V7 Classic, myself. 
I've got to give this some thought.
Joe

[MikeP996]

Was it doing the misfire thing BEFORE you did any of the work you mentioned or was the work done in an attempt to correct/diagnose the problem?

[guzzisteve]

Try taking apart plugs to the ECU & coils to clean w/contact cleaner or DeOxit, looks like you checked most.

[sak]

Thanks for the responses!

I haven’t dont a proper plug chop, but the plugs in general look decent with white tips. Not quite as lean looking as before throttle body balancing and the Beetlemap.

I did the aforementioned activities because of the misfire, and also because the idle was erratic and would sometimes shut off (engine cold and warm). Now the idle is good, but the misfire is still there.

[Michael_A]

Could be a coil getting ready to take a dump (and/or the plug leads also). Don't know if MG has resistance specs (maybe those more knowledgeable can venture some, or a ballpark), but a quick check with an ohm meter could at least indicate if it's shorted or high resistance. Sometimes one going bad starts to break down when they get hot, or under various vibration frequencies.
Did stumble across some approximate resistance specs: Primary should be around 3.5 to 5 ohms; Secondary somewhere around 9K to 15K ohms. A dead open or dead short (zero resistance) = immediately bad, though it MAY still sort of work... but will miss or quit.