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.

[malik]

My V7C had similar symptoms some years back. Flat spot just around 4,000rpm (motorway speed - annoying). Did all sorts to try to fix it, but in my case I found it was a flat spot in the TPS itself. I identified this by connecting up Guzzidiag and reading the TPS behavior when using the throttle. Much more obvious from the Guzzidiag readings. I replaced the TPS (from a spares Breva I just happened to have lying around - actually, intentionally bought for just this sort of thing).

Note that the local Guzzi mechanic solved a similar probem on a customer's  bike by LUBRICATING the TPS. if this works, it's a much cheaper fix.

If you're balancing the TBs you already have Guzzidiag - connect it up & explore what's in there - could be something else that the readings could highlight.

Good luck.

[sign216]

Here's some ideas on this, esp. for bikes of this era (first issue of the smallblock V7);

Inconsistent Running – Inconsistent loss of power while running.   Difficult to diagnose, but here are some suggestions.

a)   The flywheel sensor, right side of bell housing, below the throttle body, may pick up particles of clutch and other debris, interfering with its function.  Unscrew it and clean. 
b)   Fuel injector not fully seated.  Uncommon, but an injector may not be fully seated.  Inspect carefully and re-seat.
c)   Throttle Position Sensor (TPS) is going bad. 
d)   Sidestand is dropping slightly while running, activating the stand safety switch.

[sak]

Thanks for the suggestions! Update: I've done the following:
- Checked TPS for errors/flat spots with Guzzidiag, everything OK
- Reseated injectors and reconnected cables
- Checked crankshaft position sensor, it was clean

So after the above, still having the stumbling/erratic running issue above 4000 rpm. And it's actually doing it with the engine cold as well. The tach jumps around +-200 to 300 rpm when holding steady throttle at high rpm in neutral. When under load I can feel the bike surging.

Any other suggestions, I'm all ears!

[Vagrant]

Have you checked for air leaks.

[sak]

Yes, no air leaks around the throttle body connections.

[guzzisteve]

You could ask Beetle for a different map in case yours got corrupted on install, even pay him for one a bit richer on big end.

[Michael_A]

Tach jumping around is one of the indicators of a coil going bad.... sometimes the only indicator aside from poor running.

[malik]

Tach jumping around is one of the indicators of a coil going bad.... sometimes the only indicator aside from poor running.
[/quote

Also an indicator that the junction box for the yellow wires from the alternator to the reg/rec is failing or not connecting properly. This white nylon junction  on the V7C lives under the front of the tank just near the tank puck on the RHS - or at least that's where it was when new. A known & not uncommon phenomenon on the V7 Classic. Have not heard it happening on the 1TB V7s or the Breva/Nevada. Check the connector for scorch marks or burnt wires, or just replace the connector with something better.

It doesn't SOUND like this would result in your symptoms but with electrickery, you never know your luck in a big city.

I would also test the spread of fuel coming out of each injector. I use a paper towel or toilet paper to catch the atomised drops. Or just use a PEA-based injector cleaner anyway. I would do this before taking the fuel pump out of the tank & checking the state of the filter sock, the hoses & replacing the filter. I've seen that sock crammed full of debris before & they are easily & cheaply available. Ensure it's not a fuel problem first. Apparently, the original fuel filter itself is rated for only 30,000km.

 BTW, my V7C did not like Shell 98 (a premium fuel here in Oz) - unexplained failure to proceed. It's a heron head, designed for poor fuels, not premium ones engineered for high performance engines. 91 & 95 I've had no trouble with as long as the fuel is uncontaminated. A cap full of metho in the tank should help dilute & burn any water in the fuel tank that has managed to find its way in there.

Good luck, keep on keeping on,

[malik]

After fuel, the next is spark. You said you had shredded rubbers on the spark plugs. I would replace the plug caps anyway - they are super cheap for the V7C, while there I would ensure that there is no corrosion on the HT wires' copper - I snip the ends off to ensure a clean contact. Then test the resistance with your meter - should be about 8, I think with the cap on.

[DenverSteve]

I guess I have less time on my hands than many here. I would ride it to my dealership/mechanic and leave it for a proper diagnosis and repair.