Down to one cylinder at low rpm

Ok, I have a 2008ish (mag wheel) 1200 8V
Today whilst scooting along a lovely country road I came to a halt at an intersection and she dropped to one cylinder.
A bit of WTF? and farting around shows that the missing lung only happens below 2500rpm.
Back home for a bit of diagnosis.
Left lung is out at low rpm
Checked plugs, visible spark on both. (New plugs and NGK caps were fitted about 10k ago)
Swapped plugs side to side. left side still dead
Swapped coils side to side. Left side still dead.
Swapped injectors side to side. Left side still dead.
Pulled the valve covers and checked clearances, all good.
Compression test - both sides the same (145psi)

More on the symptoms. Higher rpm with very little throttle and shes sweet as on two lungs. Roll the throttle open below 2500rpm and shes on one cylinder until rpm gets above 2500 then shes off like a scalded cat.
Cracking the throttle open at any rpm above 3000 and all is well.

I’m assuming it’s been rollerised?

Yes - got the kit from you Pete - you might remember the saga of the slipped cam timing. [You must be registered and logged in to see this link.]
I rollerised it while doing that.

OK, let me cogitate for a bit and see if anyone else comes up with any smart ideas.

I'm going to pull the cover from the cam sprocket on the left side and check valve timing tomorrow. I'm not gonna do it now because I'm several beers deep at the moment

Cam timing is fine, pin has not come out through hole in oil flinger plate like last time.
Starting from cold this morning it ran and idled on both cylinders for about 30 seconds then started to lose the left cylinder.
Presumably the ecu delivers richer fuel mix at cold start - it seemed to like that.

An observation, but probably nothing to do with current woe's. Quite a lot of milky condensation on the inside of the tappet covers. This bike does not do short cold runs. Every trip is at least 50km.

The 8V’s run stupidly cool, the Mayo in the rocker covers is very common.

I’m leaning towards a spark issue. Weak spark would tend to fail at leaner AFR. You said you replaced caps and plugs. Did you do leads at the same time?

Replaced the plugs, caps but not leads, about 10k ago. Are the leads anything special?
Standard automotive HT lead be ok? (It currently has wire-core leads.)
I swapped coils and leads complete from side to side but the missfire stayed on the left.
I'll grab some new plugs today anyway.

Just standard copper core is fine, don’t use silicone lead, they’re a nightmare. It may not fix it of course but it’s best to look at the easy stuff first.

I've ordered new plugs as none of the automotive parts suppliers around here (or the motorcycle shop) have them.
I'll see if anyone has copper core plug wire and the crimp on terminals.
I'll run it in the dark tonight and see if I can spot any spark leaks.

You don’t need the fancy platinum ones. CR8EK-B’s work just fine.

Yes I've ordered the CR8EKB ones
I've just made up some new copper core leads which has made no difference.

It’s very unlikely to be ECU. Have you measured the air gap on the phase sensor? If it’s too wide and the phase sensor is getting a bit tired that can cause issues.

I have no idea what or where that is.
I'll see if I can find a manual.

Top left of the timing chest in front of the left cylinder.

Voltage regulator?

Alternator is internally regulated. Lights and dash will die before spark on one side.

Did you check the sparkplug of the left cilinder? Wet and/or dark? Or the opposite (white/grey)?

My bike (8V 2016) sometimes has the same, also left cilinder, but it's just a single miss and only at idle. Happened after I uploaded the Beetle map, might have been there before but never noticed. Bike runs great but when cold a little low on idle (1000 rpm), I feel I need to try to raise the CO setting (didn't do that yet).

jakepeewee wrote:

Did you check the sparkplug of the left cilinder? Wet and/or dark? Or the opposite (white/grey)?

My bike (8V 2016) sometimes has the same, also left cilinder, but it's just a single miss and only at idle. Happened after I uploaded the Beetle map, might have been there before but never noticed. Bike runs great but when cold a little low on idle (1000 rpm), I feel I need to try to raise the CO setting (didn't do that yet).

I have swapped everything external (coils, leads, caps, plugs, injectors) from left to right but the problem remains on the left.
New plugs should arrive today. New leads fitted yesterday.
I will also investigate Pete's suggestion today.

This bike has only done 12000km. I thought I had found a great deal when I purchased a brand new unused 2008 bike in 2018. It seems not.

Well I've been too busy for the last week to do anything with the bike. I installed the new plugs that finally arrived.
I went though every plug and connector that I could find under the tank and seat, and whadayaknow its back on 2 lungs.
Was it just a plug? Why would a plug fail at low revs but not at high?
The mysteries of the Guzziverse..
Who cares, it seems to be back to normal, and I'm relieved about that.

I had a plug that failed at 6000 RPM only.



Fuctifino.