Took my bike in to have the rear tyre replaced. So I'm driving away after the tyre replacement, maybe about 5-6km, when all of a sudden on the N1, I start losing revs.
But not like, time to switch to reserve, but more like completely erratic revs. Open the throttle hard and the bike tries to climb, but keeps dropping the revs, to the point where I had to pull over. Drove home the rest of the way like that.
At low rev's the bike seems fine (as in under 4000 rpm). As soon as I exceed that, it seems the electrics get all messed up. If I have my indicator on, then the indicator stays on, but flashes off everytime I lose revs - making me think the problem is electrical - maybe the spark plugs arent getting power either.
Any ideas as to what could be wrong? I checked the fuses under the passanger seat. All seem fine. I'm about to start taking her apart now to check the battery connections, looms and any other connections I can find.

I havent replaced the rectifyer since I bought her from her previous owner, but I've never had electric issues before. She's always started first time etc.

Help

I don't know much about the V4 but I'd check the voltages on the battery, while off and with engine running. When you push the starter does it turn over as fast as normal or does it seem to struggle?

as I mentioned before, it has no problem starting - touch wood - and under 400rpm, the bike seems completely normal.

I've taken of the seat cowl, and everything seems normal. All the fuses are good. No visible loose connections. The loom is wrapped up good and tight in insulation tape... so.

I'll have to check the voltages and things, but as she stands, she looks fine.

loose earths then..check them all

Took it for a quick drive around the block, trying to rev it a bit to get the issue going (at first it drove fine for a bit), then it started messing up again.

Parked it and revved it, and i couldnt get passed 4000rpm at all. Switched OFF my headlights, and the bike just died immediately.

All lights were off (oil, neutral etc), bike did nothing at all when I hit the starter - was as if the batter wasn't even connected. Then after about a min or so, the neutral and oil light suddenly came on, and when I tried to start her, she started perfectly again!!???

Check all the wiring around the headstock, may be a damaged earth, check the speedo connector too as it may be jumping in and out of limp home mode.

HTH

Just to update :

I've disconnected the battery, cleaned the terminals, reconnected. No difference.
I unplugged the computer box (At least I think thats what the black box by my rear lights are), and reconnected. No difference.
Checked out the reg/rec, no burnt wires / brown plastic near the plug.
Checked the voltage at the battery terminals with the bike off - about 12.8v
Checked the voltage at the battery terminals with the bike on at 5000RPM - about 14.4v

Both seem to be correct voltages and as far as I can tell, my reg/rec is fine ?

I'l start taking the front cowling off tonight and check all connections there. I want to change the headlight bulbs anyway to something nicer anyway...

Problem solved. For completeness :

Turns out when I disconnected the battery, I never checked the other end of the cable where the negative (earth) connects to the chassis. It seems the previous owner had replaced this wire with a solid copper wire which had broken inside the electrical tape at the chassis end.

Once I replaced the wire, the bike runs like her old self again.