Topic: What does this sound like? Rough engine, intermittent power loss

[speeed001]

Hello all, I'm hoping to get advice on some trouble. My 1975 CB550K engine is running rough, and I can't get a sense of whether it's fuel related, electrical related, or otherwise.

The engine is running very rough. The bike will start fine, maybe even run fine with full power and all for a while, but inevitably it will start sputtering accompanied by a loss of power.

I've recorded sound of it happening, with my iPhone in my jacket pocket as I pulled away from the curb, then came to an intersection with a stop sign. You can hear the problem best on acceleration: https://drive.google.com/file/d/0B6ilOEc_OcySY0dLOGtmcUl4SFU/view?usp=sharing

The power loss is so intermittent that it will come and go several times within just a few seconds. It feels almost electrical in nature, as if there is a loose wire somewhere that is causing one of the spark plugs or coils to fire inconsistently. There's a noticeable loss of power when it cuts out, and the power surges right back when it cuts back in.

The first time the bike started doing this, I thought it might be poor timing. I re-set the timing, set points gap, and checked gap for all spark plugs, and that seemed to help, but it just started up again a couple of weeks later.

I then thought it might be weak voltage to the coils, so I charged up the battery overnight and removed the coils, cleaned up the connections to frame/ground, and checked blue/yellow wires from points to coils. Still the same.

I also thought it might be fuel related, so I removed the tank, and checked for good flow from both petcock outlets. Check. Also, carbs were recently rebuilt with all new jets and valves.

I'm at a loss. Anyone have suggestions?

Thanks!!

Thanks!

[PeWe]

Intermittent ignition failures? Is it one cylinder that runs bad or is it 2?
If 2 running bad its usually 1,4 or 2,3 when they share same coil and point with condensor and the wiring between point and coil.
1 cylinder only, a bad ign wire? I have had one bad ignition wire, one carb could sneeze occasionally that became worse until I figured it out. Bike ran rough and sometimes horrible to drive on low rpms, 1500-3500 rpms.

[Tews19]

Sounds like some cylinders are not firing.

[speeed001]

Thanks, y'all. I couldn't figure out how to tell whether it was just one cylinder or two, or which ones it was. I wound up replacing coils, which seemed to produce better firing in general, but I still had the intermittence problem. While I had the points cover off, I noticed that one of the points was arcing noticeably more than the other, despite having set the gaps recently, and I read in another source that's an indicator of a failing capacitor. I replaced both capacitors with new, and I have ridden a few miles with no misses at all... so either new coils and caps solved the issue, or new capacitor, or some combination of the two.

[evanphi]

Thanks, y'all. I couldn't figure out how to tell whether it was just one cylinder or two, or which ones it was. I wound up replacing coils, which seemed to produce better firing in general, but I still had the intermittence problem. While I had the points cover off, I noticed that one of the points was arcing noticeably more than the other, despite having set the gaps recently, and I read in another source that's an indicator of a failing capacitor. I replaced both capacitors with new, and I have ridden a few miles with no misses at all... so either new coils and caps solved the issue, or new capacitor, or some combination of the two.

What brand were the old condensers? If Diiachi, it was probably them...