TOPIC:

Howdy all,
I've spent the last few weeks troubleshooting some issues with my 1980 KZ550. Aside from usual maintenance the last few years, the bike has performed fine. I've read through similar posts trying to diagnose my problems, and hope to get some opinions.

About a month ago, during some local riding, about half power cuts out and I get a throaty exhaust sound. I stop for a while, assuming some things aren't firing. I pull and clean plugs, reattach, and the bike is fine to get home.

Weeks ago, around 30 minutes into a highway ride, the problem is back. Checking plugs and wires again, plugs 2 & 3 are wet, while 1 & 4 are cloudy white. I start up, and the throaty exhaust is still going. I let the bike cool for a bit, making some calls to try and get some opinions. I was pressed for time, getting to a job, so I tried one more start, and surprisingly she sounded and ran just fine to get me to my destination. When I had it back at home I replaced plugs, and went through cleaning and lightly sanding contacts to make sure energy flow was consistent.

The bike ran fine for another week, until it didn't. I started at the plug wires, and noticed they were fairly loose/worn at the plug caps, possibly from all the recent plug checking. I cut them down slightly, for a cleaner contact to the caps. No change.

Ultimately, I purchased a new pair of the green Dyna coils. Upon startup, I had a bit of white/gray exhaust smoke that dissipated after some neighborhood riding. The coils have performed well for a few days, unfortunately, the exact same power loss and throaty sound is back.

Am I to assume that it is now the electric ignition I should be checking?

Thanks for assistance.

If not already done, would assure that the valve clearances are within specs.

Good Fortune!

did you get new wires?

DSummerlin, I did get new wires with the coils.

Patton, currently pulling the valve cover. The smaller top covers for the hose are filled with dried oil/dirt..

Ignition feed to one coil and/or carb problem 2 and 3 I reckon.

lightly sanding contact breakers not recomended, if pitted replace contact breaker points and capacitor. Maybe you have defective contact breaker points firing 2/3 hence plugs are wet....but also a lean condition on 1 and 4.

Replace points and condenser, or better upgrade to electronic igniton...clean carbs and check fuel levels then look a valve clearances in that order is what I'd do.

I like really like the 550's,keep at it, they are well worth doing...

The bike does have electric ignition. I'm checking the valve clearance and cover.

I would like to get the carbs cleaned and rebuilt. I'm not happy with the last cheap rebuild kit I purchased. There are some leaks at the seals, and the tune of the bike had changed. Another rebuild may be coming.

Patton,
Clearance seems to check out.
1: .18mm
2: .15
3: .18
4: .18
5: .1
6: .13
7: .15
8: .1

As I said, the top covers for the vacuum hose had quite the buildup of dried gunk. The hose itself had some buildup as well, so I've cleaned the around the valves, and putting a new hose on.

GatlinM wrote: ... about half power cuts out and I get a throaty exhaust sound. I stop for a while, assuming some things aren't firing. I pull and clean plugs, reattach, and the bike is fine to get home.

Weeks ago, around 30 minutes into a highway ride, the problem is back. Checking plugs and wires again, plugs 2 & 3 are wet, while 1 & 4 are cloudy white. I start up, and the throaty exhaust is still going. I let the bike cool for a bit, making some calls to try and get some opinions. I was pressed for time, getting to a job, so I tried one more start, and surprisingly she sounded and ran just fine to get me to my destination. When I had it back at home I replaced plugs, and went through cleaning and lightly sanding contacts to make sure energy flow was consistent.

The bike ran fine for another week, until it didn't...
exact same power loss and throaty sound is back.

Am I to assume that it is now the electric ignition I should be checking?....

If not already done, would perform the clear tube test on each carb to assure that the fuel level is within specs.

A too high fuel level may result in excessive richness that eventually douses or partially douses the plug spark and causes a throaty burbling exhaust sound produced from the over-rich cylinder.

Other possible causes for over-richness include dirty air filter(s), or a blocked stock air filter (eg., pair of gloves, shop rag, etc. stored underneath the seat). And possibility of a loose main jet.

A weak battery can also result in weak spark.

Good Fortune!

Thanks, I'm going to start checking the carbs more in depth, soon.

I had it back together after cleaning up, and checking valves. Started it to check if there was any difference, just plenty of loud backfires.

GatlinM wrote: Thanks, I'm going to start checking the carbs more in depth, soon.

I had it back together after cleaning up, and checking valves. Started it to check if there was any difference, just plenty of loud backfires.

Are backfires through the carbs or out then exhaust?

Good Fortune!

If not already done, would perform the clear tube test on each carb to assure that the fuel level is within specs.

Yes, new coils and leads with original electronic ignition, unless your IC ignitor box is on the way out - unlikely, more sounding like a carb or fuel supply problem.

This seems an intermittent rather than continuous problem, letting it cool then it starts again, sometimes a blocked fuel filter or fuel tank strainer can do that.

One quick easy test might be drain the carbs, spray some easy start / carb cleaner into the airbox or onto filters and then fire it up for a few seconds. Don't make a habit of this as it washes oil off the bores, but If your backfiring problem persists then I'd look more towards ignition timing, wiring , block connectors and coil connections,

Backfire is from the exhaust. It seems to hit harder when I give more throttle.

Tube test checked out ok. Fuel filled level with the bowls. Fuel draining from carbs is clear.

I do get a bit of fuel splashing back into the air filter/box, though checking today it isn't any different than when I've seen it months before. Filter is relatively dry.

I have also been getting rougher knocking sounds over the last few months. That tend to clear up after the engine's warm. I feel they are coming from the front valves. Yesterday's clearance check seemed to confirm they were close to specs, though.