77 KZ650, No Spark

I have a 1977 KZ650 that doesn't have any spark. Several months ago I rode the bike and realized it was running on three cylinders. I checked the spark and it was VERY strong, so then I pulled the plug and realized it wasn't getting any fuel. Fast forward several months, I pull the carbs and clean them up. When I go to start it up with the nice fresh carbs, I discover the spark is now very weak.

I lightly filed the points as they were somewhat dirty, then I see no spark whatsoever. I then checked the points, clearance was a little tight, so I set them to .018". The coils are getting power to them from the ignition. The voltage on the points is 1 volt less than the battery. But twice when I am manually opening and closing the points while watching one of the relevant plugs, the other one fires while the one I'm watching does not spark at all.

What could be the problem here? What should I check?
And why would it go from strong spark to almost nothing in a few months? (I never messed with this at all)

Hi pipeburn, Check the sparkplug wires with an Ohmeter, and see what the required Ohms are per the manual. You can also trim 1/8 to 1/4 of an inch off the resistor cap end and re-screw them back on and retest for spark. A good cleaning of all the connections may be in order for these vintage bikes.I took a day and done all of mine on my KZ 650 E. Bob

You may have installed the advance rotor 180 degrees out of phase, or you have the plug wires/coil connections reversed. Double check - 1 and 4 on one coil, 2 and 3 on the other.

Good luck.

Pipeburn wrote: I have a 1977 KZ650 that doesn't have any spark. Several months ago I rode the bike and realized it was running on three cylinders. I checked the spark and it was VERY strong, so then I pulled the plug and realized it wasn't getting any fuel. Fast forward several months, I pull the carbs and clean them up. When I go to start it up with the nice fresh carbs, I discover the spark is now very weak...What could be the problem here? What should I check?
And why would it go from strong spark to almost nothing in a few months? (I never messed with this at all)

Hello, Pipeburn, and WELCOME to Z1r!

Is bike exposed to the elements while parked?

Good Fortune!

I noticed that the starter was also spinning slowly, even though the battery has a healthy 12.6 volts. I cleaned the connections at both ends of the ground strap, it seemed to help a little. The starte spins slightly faster, but it's still slow. I have a very faint spark now as well. I guess I just need to keep cleaning connections until it works again.

TeK9iNe wrote: You may have installed the advance rotor 180 degrees out of phase, or you have the plug wires/coil connections reversed. Double check - 1 and 4 on one coil, 2 and 3 on the other.

Good luck.

I never had any of this apart and it ran before, so I'm sure all this is fine. All I did was set the gap on the points.

tinlizzie37 wrote: Hi pipeburn, Check the sparkplug wires with an Ohmeter, and see what the required Ohms are per the manual. You can also trim 1/8 to 1/4 of an inch off the resistor cap end and re-screw them back on and retest for spark. A good cleaning of all the connections may be in order for these vintage bikes.I took a day and done all of mine on my KZ 650 E. Bob

I would check the resistance, but I don't have a manual to know what the spec is.

Patton wrote: Hello, Pipeburn, and WELCOME to Z1r!

Is bike exposed to the elements while parked?

Good Fortune!

It has been outside, though I will try to keep it inside now that it has nice shiny painted parts on it.

Pipeburn wrote: ...All I did was set the gap on the points.

If not already done, it's usually necessary to clean the contacts after setting the gap to remove any residue left from the thickness gauge.

Good Fortune!

A business card will work as a thickness gauge if you're out on the road and the points close up in an emergency. Another card treated with Acetone or MEK will degrease the ignition points.

Try not to get the MEK on your hands as it will remove the skin oils and be absorbed into the blood affecting the liver & kidneys. Avoid inhaling the fumes too as it is almost as bad on the lungs.

Check your battery voltage both before operating the starter and during and see the difference. I would charge it up first. Also check the voltage at the ignition coils, and compare. Probably got a bad battery or are loosing the voltage along the system. Make sure both of the battery cables have good clean connections, both at the battery and starter/ engine-frame.

I checked the resistance of the coils today. My ohmmeter has several different ranges (200k, 2000k, 200, 200, etc..) I had it on 200. One coil had 5.1 ohms resistance, the other 5.6 ohms. I think these should be okay.

I also tried jumping the coils to see if my problem lay in my wiring. I ran one jumper wire directly from the positive side of the battery to the wire on the coil that gets hot with the ignition. I ran another jumper from the wire that the points plug into and tapped it on the battery. The plug was laying on the head and never sparked.


Edit: I just realized that bypassing all that other stuff meant no condenser, and perhaps that's why there was no spark then. I'm going to see if I can test the condenser.

My understanding of the condenser/capacitor is it absorbs the current so the ignition points don't burn when they open and close. Yours may have failed. Did you try putting a screwdriver between the points for a short time to see if a spark was generated?

Spark failure can sometimes be caused by bad sparkplug caps(they should test out at 5K ohms),cracked sparkplugs wires(or for those Brits and Canadians, High Tension Leads)or ignition coils that have overheated.

If you have input voltage to the primary(small wires) side of the coils, and nothing going out, disconnect the related wiring to the coils and put an ohmmeter on both primary and secondary side of the coils. A hair dryer on high will heat up the coils simulating a hot environment without needing the engine to be running.

I only tested one spark plug cap, but it checked out perfect.

I googled how to check condensers and tried several methods. The simplest thing I saw was that if the points spark while opening, and mine do, that means the condenser is bad. The other simple test was to charge them, the see if there is a spark as you touch the wire to the case, I had no spark here either. I then checked to see if either one was shorted internally, and neither one was. I then "filled them" so to speak, and tested that. I was charging them with a battery that had 12.6 volts, but they only show 5 volts on a digital muti-meter, and barely moves the needle with an analog meter. And of course they drop off quickly as it discharges. So I'm thinking that while my condensers are not shorted, they have lost capacitance; They don't hold 12 volts, and they don't prevent arcing at the points, which is the purpose of the condenser.

It looks like I can get a new condenser for $9, I guess I should do that. I may do some more checking first, because I absolutely HATE buying parts I don't need.