KZ400 has weak/sporatic spark!...

So after a $211 bill at the bike shop my bike was running like never before. It fired first kick from dead cold, and held a perfect idle. I couldn't have been happier...then I went to go start it yesterday and got a huge load of disappointment....

I kicked her off and she fired right up...then died. A few more kicks and no luck so I gave full throttle (clear flood) and she fired but was running on one cylinder or both very poorly. It would barely hit 2k RPM at full trottle. I pulled the plugs and found soaked, cleaned and tried again. Now I have no spark whatsoever. All of the wiring is intact and unobstructed, but still no spark.

I'm completely stuck. I've considered a new coil, but my bike budget has been cut-off until my savings recovers from some unexpected bills and I just finished the endorsement test and I'm ready to ride...

If I can't figure this out for next to no cash It may be next f-ing summer before I get to ride her. I've working on this bike since last august to have it ready...I'm going crazy...

Please help me.:dry:

That's bad luck.
Well, what did the bike shop do for $211?
If I understand correctly when you have a plug in the spark plug cap and the plug is grounded to the engine, you have no spark. Correct?
Do you have lights, does everything else electrical work?
Check the battery.
Check fuses.
Check the voltage to the coils.
Check coils.
Check wires.
Check caps.
Check plugs.
Hopefully it will be something simple since "yesterday it worked, today it doesn't".

I have full electrical power, and all of the wires are accounted for and in place, all fuses are good, it's got a new battery (and was hooked to a charger through all of this), and we tried new plugs.

One thing I think that I left out is that the symotoms started while it was running. I was checking function of my new turn signals (which I've removed to verify that they weren't part of the problem), it had been running for 15min or so, it dropped idle and died, I restarted it but had to hold throttle to keep it running. It sounded like one cylinder so I gave it some good revs and shut it down...which brings back to the initial post...

This really sucks...

I would check the voltage to the coil(s). The should be two wires to the coil(s). With the key on one will have power from the battery and one will not. I do not know the colors for the wires on your bike, but that is where I would start.
Since your bike is a KZ400, I assume it has points and not electronic ignition. This would be the next place I would look since the points control the spark.
Unfortuately, my KZ750 is different enough from your bike that the 400, 440, 750 twin folks will need to take over.
Good luck.

clean and gap the points. I am having the same problem with my 650 and I seems my points are bad and are burning up quickley and are causing me to loose spark to the 1/4 cylinders.

I entirely re-wired my 77 650 sucessfully last year to clear electrical gremlins similar to the one that you are describing.

Sorry about the budget crunch, but if you do not already have one, you really need to buy/borrow a multimeter. (Mine is from radio shack and is around the 20 to 30 dollar range, I seem to recall there was a 12 dollar one too.) A manual for your bike would be another must have (which I imagine you have already, having worked on it since last August,) fortunately for this project you can download the info that you need from the web, so no purchase necessary.

You have a wiring problem, and you need to find it ala needle in a haystack. So,...

Get the wiring diagram for your bike. Familiarize yourself with every part of it, to the point that you can identify all the schematic symbols and trace power from the battery, through the parts, and back to the battery again.

Use your multimeter to physically search for broken, otherwise open, or shorting wires on your bike. There should be specific voltages on specific wires from specific parts at specific times. For instance the rectifier's green wire should read zero volts with the key off, twelve volts with the key on and 10 -14.5 volts with the engine running....(Post requests in forum for help with your bike's voltages) If you go through and check your system systematically you will eventually happen upon your particular anomaly, and will be able to deal with it accordingly.

This might seem like a major pain in the ass, but the education is completely worth it. Just recently my rectifier caught fire and fried a portion of my wiring. I was able to fix it in an afternoon due in part to my prior work scouring and learning the system, and to the help recieved on this site.

Another thing to do is to post which bike you have. You can have this added to your posts automatically from the profiles upper right from the home page.

Good luck with the project! We will keep checking to see how you are doing.

This assumes that there is no spark.

Post edited by: Qdude, at: 2007/07/16 15:27

Bill already asked... you didn't answer; HOW DO YOU KNOW THERE IS NO SPARK? Are you assuming this since it won't run?

It could be a fuel flow problem with incredibly weak spark... Running then quitting...

Could heat be a problem? Much too lean a mixture? Warming up a wire harness that causes expansion that closes a curcuit via ruined insulation?

Poltergiest?

There is spark...sometimes.

when I pull and ground the plugs I get (as stated) weak and sporatic spark.

I do have a voltmeter, and a manual. I am an automotive technician, I just get a little glassy eyed when I look at a bike. I know everything is connected but haven't checked for power. This will be my next step whenever I can get back out to the shop.

BTW Since I hadn't answered this yet: The shop cleaned the hardcore laquering/sediment from the carbs (7K miles in 30 yrs means it's sat), replaced the spark plugs, put gas in it, filed/set the points, re-jetted the carbs, and inspected the bike.

Added: Sorry, we must have been posting at the same time.


It would be helpful to know what the shop did to the bike incase it involves something that would control or would effect the spark.
Also, how long ago was the service performed? How many miles? How quickly did everything go downhill?
A friend of mine had service done to his bike at a dealer and a few weeks after he got it back he noticed the volt meter wasn't working.
Popped the tank off and the connection was loose. The shop disconnected it to work on the bike and never hooked it back up.

Post edited by: cafekz750, at: 2007/07/16 17:20

Post edited by: cafekz750, at: 2007/07/16 17:24

Look up

They only worked on the carbs, nothing ignition related.