One Cylinder not Firing

Second from Left is not firing. Bike sat for 3 weeks with only one run around the block to break it up. When I fired it up, it ran like it was not firing all 4. I charged the battery, it was low.

Full charge and still no fire. Can coils be the problem? The wires look ok, it has new boots and plugs within the last 3 months.

How do I check the coils or what else should I look for?

What model bike are we talking about ?

Remove the lead from plug no 1, place an old plug in the unconnected lead and let it lie on the engin. Start the bike up, use a dry cloth to hold the base of the plug a half inch away from the engin - reving the bike - you should see a nice arcing spark (night light gives a great picture, strong sun light can make it hard to see the spark)

If spark is present, replace the lead and move to plug no 2, and continue until the dead spark is located.

Remember this checks for spark and does not check the operation of your fitted plugs.

1978 kz1000 a1 is the bike. Once I have located the spark plug not firing, i am pretty sure it is number 2, how do I determine what is the cause and are there multiple factors? Is it typically just the coil going bad? They are original coils.

Got a spare plug to throw in it? Maybe at least pull the plug and clean it, check the gap...

The KZ1000 has 2 coils and it is very rare for only one side of the coil to go defect. It is much more likely you have a bad plug, bad lead or bad cap - this is also the most likely order.

Good luck !

Trey, To determine WHICH plug isn't firing, get a spray bottle with water. If you spray water on a pipe where the cylinder is firing, it will just evaporate with a sizzle. If you spray on a non-firing cylinder, the water will sizzle but run off the pipe to the ground. This is a little better way of figuring which cylinder isn't firing that sticking a finger on each pipe.

Now, the cylinders are numbered 1 through 4 counting left to right as you sit on the bike. Not sure which way you were counting but let's say that the #2 cylinder is the non-firing guy.

The coils fire in pairs. 1 and 4 plugs fire off one coil and 2 and 3 off the other. To tell which coil is which, you can either work back from the plug wires or look at the ignition wire connected to your coil. The 1&4 coil will have a BLACK wire from the ignition and the 2&3 coil will have a GREEN wire.

Anyhow, if your #2 cylinder isn't firing, first step is to swap the #2 and #3 plug wires. If the problem MOVES, you know that you have a bad plug wire, bad connection or bad cap. If the problem STAYS on the #2 cylinder, you have a bad spark plug (if ignition related) or mechanical issue, such as valves or rings or the carbs.

Swap the wires and see if the problem moves and we can go from there after ascertaining WHICH cylinder isn't firing.

Thanks! i will try this method tonight!!!

Ok, swapped and #2 still not firing. Replaced the plug, actually all of them, problem solved.

Thanks for the input!!!!!

Hope you got a sense of how to trouble shoot this fairly simple issue. If the plug fouls again, that will require further work I guess.

I can't tell if you have determined that there is no spark or not. I had a case of #2 not firing, and swapped plugs; no change (did the sizzle test). Saw that there was spark, chased my tail for quite a while.

Finally found out that it was the fuel petcock. Yup, the diaphragm had a hole in it, so gas was running straight from the tank to the intake of #2, which supplies vacuum to the valve to actuate it.

Once I put a rebuild kit in the valve, #2 started to fire after a bit. Blue smoke like you would not believe. Now the bike runs better all around, as the bad petcock was also not letting quite enough gas through, so cylinders 1, 3, and 4 were running lean or intermittently.

Whole new bike! Plus now I don't reek of unleaded.

May not be your problem, but it's easy to check.

--Lyle