One cylinder not cutting out

So I recently took my engine out of my 76 kz750 twin due to my kickstart failing, and after fixing that problem and getting it back in only one of my cylinders is firing consistantly. The other will pop and fire and cut out and back fire and all that jazz. If I open the throttle a little it seems to not be nearly as bad. Ive taken the carbs off cleaned them, checked the timing, recently checked and regapped the valves, checked the voltage comming off my dyna S ignition and it was fine, and the only thing I can come up with is that the coil is bad. It's a wasted spark system though and the other cylinder fires just fine. Anyone know if it is possible that the coil could be bad? Its the original coil too.

KZCool wrote: So I recently took my engine out of my 76 kz750 twin due to my kickstart failing, and after fixing that problem and getting it back in only one of my cylinders is firing consistantly. The other will pop and fire and cut out and back fire and all that jazz. If I open the throttle a little it seems to not be nearly as bad. Ive taken the carbs off cleaned them, checked the timing, recently checked and regapped the valves, checked the voltage comming off my dyna S ignition and it was fine, and the only thing I can come up with is that the coil is bad. It's a wasted spark system though and the other cylinder fires just fine. Anyone know if it is possible that the coil could be bad? Its the original coil too.

Possible erratic spark, perhaps from a bad plug wire leaking voltage to the engine head.

Could remove both plugs, tape them together (or hold both against the engine head) and assess spark quality while spinning the engine over.

Good Fortune!

I'd replace both sparkplug caps as they contain a 5000 ohm resistor that over time can go bad, making for erratic spark at the plug. Tried another brand of sparkplug? I've found that some of the US made NGK's are not as good as the ones made in Japan.

MFolks wrote: I'd replace both sparkplug caps as they contain a 5000 ohm resistor that over time can go bad, making for erratic spark at the plug. Tried another brand of sparkplug? I've found that some of the US made NGK's are not as good as the ones made in Japan.

Thanks a ton for the advice. sure enough I checked the resistance of one of the caps and it was 5 something kilo-ohms and the other was infinite, just ordered some new ones from Z1 so I should be riding in 2 days. Thanks again.

It's a simple test & cheap repair when you get a miss like this. I always check the sparkplug caps before tearing into the carbs.

These 4 strokes need but four things to run:
1.Compression
2.Clean air
3.Fuel
4.Spark

If any of the above are not there, the engine will not run.

I just got my caps from Z1 and the same thing is happening. I dont think its the carbs but it might be. The one cylinder runs great all the way down to below 1K so it wouldnt be the timing thats off or it wouldn't run that well at that low of an RPM. and the other doesnt fire at all untill I rev it a little. The piolet screw had no affect on it, but when I started it with the "choke" or fuel plunger open, both cylinders fired just fine.

Did the engine run fine before fixing the kickstarter, if so I would say it has to do with something related to repair.

If you haven't already done so, make sure the connection of the plug wire to the coil is good.

Yesterday my dog ate one of my plug wires. I replaced the wire (dyna coil) and the bike was running cruddy at idle. I thought something had clogged the pilot jets and I cleaned the carbs. That didn't fix the problem and then I realized the connection from the plug wire to the coil was not 100%. With that fixed, the KZ runs like a champ - even better than before with the freshly cleaned idle circuits.

Ill look into the leads. The spark plug wires come straight out of the coil though so im not sure what to look for. And it did run fine before but the only thing i had to do in the end was replace the retaining ring on the kick shaft. Didnt need to take my eninge out after all :pinch: . What doesnt make since is if its a spark problem, why would it run better with the choke on? Just strange.

Patton wrote: ...Could remove both plugs, tape them together (or hold both against the engine head) and assess spark quality while spinning the engine over....

Do both plugs show fat blue sparks?

Good Fortune!

Given acceptable compression, correct valve clearances, and a healthy properly timed spark, could then look to an issue in the carb pilot circuit (perhaps the passageways are still not yet sufficiently clean).

Good Fortune!