500 Two-Stroke Tech

Hello everyone, I am having a problem with my RZ500 and looking to see if any other members have experienced the same problem I am currently having. The bike will start up cold and seem to run well. After approximately 10 minutes after it warms up and gets hot it will seem to miss Run lethargically And die out. It will not restart. I’ve pulled the plugs out at this time and there is absolutely no spark whatsoever. Hours later you can restart it in the cycle will repeat itself. I’ve tested the stater coil and it was .4 ohms the pick up coil was 122.7 ohms and the source coil Red and green wire was 162.6 ohms and the brown and red wire from the stater harness was 18.8 ohms. The electrical harness on the bike is clean and all Connections seem to be tight. Absolutely everything on the bike electrically works fine as well. I am at a loss with this problem and just wondering whether anyone has experienced anything like this. Thank you for anything you could provide me with. Regards, Ron.

Not to mention I sent you a spare CDI box and that did not stop the issue.

Or you have 2 faulty CDIs. It does sound like a cold solder joint.

I should have said bad CDI at first but I understand you have a spare CDI and same result.
So you should try this :
Start your bike with first CDI and warm it until it dies.
At this moment, swap your CDI and try it, if bike runs then you have two faulty CDIs !
If bike doesn't run, problem is most likely in the stator.

Once the motorcycle died out I replaced it with the second CDI and it still would not start. The following morning it started right up and repeated the Same process. It would start up run Real crisp and I could stop at intersections without it dying out and then after about 4 miles of driving it would act like it was missing and run real poor as if it wasn’t running on all cylinders you would come to a stop and after about 10 seconds it would die out and not restart. All the manifolds were hot so it was definitely running on all four cylinders but if I removed the spark plugs and check for spark there was nothing at all. Like I said before leaving the bike untouched you could start it the next day and it would run and repeat the same process. So frustrated with this issue!

Ok.
So check the resistances of the stator and pickup coil when motor dies.
I suspect you have a defective isolation of the wirings.

Normally you need to meter the stator cold. If you do it hot the readings won't be accurate. However, if Philippe is right it won't matter because the stator should show an obvious failure.

OK thanks fellas. I should have stated that I already did that. These are my COLD READINGS. .4 ohms Stater coil. Pick up coil 108.1 ohms. Source coil red/green wire 140.8 ohms. Source coil brown/red wire 18.6 ohms.
HOT/NO START READINGS. Stator coil .4 ohms. Pick up coil 122.7 ohms. Source coil red/green wire 162.6 ohms. Source coil brown/red wire 21.3 ohms. Thank you so much for all the help you can provide for me. Regards, Ron.

To me those numbers seem ok for cold and hot. About what would be expected. The hot numbers should be higher, and they are, but the numbers don't appear to show an obvious fault. In fact, the numbers for hot and cold are all within the cold spec +/- 20% as required with the exception of the R-G source coil, which reads only 10 ohms higher than the max cold reading, but for hot it's fine. Any failure should have been obvious when metered.

It couldn't hurt to swap out the stator if you have one, but from the numbers you've given it doesn't appear to be a stator problem. At least that is my view using my limited knowledge of the subject.

From the first post I'd have said CDI or source coils.
But having two faulty CDI's with exactly the same symptom is close to impossible.

That leaves the source coils as main suspect.
Try to cool down the stator after the engine died. I use stuff like this

https://www.reichelt.de/Cold-Sprays-and ... stct=pos_0" onclick="window.open(this.href);return false;

If it starts after cooling down, you have a bullet proof evidence.

In any case my advise for repair is a PDCI from Zeeltronic. The DC CDI eliminates both possible causes at once AND adds more performance than a decent set of pipes at comparable costs of used parts.

How about the key switch? Could a worn out switch break the connection ?
After getting warm and riding.

+1 on the coils. They can do some weird s!%t when they are failing. These parts are around 33 years old and the internal coil insulators are basically varnish. Sometimes that coating can develop small cracks, small amounts of moisture can collect inside the coil housing and cause odd issues. Just a thought?

Thanks for your input fellas. I will just keep plugging away at this issue until it’s resolved. I am beginning to lose hope. Never have had such a frustrating problem before

Try repeating your tests with the fuel cap removed. You could be dealing with a bad vent in the cap. Depending on how much fuel is in the tank and the degree of restriction in the venting, the bike could behave just as you describe. The spark on the RZ is notoriously hard to observe on a good day. The blocked vent will not hold vacuum indefinitely and will allow the carbs to refill over time.

I also thought about defective venting but assumed there was no spark at all on four cylinders.