No spark

I recently changed the points on my 1974 850 Commando as a winter maintenance project. When I checked for spark at the plugs after the new points were installed by laying the plugs against the head and kicking the bike over, there was no spark at the plugs. Checked with test light. With ignition on, there is power getting to the coils via the white/purple wires. There is also power from the coils getting to the ends of the black/yellow and black/white wires in the contact breaker housing. Resistance between all connections measured at 0 ohms. But when I connect the ends of the black/yellow and black/white wires to the posts on the respective contact breaker assemblies there is no power. I have turned the engine via the kickstart pedal and there is no spark at the points. I have checked the order of connection of the various parts on the post on the contact breaker assembly several times. The parts, including the plastic insulating bushings and wire terminals, are assembled on the post in the order shown in the shop manual and in my other reference books. It’s almost as if the terminals at the end of the black/white and black/yellow wires are somehow not making contact with the contact breaker springs despite being adjacent on the posts. I suspect I’m missing something embarrassingly simple. Any suggestions for further troubleshooting?

I know you said you checked but be sure you have the coil wires attached below the bushing. If they are above the bushing against the nut they will be short circuited. Also - I have seen modern points not conduct electricity due to deposits/preservative/whatever on the contact surfaces so give the contact a good cleaning. Be sure the point gap is correctly set and the hold-down screws tight so the points can't shift on the plate once the gap is set.

Good Luck!!!

Thanks for getting back. The coil wires are definitely attached below the top bushing. I pulled the contact breaker plate off the bike to do some bench testing. I don’t have a bike lift and my 70 year old knees are making it harder to work on the bike on the floor. With the new points in place on the plate and with the points open, there is continuity across the open points! Not sure how that is even possible. Replaced the new points with the old points and when the points are manually opened, continuity between the points breaks. Again not sure what is going on but it seems to be the new points that are somehow suspect. Can’t see anything obviously wrong with them. Points are a pretty simple mechanical switch. Not sure how you can have continuity across an open switch so it looks like power might be getting to the breaker plate somehow and then to the other side of the open breaker switch. Points mechanism is separated from the plate by small insulators. Maybe the insulators are the issue.

Take one set of points off the plate and check again. If they are still shorted then they are either made wrong or you have the insulator wrong.

New point sets are generally rather poor compared to those back in the day. The new ones don't last as long and it's possible they were not constructed/assembled properly by whomever made them. Compare them closely to the old ones - there may be an obvious and easily corrected answer. Should be related to the bushings/insulator.

I'm not familiar with the points setup on the Commando, but on an airhead /5 it is possible that the points spring can touch the points mounting screw or washer causing those symptoms. I had that happen on a replacement set of points.

Mystery solved. BERT is exactly right. As MexicoMike suggested, I carefully compared the new points to the old ones. The small leaf spring that connects the point terminal with the pivot is slightly more elongated on the new points resulting in the bend in the spring contacting one of the mounting screws on the plate. Some careful fiddling with the spring shape, and problem solved. Big fat blue spark at the plugs. Thanks to all for their suggestions.

WEM said:

Mystery solved. BERT is exactly right. As MexicoMike suggested, I carefully compared the new points to the old ones. The small leaf spring that connects the point terminal with the pivot is slightly more elongated on the new points resulting in the bend in the spring contacting one of the mounting screws on the plate. Some careful fiddling with the spring shape, and problem solved. Big fat blue spark at the plugs. Thanks to all for their suggestions.

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Glad you sorted it. Im also glad I went straight to an EI setup on my bikes.

I have a Trispark unit in a box on a shelf. Almost convinced to install it after this episode.

WEM said:

Mystery solved. BERT is exactly right. As MexicoMike suggested, I carefully compared the new points to the old ones. The small leaf spring that connects the point terminal with the pivot is slightly more elongated on the new points resulting in the bend in the spring contacting one of the mounting screws on the plate. Some careful fiddling with the spring shape, and problem solved. Big fat blue spark at the plugs. Thanks to all for their suggestions.

Click to expand...

Any picture of the packing the points came in?

Any close up picture of the points?

Sorry. Never thought to take any photos.

WEM said:

Sorry. Never thought to take any photos.

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I've seen some very low quality shit for sale