1972 R75/5 SWB Toaster/Coaster Mystery

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schrader7032
Posts: 7137
Joined: Fri Oct 27, 2006 3:00 am

Re: 1972 R75/5 SWB Toaster/Coaster Mystery

Post by schrader7032 »

So you have 12v at the input to the coils, but have no spark. That would mean that during a rotation of the engine, say by hand, the 12v at the coil remains for all engine rotations. The only way you get spark is if the 12v goes to 0v when the points open. If you never see 0v, then something is wrong with the points...they aren't opening and closing.

There was a rash of bad points units made by a Chinese company...the rubbing block was too tall and never allowed the points to close. Could that be part of the problem?
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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weberkane
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Joined: Sun Dec 04, 2011 7:39 pm

Re: 1972 R75/5 SWB Toaster/Coaster Mystery

Post by weberkane »

Turns out, the points were not working. I replaced them about 9 months ago, they had less than 1000 miles on them and no visible defects so I didn't suspect that they were the problem. Thankfully, the pros at our local BMW shop, Valentine Motor Works went through the ignition wiring, found the points problem and installed new points and condenser. While they were at it, they cleaned up my new Bosch coil installation and replaced spark plug caps that tested out of range. I'm happy to be back on the road with a few months of good riding weather ahead. I clearly need to work on my multi-meter and test-light troubleshooting skills. Thanks for all the helpful suggestions and encouragement. Kevin

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schrader7032
Posts: 7137
Joined: Fri Oct 27, 2006 3:00 am

Re: 1972 R75/5 SWB Toaster/Coaster Mystery

Post by schrader7032 »

Glad you reported back and that you have the bike back on the road!!
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

srankin
Posts: 23
Joined: Fri Jul 14, 2017 8:45 pm

Re: 1972 R75/5 SWB Toaster/Coaster Mystery

Post by srankin »

Glad to hear you are back in the riding business and not the search and repair one. Thanks for letting us know what you found.

Safe rides, have fun, St.

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