Topic: 1972 barn find need help

[Xkylescorex]

A few weeks ago I picked up a nice gold 72 cb750 at an estate auction for $700. I usually chop old jap bikes but this one is too complete and nice to cut up. Ive had a few old beater sohc but they always ran. I need some help with this one.

1. No spark!
 Th starter button was missing from the controls so I bought a new one from 4into1.i replaced it and now I have all my lights but when I hit the starter nothing happens. No clicks nothing. I have it in nuetral.
 I can jump the startermotor at the solenoid but even though the engine is turning I get no spark. I do have some points and condensors to put in but I would like to get the starter sorted out.

When the engine is turning over the points spark erratically.even if its not timed right shouldnt I get a spark at the plug?

I was told to run a jumper wire from the coil where it goes to the points and ground it to the frame to see if I get a spark to test the coil. The jumper cable sparks at the frame not at the plug. So there is ppwer running through the coil but its not sparking at the plug. Does that mean anything? Just trying to knock things out one by one.

Here she is

[calj737]

You have a couple of issues most likely due to neglect.

The START button is a ground signal to the solenoid (Yellow/Red wire on RH control). Locate where it comes from handlebars and test continuity to ground with a meter. Then go to the solenoid, repeat the test. And then ultimately, make sure the handlebar Y/R has continuity to the solenoid Y/R. You'll probably find a wiring issue along the way.

It could also very well be the button itself needs repair/maintenance. If the wiring deposit resolve it, open the control and inspect and repair anything inside.

Your coils: there's a BLK/WHT striped wire feeding power to the coils. Each coil has its own wire and the coils join together in a double female bullet connector. This is fed power through the KILL/RUN switch. Use your meter and confirm you have 12v at the connector. You also need to confirm the battery is fully charged and known good with voltage above 12.4v to start the bike.

A lack of spark at eh plug could be your points, condensers, or even the plug caps themselves.ey go bad after time, and each cap unscrews from the plug wire. Use yur meter and read the resistance of each cap (probe on either end). Ohms should be 5k, no higher than 7k Ohms.

[toytuff]

Nice buy!

[Xkylescorex]

Well the button is new so thats good. I have 12v going into the coil. It could be the plug wires. Everything is old and corroded. Bike has a tag that says 1990 so its probably been sitting since then. Tge coils look like the wires are built onto them not the kind with a cap and a screwin plug wire. Is there a way to fix old wires that are made like this?

[ekpent]

The wires are molded into the coil but the plug caps screw off. The coil being the only reason your not getting spark is pretty remote,they are fairly stout.

[Tews19]

That is a nice buy.