CB175 Getting weird intermittent spark

[boostbaron]

Hey guys, My 1970 cb175 is turning into a nightmare and frustrating the hell out of me. Spark is the issue, it will only spark when i crank it and turn the key up or down in the ignition switch. Lets say the bike is sitting for a while and I pull the plug to chekc for spark/ I ground it to the engine block and hit the starter button. I will get nice blue spark for 3 seconds and it will go out. If i continue cranking the engine and turning the ignition key back and forth the spark will return once every couple seconds. Im only taking out one plug at a time and I am jumping the bike with my car so it has a strong battery source. Im really stumped and this is preventing me from moving along with my build. Any help would be great.

 

[Sonreir]

Is the problem with both cylinders?

Have you checked your timing, point gaps, and health of your advancer?

Check all connections to and from the coils. Use some steel wool or a wire brush to clean up all the connections (especially ground to the frame from the coils and the negative connection from the battery to the frame).

 

[teazer]

175 has a single coil that needs to fire both ends at once. It could be something sneaky like a capacitor breaking down or a coil overheating or it might be that the plug that's left in is fouling. If one plug fouls the other cannot fire.

Take both plugs out and use to simple cheap spark testers or put two clean plugs in the caps and lay them on the head and hit the button.

Don't keep it on for more than a few seconds or things start to overheat.

 

[AlphaDogChoppers]

Could be bad condenser.