help needed with spark problem.

[rufio]

OK.....so we are tearing hairs out of our head here.
My buddy owns a little 1971 Yamaha CT1. We were running around town one day and in to the hills when he lost power and weak compression. It also had very very weak spark.
So we bored and honed top end. Everything is good there, but when we kicked it over we weren't getting any spark. We changed the coil and bypassed the ignition. Here's the thing.... when there is no plug boot, there is crazy blue spark coming from the wire sans boot. When we put the boot on there is no spark coming from the plug. We tried a number of plugs and boots, but they are still the same result. Way the heck is up here? We are at wits end. Something simple probably.....what do you guy think?

 

[firebane]

Pull the plug boot off and measure resistance.

 

[rufio]

My buddy measured 3g ohms.

 

[xb33bsa]

points are good and gapped ?

 

[Not_a_sunbeam]

I believe the coil needs to be grounded by the fastener to the frame. the engine has to be a good path to ground. You're almost there, spark at the end of the plug wire.

Another thing that comes to mind is the secondary. If it has been changed to a modern carbon core, the wire might have too much resistance to jump the spark gap.

 

[rufio]

Points are brand new and everything gapped......we'll check the grounds and make sure everything is legit.. I gave up helping him after a few hours. I was pissed. I'll help him again tomorrow, and I'll post on findings. Thanks gentleman!