I have a 71 CB350 that has suddenly decided not to fire on the left side. I pulled the plug and while holding it away from the block it will spark like mad. As soon as I ground it to the block I get nothing. I recently set the point gap and valves but I don't think this would cause the problem I am seeing. Any thoughts would be greatly appreciated. Thanks

That's odd. Usually NO spark when away from block (Electric needs a path to ground).

I can't see where the spark would be going to.....When the spark jumps the gap, it has to go to ground. If it is in the air, and you are not getting shocked, it seems there is something missing in the description.

Maybe someone else has seen this...

The only though is the spark plug wire insulation is conductive, but that still wouldn't explain it going away.

Another thought, try a different plug, maybe the one you have is grounded internally, and is sparking somewhere besides the tip. I have seen that before. A crack in the porcelain under the metal nut area that is not easily seen.

Plug is internally shorted...When off the ground, the spark will jump and show, but when grounded the path is already completed, no need to jump...

Thank you for the replies. I will pick up some new plugs and keep you posted on the progress.

So the spark plugs did the trick who would have thought. Now as Paul Harvey sais heres the rest of the story. After picking up and gapping the new plugs I grounded it against the case and I got good spark. So I went to install the plug and dropped it on the floor. I picked it up not thinking much about it and went to install it. It started kind of tough so I put the ratchet on it
I began to ratchet it in and it got tougher so i decided to back it out. I had apparently damaged the threads when I dropped it. Well I had totally destroyed the threads at this point but tried to clean them up with a tap. Threaded the plug back in and went to torque it and it spun free So I went and spent $40 on a heli coil and got that installed along with a new plug. Bike fired right up and everything was fine. Of course I want to take it out for a test run so go to back it out of the garage maneuvering around the wifes car. While i was watching her car so I didn't hit it I caught the tail light on the door frame and smashed it. But I got it out and it ran great. Time to order a new lens. Thanks again for the help.

I've had those days......ugh...makes you want to cry sometimes..

i have had something similar. i found my bike running on one side only so i tested the NEW plug - for me, when not grounded to bike, the spark jumped from the plug to the bike. i could hold it almost an inch away and see the spark jumping that far. but once i touched bike spark disappeared.

after reading this post, i put in one of the old plugs, started it up, but then i was getting the spark. yikes!!!! nothing wakes you up more then that. i put on pair of rubber gloves and tested plug, back to normal. touch bike=spark, no touchy=no spark.

i need to look into why i was getting sparked from holding the boot. hmmmmmm.