bad spark right side

My BSA 650 Firebird 1969 starts left side only. The right side does not fire. If I pull the plug wire about 1/2 to 1 inch away from plug, it starts working. I have to hold it there. If I connect it as it should, it fails. I changed wire, coil, no change. What explains this situation? I have a Boyer ignition.

Have you tried changing the offending sparkplug to a new one ?
Or swapping the plugs, side to side, and see if the problem changes sides.

Getting the hi-tension plug lead away from the plug is an old trick to make a faulty plug fire - effectively you are vastly increasing the dwell, so the coil builds to a massive voltage before it puts out a spark that will frazzle anything. It increases the loading on everything though, they cannot operate like that for long...

P.S. Have you tried doing a compression test on the side that is not firing - if the compression is weak, it can be difficult to make a plug fire effectively in those conditions, and no amount of playing with the ignition side of things will help. It may be as simple as tight valve adjustment, or the rings may be worn or broken...

Hopethishelps.

PPS. I have had an electronic ignition, not Boyer, that went cactus on one side, although in theory they fire both sides to always give a wasted spark - so don't entirely rule out this possibility yet ? There is a power transistor for each side ??

And finally, if you have an airleak or blocked jet, or non-operating choke, on the carb on the side that is not firing, it may make it difficult to start when cold. Check the fuel situation on that side.

Ain't old bikes fun - lotsa things and systems have to work to be all good....

gayf said:

If I pull the plug wire about 1/2 to 1 inch away from plug, it starts working.

Click to expand...

Classic sign of a fouled plug. Put new plug in.

Is the old plug sooty or oily?

You are both correct. I changed the plug and the bike works fine. Thank you very much for your input. François.