Negative-Ground Boyer Diagnostics

I've got a late Triumph Boyer system installed on an 850 Norton Commando with 6V coils--the bike was converted to negative ground. The red Boyer wire is connected with the hot 12V lead on the positive side of one coil. The negative side of that coil is connected to the positive side of the other coil--the black Boyer lead is on the negative terminal. The white Boyer lead is connected to ground all the way back to the battery.

The black Boyer terminal switches off as it should, showing 0-12V when kicking through. The other coil shows switching when kicking through as well, but the voltage never drops below 6V. The bike jusr soddenly kicks through and backfires explosively every twenty kicks or so. Coils, wiring, stator, rotor and box have been checked out extensively and seem to be working fine--in fact, the bike was running very well with this wiring setup. The timing was dead on and hasn't been changed.

Any idiosyncrasies peculiar to the Triumph 12V negative-ground Boyer setup that I'm missing?


Tim Kraakevik
kraakevik@voyager.net
Three Commandos

For what its worth, I recently had a similar experience with the backfiring. The bike quit while on the freeway, but that is another story. What I ultimately found was the solder where the wires go into the pick-up coil plate broke off so no spark signal was getting through to the pick-up coils. If you haven't done it, carefully check where the wires solder to that plate. Just a thought.

According to a Triumph "expert" the Triumph 12V Boyer doesn't have the problem with the stator coil wires breaking. Many Commando owners running a Boyer have posted those wires breaking. The problem with the Boyer is that the wires are soldered. Soldered connections are a no-no in any automotive or motorcycle manufacturing I'm familiar with. The solder wicks up the wires and they become brittle, prone to break with repeated flexing from vibration. In many cases, they break inside the insulation, so you don't see the break. The fix is to replace the solder connections with two small screws and nuts. Terminate the wires with the proper sized ring connectors that are CRIMPED. Problem permanently solved. I would bet many of the carburetor problems turn out to be the broken Boyer pickup wires.

JimC said:

According to a Triumph "expert" the Triumph 12V Boyer doesn't have the problem with the stator coil wires breaking.

Click to expand...

Well, a "Triumph" Boyer wouldn't have that problem when it's fitted to a Triumph as the engine isn't shaking around in the frame! But both the "Triumph" and "Norton" version Boyer ignitions use the same (N.T. 1a) stator.

Gentlemen

The resistance readings on the coils and stator are fine; the rotor has adequate magnetism; there's continuity on all wires, including the coil leads. Both coils have been substituted for working units, as have the plugs. The black box is switching satisfactorily on the coil to which it's attached. I'd appreciate some advanced diagnostics on this--many thanks for your help



Tim Kraakevik
Riding Norton twins since '64