boyer mk3 stator plate fail?

the old girl is firing on one and sometimes on both. went through everything, as usual blamed the carbs, noop! their clean,
6v coils tested ok, mk3 boyer box sparks, but i'm only getting 65ohms across both wires to the stator plate. according to the info i can find the mk4 stator plate is suppose to be ~138ohms. is that the same for the mk3???

thanks

Check for broken/shorted wires associated with the stator. The vibration will sometimes fatigue the wire inside the insulation or possible rub through the insulation. The clue that you have about half the resistance tells me to look for a short to ground on one of the wires. I've always embedded the wires in gum puckey of some sort to keep them from vibrating.

FYI, early Mk111 stator coils were only 33ohms each, so you may be reading correctly. Try measuring each individually. Then with a meter clipped to the bullets, wiggle the wires around and watch the meter. If it goes open circuit, the copper strands have broken inside the cables.

The magnets perhaps?

Going to fire only on one cylinder is unlikely to be the Boyer as it's wasted spark. The Boyer acts as a single set of points, the 2 coils are to equalise the 2 firing points to 180 degrees apart. When I had these symptoms I fixed it with a dedicated earth wire from head back to battery. So on mine the original earth was going bad in the harness and only carrying enough energy for one spark. It favoured the right side with the left misfiring most. The clue was if I removed either HT lead the other fired 100% until the other sides HT was replaced, this was after a week on new coils, HT leads, spark plugs and a Boyer.

As Kommando says, don’t rely on frame or casings for the return part of the low tension circuit.

Also suspect the live side of the circuit: ignition switch, kill switch, fuse holders, connections, crimps. Test by hot-wiring the Boyer to the battery (a good fully charged battery!).

kommando said:

Going to fire only on one cylinder is unlikely to be the Boyer as it's wasted spark. The Boyer acts as a single set of points, the 2 coils are to equalise the 2 firing points to 180 degrees apart. When I had these symptoms I fixed it with a dedicated earth wire from head back to battery. So on mine the original earth was going bad in the harness and only carrying enough energy for one spark. It favoured the right side with the left misfiring most. The clue was if I removed either HT lead the other fired 100% untill the HT was replaced, this was after a week on new coils, HT leads, spark plugs and a Boyer.

Click to expand...

I just went through the same symptoms on my Boyer ignition system with the 72 roadster firing on both cylinders then going back to right cylinder then nothing after. We put it down to the Boyer trigger plate and replaced that and both cylinders came back on line. I wouldn’t call the spark very strong on both plugs so I will try the extra earth from head back to the positive battery.
Cheers

Oh, and I have a brand new & improved stator plate for sale in the ads section.

850commando said:

the old girl is firing on one and sometimes on both. went through everything, as usual blamed the carbs, noop! their clean,
6v coils tested ok, mk3 boyer box sparks, but i'm only getting 65ohms across both wires to the stator plate. according to the info i can find the mk4 stator plate is suppose to be ~138ohms. is that the same for the mk3???

thanks

Click to expand...

I had that symptom.
With the engine idling on the main stand, reach in and grab the wires where they leave the frame and go into the back of the timing chest. I could make the misfire happen by jostling the wires.
Replace wires, RTV into the case, and a travel loop before being tied to the frame.

update; i removed the stator plate and as per cliffa comments, both coils ohm out at ~33ohm. screw driver on the magnets was not very assuring ( i didnot remove the magnets plate,) as theres a shit load of work to retime the whole thing if good or bad. im running bpr7es plugs, so the plug caps are none resistor, with wire and caps i get 0 ohm, the coils were 1.7ohm , test fire by connecting the b/w -b/y at the box and i get spark on both plugs,

went back to the carbs, pwk's and ran a double check on the pilot circuit, the opening is round and i can see through it , i put the pwk's on because i couldn't get the amals to run right, and at first the pwks ran fine, very low mileage on the pwk carbs, but the boyer has been on there for a long time

next step i think is to add fuel and try again, had a chat with john at motoparts in Edm/ab. he sells boyer and vape ignition. anyone out there running the Vape? comments on the vape?
thanks

I run vape for past 7 seasons, very happy. It is basically an improved boyer, epoxy encapsulated stator plate/wires so no flex damage.

I have used a Vape (or Wassell) ignition on another well-known British twin for about six years. It appears to behave like the analogue Boyer and does look stronger-made than Boyer.

Did 125 miles on it today.

okay so going back to the original question, we have an answer, and sad to say i've been chasing this little sh!t for over a year, i went back thought the carbs a second time and then started with the electrical and discovered a plug that would not fire.....

so if its a Norton and won't run,don't blame the carbs, check the boyer mk3 and your plugs....

have a nice day