Boyer, Electrical, or Madness?

I recently discovered that the timing marks on my primary cover were off by 7.5 degrees. After retiming my ignition (Boyer MKIII black box) I thought I was out of the woods but I am still having problems. After two 1 hour rides, I intermittently experienced a few backfires and an occasional misfire. If I had to give a frequency, I would say there were about a dozen or so of these events during each of my one hour legs. There did not seem to be anything unique about the circumstances around these events, and usually it was only a pop or two that quickly smoothed out.

Upon advice received elsewhere, I bypassed my key switch and kill switch by running a wire from the negative terminal of the battery to the Boyer with a toggle switch to turn it off and on. I started the bike but it was popping and backfiring. I rode it around the block and it bucked and misfired somewhat regularly.

What I have done:
-New Amal Premiers (not an expert but am confident they are set up correctly, I.e., no swarf or detritus in bowls; #19 pilot jets clean and turned all the way in; air mixture screws adjusted from baseline 1 1/2 turns; slides synced; new gaskets and insulators, manifold connections not overtightened; no air leaks)
-New battery is strong
-New capacitor
-New plugs
-Tested coils and numbers reported on the forum were not thought to be out of bounds
-Valve clearances are correct
-Checked Boyer wiring to coils and checked ground
-Checked and confirmed ground from battery to frame
-Timing is correct and is set at 30 degrees fully advanced (revved up past 5000 rpms)

I think it has to be electrical with the symptoms I described. And I think after bypassing the key and kill switch, the Boyer is the number one suspect. I am happy to look elsewhere, but I don’t have any other ideas of where to look.
It’s a ‘73 Roadster. The bike is candy apple red if that makes any difference.

Thank you.

Check the leads of the Boyer at the stator plate. They get brittle and crack.

MichaelB said:

Check the leads of the Boyer at the stator plate. They get brittle and crack.

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Yes. And can be very tricky to detect. Use a muktumeter and pull firmly on the wires. They can look good and test OK until put under stress. I tested mine several times and they checked out OK until I really twisted the wire. Resoldered the wires and problem gone.

johnm said:

Yes. And can be very tricky to detect. Use a muktumeter and pull firmly on the wires. They can look good and test OK until put under stress. I tested mine several times and they checked out OK until I really twisted the wire. Resoldered the wires and problem gone.

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I let the engine idle, wiggled the wire by hand, caused the backfire.

I had the same.

Spent some weeks trying to solve what I was convinced was a carb problem, before finding the damaged backplate wires !

Not on a Boyer but on my Lucas Rita fitted to my t140e I had rough running for months until I traced it to slight corrosion on one of the bullet connectors on the pickup wires

Snortin Vache said:

It’s a ‘73 Roadster. The bike is candy apple red if that makes any difference.

Thank you.

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I believe the red ones were notorious for this.

Seriously, if it isn't the Boyer leads breaking up on the stator plate - which is certainly a known issue (they can fracture inside the insulation), it could be contamination getting into the carbs and fouling the pilot jets - the popping could well be a symptom; i.e. lean running, especially if it occurs at the lower end of the rev range.
Is the tank clean inside?
I found out the hard way that fuel filters won't catch particles big enough to block a pilot jet, but a magnet on the bottom of the tank adjacent to the tap will collect any metallic debris.

Snortin Vache said:

Upon advice received elsewhere, I bypassed my key switch and kill switch by running a wire from the negative terminal of the battery to the Boyer with a toggle switch to turn it off and on. I started the bike but it was popping and backfiring. I rode it around the block and it bucked and misfired somewhat regularly.

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Bypassing the ignition and kill switches certainly should not have made things worse.

Snortin Vache said:

-Checked Boyer wiring to coils and checked ground
-Checked and confirmed ground from battery to frame

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Harness red is 'ground', not the "frame", therefore, the Boyer box and coils both need to be connected to harness red in preference to the frame (normally by using the original red condenser pack earth/ground wire).

The first go to with the Boyer for me is the pickup plate wires....and I've seen a few poorly mounted black boxes (boyer) have had broken wiring where the wires a resin into the box...
Get them sorted from the word go and there reliable as....

As others have mentioned, the wires on the Boyer stator plate are known to fracture inside the insulation and make intermittent contact. See this thread for more detail...

It sounds as though it is probably an electrical problem. If it isn't, you need to go throught thev sequence and re-tune your carburetors. Do not rely on tining marks and other peoples' jetting suggesdtions. Set up your ignition sysrem with a degree disc, then jet to suit it. Start rich and lean-off progessively. Do not continue to ride a bike when the motor misses. Stop and raise the needles.

I removed the stator plate and found both wires had a tiny crack in the insulation right where it came out of the sleeve held down by the zip tie. The strands of both wires were still intact, but I think that when it vibrated it must have occasionally arced across the two leads and caused the misfiring.

I did not follow your good example Cliffa, but instead snipped the wires, used a Dremel to clean off the epoxy, drilled out the wires, and renewed what was originally there: soldered ends on the back, a heavy-handed dollop of epoxy on the front, a zip tie, and a piece of heat shrink to sleeve both wires together. After about a thirty mile ride I did not a single misfire or backfire, so I think that sorted it. Thank you all for your suggestions.

Snortin Vache said:

I removed the stator plate and found both wires had a tiny crack in the insulation right where it came out of the sleeve held down by the zip tie. The strands of both wires were still intact, but I think that when it vibrated it must have occasionally arced across the two leads and caused the misfiring.

I did not follow your good example Cliffa, but instead snipped the wires, used a Dremel to clean off the epoxy, drilled out the wires, and renewed what was originally there: soldered ends on the back, a heavy-handed dollop of epoxy on the front, a zip tie, and a piece of heat shrink to sleeve both wires together. After about a thirty mile ride I did not a single misfire or backfire, so I think that sorted it. Thank you all for your suggestions.

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Nice Job!!!

Snortin Vache said:

I removed the stator plate and found both wires had a tiny crack in the insulation right where it came out of the sleeve held down by the zip tie. The strands of both wires were still intact, but I think that when it vibrated it must have occasionally arced across the two leads and caused the misfiring.

I did not follow your good example Cliffa, but instead snipped the wires, used a Dremel to clean off the epoxy, drilled out the wires, and renewed what was originally there: soldered ends on the back, a heavy-handed dollop of epoxy on the front, a zip tie, and a piece of heat shrink to sleeve both wires together. After about a thirty mile ride I did not a single misfire or backfire, so I think that sorted it. Thank you all for your suggestions.

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A bit of foam rubber in the cavity has helped keep it from reocurring

Great to hear!

Looks like you won't need a respray after all

Commando's don't vibrate

ashman said:

Commando's don't vibrate

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No, but the engine "shakes like a whore in church"

If you read the period reviews, they were turbine smooth.....