Single carb setup runs on one cylinder

kommando · 2026-04-11T02:25:32-0600

Jacko said:
ut still I would assume if that is an issue, the problem should change to the other cylinder when switching the ignition cables, shouldn't it?

The 2 coils on the stator are not engine cylinder specific, the Boyer system is wasted spark and is a single switch unlike points which are cylinder specific ie two switches, the two stator coils signals are averaged to create the timing point so both sparks are timed the same. So when the wires fail or the box fails you lose both cylinders sparks. The one exception is the faulty earth route which limits the flow so there is only enough current for one spark, that is not a Boyer fault. I put a piece of foam over the top of the wires under the timing cover so the wires are not moving with vibration.

cliffa · 2026-04-11T02:42:53-0600

Jacko said:
I replaced the connectors with flexible shrink tubes, but I left the tie in there (photo follows on monday). An ohm-test between the two cables looked good. I will have a look, if there is some damage to the cable already. But still I would assume if that is an issue, the problem should change to the other cylinder when switching the ignition cables, shouldn't it?

I changed the black box because I read of the low voltage problem and she was hard to start at all when not constantly charged by a battery charger. The starting is definitely better now but looking at the photo of the plate I regret that I didn't buy a set to be honest.

As I said I keep you updated with harder facts on monday.

Aha, gotcha, I re-read your post and realized you’d already changed the connectors, however, it’s definitely worth checking those wires as they may already be compromised. I think they are the single most common failure on Boyers in Commando’s due to the Isolastics. Have a look at one of my old posts here..

Thread 'Almost Stranded'

Dec 29, 2017

I was a bit bored today, as my kids have gone back home and my wife was at work. Bike riding is out at the moment as there is about 5 inches of snow outside. So I thought what can I quickly do in the freezing garage? Ideally I want to take a bit off the bike and check or refurb it in the house. Ah! The Boyer stator plate wires. As I’d had a mystery complete engine cutout at the top of the Klausen Pass in august so this was on my “things to check over the winter” list. Right, so out to the garage then. I opened the points cover and saw a sticky label with name “A. Woods” (a former owner...

I realize this is probably nothing to do with your original question, but still definitely worth checking.

lazyeye6 · 2026-04-11T11:06:23-0600

Boyer is a lost spark ignition. Both plugs fire simultaneously every time triggered. A single carb rules out carburetion as a problem.
Switch coils from right to left. Does the problem follow to the opposite cylinder? Use new spark plugs. Even new out of the box
can be a bad plug. A visual “good spark” doesn’t mean good enough to fire the cylinder under compression. Test compression.
Check valve adjustment. Please do replace the pick up plate. Are both coils 6V? Use multimeter to check that their Ohms of resistance meet Boyers
suggested specification.

seattle##gs · 2026-04-11T15:18:44-0600

If no improvement by Monday then wrap up the hole thing and pitch it in the bin. Buy a Tri-spark. It may not solve the problem but now you have a new Tri-spark. And always...have the battery in top condition.

Single carb setup runs on one cylinder

kommando

cliffa

Thread 'Almost Stranded'

lazyeye6

seattle##gs

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