New Member, with an electrical problem

romainnorberg

romainnorberg

Joined
Nov 1, 2025
Messages
4
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Hi all,

Hope you're well.

I bought my Norton Commando 750 at the end of last year, I did an oil change and a complete carburetor overhaul at the beginning of this year. I haven't ridden much, just a few tests to make adjustments. I also checked/adjusted the valve clearances.

The motorcycle is equipped with a Boyer Bransden Micro-MK4, and the current battery is a Shido LTX7A-BS. I have very little history on this machine, but externally it is in very good condition. According to the seller, it was fully restored 10 years ago and had only about 20km at the time of purchase.

Last week I went for a slightly longer ride and started some kind of power issues.

The symptoms are as follows:

- The right exhaust is cold and flooded with gasoline (the spark plug is also wet)
- (Without the air filter) gasoline is being spit out of the right carburetor
- The battery voltage is unstable while the engine is running: between 3 and 7 volts (~13 volts with the engine off)

Initial tests:

- By swapping the coil wires: same problem, no combustion on the right side
- By swapping the coil wires AND the spark plugs: combustion is fine on the right side but not on the left.
- By putting another spark plug on the right side (still with the coil reversed): again, no combustion problem on the right side.

In short, something quite unstable...

During my last tests, I then disconnected the black module (approximately 2x2cm) which can be seen in the photo. Both cylinders are firing properly (hot right exhaust and visible exhaust gases) and the battery voltage is approximately 13 volts (not charging I thing).

I initially ordered a Yuasa YTX14AHL-BS battery; I'd already encountered this issue on another motorcycle, and it was the solution I hope.

However, can anyone tell me what the black module (approximately 2x2cm, photo IMG_7065.jpeg) is? Is it part of the ignition kit?

Thanks in advance for your answers.

Romain (from Belgium)

Photos: https://drive.google.com/drive/folders/1DbZHZgVD0Horxb_wHrmADZVyC0zUmM3Q?usp=sharing (I don't know how to embed the photos directly into the post)
 
Check the fuse, not just check the fuse but also the fuse holder looking inside at the soldered ends that contact the fuse, they can make intermittent contact which would give very odd V readings.

Your Boyer is wasted spark, both plugs fire twice every 720 degrees, one in a live fuel filled cylinder and the wasted one in the exhausting cylinder. The Boyer box works with both plugs or fails with both plugs. The exceptions are bad leads, plugs, coils which will fail on one side.

One very rare but one issue that can get a Boyer to only spark one plug is a compromised earth path from engine back to the positive terminal of the battery. Its a quick and easy test, run a wire directly from the head back to the battery positive terminal and then see if the left fires up. Modern spark plugs can foul at the drop of a hat so have a few new ones to hand, iridium seem to be less prone to fouling.
 
romainnorberg said:
The symptoms are as follows:

- The right exhaust is cold and flooded with gasoline (the spark plug is also wet)
- (Without the air filter) gasoline is being spit out of the right carburetor
- The battery voltage is unstable while the engine is running: between 3 and 7 volts (~13 volts with the engine off)

Initial tests:

- By swapping the coil wires: same problem, no combustion on the right side
- By swapping the coil wires AND the spark plugs: combustion is fine on the right side but not on the left.
- By putting another spark plug on the right side (still with the coil reversed): again, no combustion problem on the right side.
Click to expand...


Is there any typos here or am I not understanding something?

Reading the last two sentences,,,, To me it reads as if you replaced the spark plug on the side that was working but did not replace the spark plug on the side that was NOT firing???

I guess it depends on the meaning of "no combustion problem on the right side". Does this means that that was no trouble on the right side then? Or that there was no combustion on the right side?

I quite often read too much into these things.
 
TJBaker57 said:
Is there any typos here or am I not understanding something?

Reading the last two sentences,,,, To me it reads as if you replaced the spark plug on the side that was working but did not replace the spark plug on the side that was NOT firing???

I guess it depends on the meaning of "no combustion problem on the right side". Does this means that that was no trouble on the right side then? Or that there was no combustion on the right side?

I quite often read too much into these things.
Click to expand...
Right side is cold and flooded, ie not firing.
 
TJBaker57 said:
Is there any typos here or am I not understanding something?

Reading the last two sentences,,,, To me it reads as if you replaced the spark plug on the side that was working but did not replace the spark plug on the side that was NOT firing???

I guess it depends on the meaning of "no combustion problem on the right side". Does this means that that was no trouble on the right side then? Or that there was no combustion on the right side?

I quite often read too much into these things.
Click to expand...
You're absolutely right, he swapped the faulty plug over to the left and the right started working OK. Then he replaced the plug on the right and it made no difference. He should have replaced the faulty plug that is now on the left.
 
kommando said:
Check the fuse, not just check the fuse but also the fuse holder looking inside at the soldered ends that contact the fuse, they can make intermittent contact which would give very odd V readings.

Your Boyer is wasted spark, both plugs fire twice every 720 degrees, one in a live fuel filled cylinder and the wasted one in the exhausting cylinder. The Boyer box works with both plugs or fails with both plugs. The exceptions are bad leads, plugs, coils which will fail on one side.

One very rare but one issue that can get a Boyer to only spark one plug is a compromised earth path from engine back to the positive terminal of the battery. Its a quick and easy test, run a wire directly from the head back to the battery positive terminal and then see if the left fires up. Modern spark plugs can foul at the drop of a hat so have a few new ones to hand, iridium seem to be less prone to fouling.
Click to expand...
Thank you for the explanation. I checked the fuse but not the connections. I will carry out the tests you recommended.
 
TJBaker57 said:
Is there any typos here or am I not understanding something?

Reading the last two sentences,,,, To me it reads as if you replaced the spark plug on the side that was working but did not replace the spark plug on the side that was NOT firing???

I guess it depends on the meaning of "no combustion problem on the right side". Does this means that that was no trouble on the right side then? Or that there was no combustion on the right side?

I quite often read too much into these things.
Click to expand...
Sorry, you're right, I made a mistake in what I wrote last time. It was indeed the left-hand spark plug that I replaced (with a new one), the one where there was no longer a spark. But that didn't change anything. I also tested with two other new spark plugs (Champion N7YC and NGK BP7ES).
 
Do you have no combustion OR no spark? If you have spark and also a stuck float or needle, resulting in a completely flooded cylinder, you probably won't have combustion.
 
romainnorberg said:
Hi all,

Hope you're well.

I bought my Norton Commando 750 at the end of last year, I did an oil change and a complete carburetor overhaul at the beginning of this year. I haven't ridden much, just a few tests to make adjustments. I also checked/adjusted the valve clearances.

The motorcycle is equipped with a Boyer Bransden Micro-MK4, and the current battery is a Shido LTX7A-BS. I have very little history on this machine, but externally it is in very good condition. According to the seller, it was fully restored 10 years ago and had only about 20km at the time of purchase.

Last week I went for a slightly longer ride and started some kind of power issues.

The symptoms are as follows:

- The right exhaust is cold and flooded with gasoline (the spark plug is also wet)
- (Without the air filter) gasoline is being spit out of the right carburetor
- The battery voltage is unstable while the engine is running: between 3 and 7 volts (~13 volts with the engine off)

Initial tests:

- By swapping the coil wires: same problem, no combustion on the right side
- By swapping the coil wires AND the spark plugs: combustion is fine on the right side but not on the left.
- By putting another spark plug on the right side (still with the coil reversed): again, no combustion problem on the right side.

In short, something quite unstable...

During my last tests, I then disconnected the black module (approximately 2x2cm) which can be seen in the photo. Both cylinders are firing properly (hot right exhaust and visible exhaust gases) and the battery voltage is approximately 13 volts (not charging I thing).

I initially ordered a Yuasa YTX14AHL-BS battery; I'd already encountered this issue on another motorcycle, and it was the solution I hope.

However, can anyone tell me what the black module (approximately 2x2cm, photo IMG_7065.jpeg) is? Is it part of the ignition kit?

Thanks in advance for your answers.

Romain (from Belgium)

Photos: https://drive.google.com/drive/folders/1DbZHZgVD0Horxb_wHrmADZVyC0zUmM3Q?usp=sharing (I don't know how to embed the photos directly into the post)
Click to expand...
Have a look at where the wires connect at the unit under the timing cover, the factory crimps are terrible, one of mine just slid out. VIP. membership will let you upload direct.
You might need to get a new regulator, get that voltage sorted out.
 
Last edited:
Yakatak said:
Do you have no combustion OR no spark? If you have spark and also a stuck float or needle, resulting in a completely flooded cylinder, you probably won't have combustion.
Click to expand...
I have a spark, but it doesn't seem stable. It sometimes backfires, but the exhaust stays cold and the carburetor is spitting out fuel.

I'll receive the new battery in a few days; I'll keep you posted.

Thanks for your replies.
 
romainnorberg said:
(I don't know how to embed the photos directly into the post)
Click to expand...
Go to more actions (extreme right) then 'share' and copy the link. That's not the original position for the flasher relay and it would not usually fit into the clip that way but probably fitted due to it's location next to the battery, I assume the flashers/direction indicators were added later as I doubt your model would have had them originally?


 
I think bikes sold in Germany had to have indicators didn’t they ?

I assume they’d be fitted by the dealer or importer if the factory didn’t ?
 
It looks like a *'1971' model although it seems to have some later parts on it so it could be a later model rebuilt with some earlier and later parts. The rectifier is also not in the usual position for that period.

*I was going by the 930/68 and /69 carbs and 30/30 manifolds.
 
Last edited:

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