New Member, with an electrical problem

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)

romainnorberg said:

However, can anyone tell me what the black module (approximately 2x2cm, photo IMG_7065.jpeg) is?

Click to expand...

Not exactly black but that's the flasher relay.

romainnorberg said:

Is it part of the ignition kit?

Click to expand...

No.

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.