One cylinder idle - weird

Fingerscrossed

XS650 Enthusiast
Messages
48
Reaction score
30
Points
18
Location
Sydney, Australia
Hello all,

I may be doing something very dumb so I just want to check. The bike started idling on one cylinder suddenly, and I was also having carb issues.

I replaced the carbs with another set of BS38’s which have been cleaned (only carb cleaner + air compressor). The bike starts first kick and idles strong but still the left pipe is dead cold.

I changed spark plugs, caps, and leads. I put in a new set of points and re gapped, I also put in a new condenser, still one cylinder.

So it may be the coil, the strange thing is when I just switch over the leads (this is where I may be doing something wrong) the bike doesn’t start at all, and when I use the electric starter it’ll give a massive pop and sometimes a massive fireball…

I’ve attached a photo and video (although no fireball and maybe hard to hear). I’m assuming it’s not fuel, I also put a new coil in the right side (working side) but the left one looks relatively new (yellow and black wires). I tested with the multimeter and seemed fine, anyway, any help would be really appreciated!!

Start Pop
 

Attachments

  • IMG_7682.jpeg
    IMG_7682.jpeg
    359 KB · Views: 30
So it may be the coil, the strange thing is when I just switch over the leads (this is where I may be doing something wrong) the bike doesn’t start at all, and when I use the electric starter it’ll give a massive pop and sometimes a massive fireball…
On a points bike, you have to swap the lead to the points as well as the HT lead.
Points bikes are not wasted spark systems. They fire every two crank rotations... so if you just swap the HT lead, it'll be 180° out of time.
So just swap the leads coming out of the coil... grey and orange iirc and the HT lead. That will swap the coils as far as timing is concerned.
 
On a points bike, you have to swap the lead to the points as well as the HT lead.
Points bikes are not wasted spark systems. They fire every two crank rotations... so if you just swap the HT lead, it'll be 180° out of time.
So just swap the leads coming out of the coil... grey and orange iirc and the HT lead. That will swap the coils as far as timing is concerned.
Ah yes, thanks. Just tried this but it won’t start at all, hmm
 
Inspect Points I am thinking left is grounding
I would measure Voltage at Points . So the left is getting power
If not finding anything
When it runs on one cylinder Check if it is sparking on both the left and right at Points. Probably not since the pipe is cold. I would consider swap over all things right to left left to right
Coil condenser Spark plug + wire Se if the problem shifts side
 
Inspect Points I am thinking left is grounding
I would measure Voltage at Points . So the left is getting power
If not finding anything
When it runs on one cylinder Check if it is sparking on both the left and right at Points. Probably not since the pipe is cold. I would consider swap over all things right to left left to right
Coil condenser Spark plug + wire Se if the problem shifts side
Yes only the right side is sparking at points. I checked the spark against the engine, there’s a spark on the right side but not on the left (I switched plugs, wires and caps, still the same). I switched the coil wires and only the right coil is sparking. May just be a coil replacement? I’ll check again with the multimeter

Edit: just reread about points grounding. I’ll check that first
 
Yes only the right side is sparking at points. I checked the spark against the engine, there’s a spark on the right side but not on the left (I switched plugs, wires and caps, still the same). I switched the coil wires and only the right coil is sparking. May just be a coil replacement? I’ll check again with the multimeter

Edit: just reread about points grounding. I’ll check that first
Maybe my English is not good enough
If left points don't ground

I would shift the Coils physically left to right --right to left since a measurement cold without vibrations can show fine but under load it can be defect.
So the working coil right side is disconnected taken off and screws ( nuts ) taken off and at the same time servicing a bit cleaning scraping contact grease checking inside the wire connections. Then install to the left
And the left off serviced and installed to the right
 
Maybe my English is not good enough
If left points don't ground

I would shift the Coils physically left to right --right to left since a measurement cold without vibrations can show fine but under load it can be defect.
So the working coil right side is disconnected taken off and screws ( nuts ) taken off and at the same time servicing a bit cleaning scraping contact grease checking inside the wire connections. Then install to the left
And the left off serviced and installed to the right
I think you may be right. Just went to take the coil off and found this.. do you know where the other end is supposed to be attached?View attachment 258689
 

Attachments

  • IMG_7683.jpeg
    IMG_7683.jpeg
    340.1 KB · Views: 32
A quick and easy way to isolate the coil, HT lead and plug.... from the points and condenser:

Disconnect the lead from the coil to the points/condenser. Take a wire, needle nose pliers... whatever, and touch the coil spade (the one you took the terminal off of) and a convenient ground point... any bare metal. In other words, short that side of the coil to ground, then pull (unground) it. Tap it... tap tap tap. Every time you tap it, the plug should fire. If it does, the problem lies with the points, condenser or associated wiring.

If it doesn't spark, then the coil, HT lead (or cap) or plug is bad. Also need power to the coil.
 
A quick and easy way to isolate the coil, HT lead and plug.... from the points and condenser:

Disconnect the lead from the coil to the points/condenser. Take a wire, needle nose pliers... whatever, and touch the coil spade (the one you took the terminal off of) and a convenient ground point... any bare metal. In other words, short that side of the coil to ground, then pull (unground) it. Tap it... tap tap tap. Every time you tap it, the plug should fire. If it does, the problem lies with the points, condenser or associated wiring.

If it doesn't spark, then the coil, HT lead (or cap) or plug is bad. Also need power to the coil.
Ok great, I did that and it’s sparking on the right but not the left. I’ve already changed over the leads and caps so I don’t think it’s that.

The left coil is reading at 5, the right at 5.3, is that enough to be bad?
 
Ok, so then when checking the plug wire to the primary the right side reads 8.4, the left side reads 4.07. Could that be where it’s gone bad?
Well now we are talking a factor 2 .One side should be low Ohm and one High
Are any of these numbers on a different range on the meter 4 k ? And 8 k ?
That is significant

This is why the swap would be clearer I don't know what numbers they should have
 
Well now we are talking a factor 2 .One side should be low Ohm and one High
Are any of these numbers on a different range on the meter 4 k ? And 8 k ?
That is significant

This is why the swap would be clearer I don't know what numbers they should have
Yes that’s 4k and 8k, is there a reason the sides would be different? I don’t have any wires attached, they’re still on the mount but the ignition isn’t on or anything so they should be the same right?
 
Another update: there is spark on the left side (with good coil), none on the right. Switched leads and caps again, no change. Still not starting, popping and a bit of smoke. I’ll go pickup another coil and see what happens
 
If the coils are on the Workbench and one Measure 4 k and the other 8 k
performing the same measurements
It is methodologically sound to get the right same values on both at this stage in the Fault finding Process.

Can be other things but measured the same way both should have the same Resistance
 
Back
Top