Motorcycle Secondary Ignition Help (New to Using Scope)

Hello Everyone,
I'm hoping to get some insight on two secondary ignition waveforms from a 1987 Virago 535 XV motorcycle (V-twin), this is my first time using a scope ( Hantek 1008C).The bike does not run that well and seems to be misfiring from the front cylinder, I can see fuel misting out of the exhaust for the front cylinder also when I put my hand up to that exhaust pipe it seems to have more pressure coming out of it. I do not think it is a dead miss though (since both exhaust manifolds have the same temp when checking with a infrared temp gauge after running for a bit). I have checked compression and was in spec, also carb was rebuilt, that is why I'm leaning towards ignition issues. I recorded a video of each cylinder and it's waveform and uploaded them to YouTube. If anyone would share there insight on them It would be much appreciated!

Here are the links:

Front Cylinder:

Rear Cylinder:

Does the Virago have 1 or 2 coils?

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What are you scope settings ? That rear cylinder is missing the coil charge voltage ?

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Has 2 coils, 2kv/div, 2ms/div not sure if thats right for the settings (new scope user)

Time base looks ok how about your trigger?

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Not sure why but the waveform would only seem to stabilize if I set the trigger below the zero point, Otherwise it would just scroll across the screen. Maybe because I had the invert on? It was set at -1.98kv in this.

Your settings are OK the reason why the rear waveform is moving around on the X Time axis is the wave form voltage is unstable so you will cannot get a stable trigger. The coil charge (dwell) tiime is showing but is very long and off screen to the left

It looks to me like you have problems on both cylinders, the front cylinder looks like it has mechanical issue causing a major loss of compression pressure and the rear cylinder an issue with the coil/plug lead or plug.

I would do a primary and secondary ressistance check on both coils as it might confirm a coil problem but sometimes won't, and do a some kind of compression test or air pressure leak down test on both cylinders.

Your settings are OK the reason why the rear waveform is moving around on the X Time axis is the wave form voltage is unstable so you will cannot get a stable trigger. The coil charge (dwell) tiime is showing but is very long and off screen to the left

It looks to me like you have problems on both cylinders, the front cylinder looks like it has mechanical issue causing a major loss of compression pressure and the rear cylinder an issue with the coil/plug lead or plug.

I would do a primary and secondary ressistance check on both coils as it might confirm a coil problem but sometimes won't, and do a some kind of compression test or air pressure leak down test on both cylinders.

Valves probably have tightened up on that front cylinder with low compression. Nobody ever checks them since they take so long to go out of spec. When I was working in a dealer in AZ back around '99-'00, we had to check the valves on a new setup, and during the first service. Never saw a Honda or Yamaha that needed it ever on the first service. Sometimes with 30k miles they still didn't! A local guy has a FJR1300 that has 130k miles on it, and has only ever put gas, oil, and tires on the bike - that's it!

I seem to see tight valves on real old, or high mile bikes of that vintage. The engines were really well built. Even then it's rare. Never see cylinder/piston issues unless the machine was run out of oil.

You could try swapping the plug caps, and see if that ignition issue follows. Sometimes the resistors in there (if it has them) go bad and resistance goes through the roof. That'll show up on the secondary resistance test, or you can remove them and test them separately.

Yep, figured I'd see my fellow mmi grad smitty jump on this one. I have nothing to add

Smitty Smithsonite wrote: Valves probably have tightened up on that front cylinder with low compression. Nobody ever checks them since they take so long to go out of spec. When I was working in a dealer in AZ back around '99-'00, we had to check the valves on a new setup, and during the first service. Never saw a Honda or Yamaha that needed it ever on the first service. Sometimes with 30k miles they still didn't! A local guy has a FJR1300 that has 130k miles on it, and has only ever put gas, oil, and tires on the bike - that's it!

I seem to see tight valves on real old, or high mile bikes of that vintage. The engines were really well built. Even then it's rare. Never see cylinder/piston issues unless the machine was run out of oil.

You could try swapping the plug caps, and see if that ignition issue follows. Sometimes the resistors in there (if it has them) go bad and resistance goes through the roof. That'll show up on the secondary resistance test, or you can remove them and test them separately.

Valve clearance issues make sense, as looking at the rear cylinder wave form it looks a compression issue on the rear cylinder also in addition to ignition secondary (HT) issues.

I checked valve lash and was in spec, also compression was 160 psi.

Found ohm spec for coils on another forum stating that primary 4.2 (+-15%) and secondary is 13.2 (+-15%).

Heres what I had:

Rear cyl coil
Primary 4 ohms
Secondary 21.9k


Front cyl coil
Primary - 4.2ohms
Sec 21.6k

The waveform from rear cylinder is really screaming a secondary ignition problem, checking the ressistance of the coil and ht lead isn't a fool proof test so to me it looks like you have either have spark plug that has a cracked insulator inside the cylinder or coil or HT lead that is arcing to ground. A really mashed up waveform like the one from the rear cylinder can be really difficult to make sense of. There is a rule thumb that where the waveform looks wrong to the left of the red line in the screen capture you look for a problem external to the cylinder, but where the wave is abnormal to the right of the red line it is inside the cylinder.
My feeling is the coil secondary or HT wire insulation is breaking down but it could equally well be cracked spark plug, swap the coils and plugs between cylinders and do another couple of captures.

What is the view of the rest of the forum??????????????????????