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Posted by Bucko
- September 06, 2021, 13:23:07 PMQuote from: Troll on September 06, 2021, 08:13:44 AMNot sure your description is accurate or perhaps I'm misunderstanding it. On these bikes, one coil feeds a pair of plugs on one cylinder, the other coil feeds a pair of plugs on the other cylinder. The coils are triggered by timed (i.e. offset) pick-ups from the crank via the ECU. Not sure if they fire every revolution or not (the ECU may prevent this - but I doubt it), but if they do, then both coils fire on both the compression stroke and the exhaust stroke (hence the 'wasted' spark). The energy from both the compression spark and the wasted exhaust spark is the same - it doesn't matter which stroke it's onI posted this a while ago, when the topic first came up, but it disappeared. 1500s have 2 dual coils, one for each plug on each cylinder. They are waste spark. The bulk of the spark energy goes to the cylinder with fuel in it. The fuel near the electrodes of the plug ionizes and provides a path to ground for the electric charge from the coil. The other cylinder has exhaust gases in it, and they don't provide much of a path, so the spark is quite weak (waste spark) Since there are 2 plugs per cylinder, the same setup is used in tandem. 800s have one coil per cylinder, and they are single tower. They are "single fire".
The motorcycle 'Ground' is not used for firing the plugs in the same way as a single fire coil which fires from coil to ground. On a dual fire system the motor is just part of high voltage conduction path - it's not a 'ground' relative to the coil output. On dual output coils, the energy travels from the (+) side of the coil output down the high voltage lead, through one plug (anode to cathode), through the motor, through the other plug (cathode to anode) and back up the second plug high voltage lead to the (-) side of the coil output. I may have 'anode' and 'cathode' direction swapped - the point is: energy flows one way in one plug and the opposite way in the second plug to complete the high voltage circuit.
Posted by Troll
- September 06, 2021, 08:13:44 AMI posted this a while ago, when the topic first came up, but it disappeared. 1500s have 2 dual coils, one for each plug on each cylinder. They are waste spark. The bulk of the spark energy goes to the cylinder with fuel in it. The fuel near the electrodes of the plug ionizes and provides a path to ground for the electric charge from the coil. The other cylinder has exhaust gases in it, and they don't provide much of a path, so the spark is quite weak (waste spark) Since there are 2 plugs per cylinder, the same setup is used in tandem. 800s have one coil per cylinder, and they are single tower. They are "single fire". I installed a true single fire system on my hotrod SuperGlide decades ago. Required 2 pick up coils and two dual tower coils. I was running two plugs per cylinder, and each coil serviced one cylinder. Here's what that looked like:
Posted by tj
- September 06, 2021, 07:34:45 AMQuote from: Bucko on September 05, 2021, 00:06:47 AMThis is exactly the way I understand it.So, in the case of a twin-plug V-twin, both plugs in the same cylinder (on the same coil output) fire at the same time. Since the two plugs from one coil complete the high voltage circuit - they both fire with equal 'energy'.
I'm pretty sure both plugs (in a cylinder) fire for both the compression stroke and the exhaust stoke (i.e. both plugs fire a 'wasted' spark).
Posted by Bucko
- September 05, 2021, 00:06:47 AMQuote from: chief on September 04, 2021, 22:49:23 PMSo, in the case of a twin-plug V-twin, both plugs in the same cylinder (on the same coil output) fire at the same time. Since the two plugs from one coil complete the high voltage circuit - they both fire with equal 'energy'.Dual fire shoots spark to both cylinders at the same time from an single coil. Most of the spark goes to the cylinder under compression while a smaller bit go to the exhaust stroke. There is some "wasted spark" as a result.
I'm pretty sure both plugs (in a cylinder) fire for both the compression stroke and the exhaust stoke (i.e. both plugs fire a 'wasted' spark).
Posted by chief
- September 04, 2021, 22:49:23 PMQuote from: Bucko on September 04, 2021, 20:53:24 PMWhen you mention 'dual fire', is that the same as: 'wasted spark' (like on inline 2, 4, or 6 cylinder bikes)? If ignition is triggered by crank position sensors, which I think they are, then it's likely a wasted spark, no?
Dual fire shoots spark to both cylinders at the same time from an single coil. Most of the spark goes to the cylinder under compression while a smaller bit go to the exhaust stroke. There is some "wasted spark" as a result.
Posted by Bucko
- September 04, 2021, 20:53:24 PMWhen you mention 'dual fire', is that the same as: 'wasted spark' (like on inline 2, 4, or 6 cylinder bikes)? If ignition is triggered by crank position sensors, which I think they are, then it's likely a wasted spark, no?
Posted by chief
- September 03, 2021, 18:02:06 PMOpening up this topic for discussion.
Considering the age and differences of our Drifters (1500 and 800) - do our bikes have single or dual fire ignitions? Both the same? Different on 800 and 1500?
If you know the answer(s) post your info here, references if you have them.