Spark plug shorting method for carb sync with EME digital ignition system

[Enforced_Leo44]

Hi everyone,

Just got my hands on a EuroMotoElectrics digital ignition system, I'm going to install it tomorrow, my original Bean Can is having problem with sticking advance weights, tried cleaning it but didn't help, so I wanted to swap out to a more definitive solution.

Anyways, the question I wanted to ask is: can I still use the spark plug shorting method to sync my carbs with this ignition system? I read on their site that it's definitely not recommended to run the engine with one spark plug disconnected because it might damage the ECU and sensor, does that also apply if I short a plug?
As per my thinking, it shouldn't be an issue since the electrical current still has "somewhere to go", but then again, better to be safe than sorry

[gspd]

Answer to your question: If the HT wire is grounded, or connected to a grounded spark plug, you won’t harm the ignition.

For the record, the shorting method is not the best way to set up your carbs, but if it works for you, go for it.

[Rob Frankham]

I would be very reluctant to use plug shorting on any electronic ignition. With the plug lead shorted, there is a very intense and much higher current through the plug lead. This in turn means that the current in the primary of the coil will be higher and that the reverse EMF thorugh the coil could generate voltage spikes high enough to damage not just the EMU but also any other sensitive electronic equipment. Always short through a grounded spark plug (or emulator) if you must use shorting to balance but, I agree with gspd, it's not the best way to balance carbs.

It's also worth bearing in mind that most electronic setups can produce a dangerously high voltage... be careful out there...

Rob

[barryh]

I would certainly not short the plug leads on electronic ignition although I've done it on points ignition including with my kit built ignition amplifier in place after noting that there are several blocking diodes in the electronic circuit to protect against a back emf and there is a condenser to absorb the back emf as well.

It's worth explaining why I judged that to be safe.

The coil will have a fixed amount of energy in Joules that get dissipated regardless of whether there is a spark gap or a dead short. The HT current that creates will depend on the HT voltage which will rise until it creates a spark across the plug gap. If it's a dead short instead of a gap then voltage doesn't get to rise as much and so the HT current will be many times greater than normal. Simple ohms law.

On proper electronic ignition with coils of low primary resistance the joules stored in the coil will be at least 4 times greater than for points coils making the HT current at least 4 times higher on a dead short so there is much more potential to do damage.

[Rob Frankham]

I would certainly not short the plug leads on electronic ignition although I've done it on points ignition including with my kit built ignition amplifier in place after noting that there are several blocking diodes in the electronic circuit to protect against a back emf and there is a condenser to absorb the back emf as well.

It's worth explaining why I judged that to be safe.

The coil will have a fixed amount of energy in Joules that get dissipated regardless of whether there is a spark gap or a dead short. The HT current that creates will depend on the HT voltage which will rise until it creates a spark across the plug gap. If it's a dead short instead of a gap then voltage doesn't get to rise as much and so the HT current will be many times greater than normal. Simple ohms law.

On proper electronic ignition with coils of low primary resistance the joules stored in the coil will be at least 4 times greater than for points coils making the HT current at least 4 times higher on a dead short so there is much more potential to do damage.

Great description, thank you.

Rob

[gspd]

On proper electronic ignition with coils of low primary resistance the joules stored in the coil will be at least 4 times greater than for points coils making the HT current at least 4 times higher on a dead short so there is much more potential to do damage.

Hmmm..Your point seems a valid but..
Is a dead short worse than a totally fouled plug? I've never personally seen a fouled plug screw up an ignition system.
Anyway, what do I know? I grew up getting electrocuted by lawn mowers and minibikes that had a (factory installed) springy metal lever that I would have to press up against the spark plug tip with my bare finger to turn the damned things off. Didn't always work as intended, especially when raining. All the yung'uns these days have been spoiled with handlebar mounted kill switches.

[barryh]

Hmmm..Your point seems a valid but..
Is a dead short worse than a totally fouled plug?

Good point, a dead short is not worse than a fouled plug as an open circuit will cause the coil to generate it's highest possible HT voltage which stresses the coil insulation and may lead to damage on electronic ignitions. There does seem to be a consensus on not pulling a HT lead off to disable one cylinder when electronic ignition is fitted. The shorting method has to safer than that.

There's no getting away from the fact that shorting will increase the HT current many times and while I've used the shorting method on my points booster electronic ignition without any adverse effects it does retain the original points coils which limits the energy being dissipated.

I suppose there is a difference between risking my own kit built points booster which cost all of £10 and advising someone else to risk their fancy aftermarket electronic ignition which may have cost $$$.

[Rob Frankham]

There's no getting away from the fact that shorting will increase the HT current many times and while I've used the shorting method on my points booster electronic ignition without any adverse effects it does retain the original points coils which limits the energy being dissipated.

Not knowing the details of your points booster, I can't really comment but, if it's essentially substituting a semiconductor switch for the points (no matter how triggered)... as you say, the energy dissipated in the igniton system is dependant on the coils rather than the switching method so your system using the original coils probably doesn't greatly increase the energy being produced.

Rob

[barryh]

Not knowing the details of your points booster, I can't really comment but, if it's essentially substituting a semiconductor switch for the points (no matter how triggered)... as you say, the energy dissipated in the igniton system is dependant on the coils rather than the switching method so your system using the original coils probably doesn't greatly increase the energy being produced.

Rob

A little less energy because unlike the points contacts there is always going to be a fractional voltage drop across the collector-emitter on the TIP162 power transistor. It was measurable too as I checked average primary current before and after installation and it was fractionally lower.

velleman.JPG (34.71 KiB) Viewed 352 times

[Rob Frankham]

Not knowing the details of your points booster, I can't really comment but, if it's essentially substituting a semiconductor switch for the points (no matter how triggered)... as you say, the energy dissipated in the igniton system is dependant on the coils rather than the switching method so your system using the original coils probably doesn't greatly increase the energy being produced.

Rob

A little less energy because unlike the points contacts there is always going to be a fractional voltage drop across the collector-emitter on the TIP162 power transistor. It was measurable too as I checked average primary current before and after installation and it was fractionally lower.


velleman.JPG

In general, a transistorised system like this will switch more quickly and cleanly than points so, if you are losing energy due to the forward bias of the transistor, you are probably making up for it.

Rob