It shouldn't. If the advance is stopped by anything other than the vacuum unit it will likely tilt the points and therefore change the dwell. The dwell shouldn't change more than say 1 degree with the vacuum advance.
I see thanks
How should I wire up the electronic dizzy without the coil ?
I measured my BAU1962 some days ago but with the coil in the circuit
The lead which normally goes to the coil negative gets connected like a points distributor. You then need to connect the power wire to a positive supply which could be built into the machine or even just a 9v battery. The negative of the supply gets connected to the distributor body.
I connected exactly like this but it does not work. The LED is good, because it works with a normal dizzy.
It should be like my very "basic" diagram ?
Maybe I discard the LED function from the machine and I will use a regular strobe for timing and my multimeter for Dwell measure
powerspark-powerspark-electronic-ignition-kit-for-lucas-35d-distributor-k3_24v__52995.jpg
I doubt your distributor would like that very much. The output you have here hard connected to the +12V. Given that it switches to Earth it may well damage the module.
My suggestion earlier for using a resistor in place of the coil is twofold;-
Firstly, with a Coil, it stores energy sorta like a capacitor, however on opening the charging supply, unless it has a moderate load, it will produce a high voltage spike of a few hundred volts. I doubt the LED would like that and it's likely why the LEDs are going to god.
Secondly, on the points or module opening and thus 'firing' the coil, the charge in it doesn't disappear right away but decays over time, only millisecond, but none the less, it's not instant. If the LED survives the initial spike, the coil discharge time will keep the LED illuminated, thus totally distorting the true dwell period as observed.
I suggested a 2.0 Ohm Resistor as many coils for use with electronic modules seem to be 1.5 ohms and some at 0,8 ohms, (though I think some too are 3.0 ohms, so you may need to check here). Without getting too hung up on how such coils behave in an ignition circuit, from a testing perspective (with your machine) what's important is that you don't exceed the current that the module will withstand. With a 2.0 ohm resistor that's around 6 amps (and that's pretty much inline with a coil). Passing more current through it than it's rated for will usually damage the module. If it's rated for a 1.5 ohm coil, and you use a 2 ohm resistor on it, that will pass less than it's maximum rating and so will survive happily.
Respectfully, I did read 68/86's suggestion of a Ballast Resistor, these are usually anywhere from 0.8 to 2.5 ohms but only have a ~ 15 - 20 watt rating. Just running the sums on that, at 0.8 ohms, that's 15 amps and 180 watts and at 2.5 ohms, that's 4.8 amps and (near enough) 60 watts, so it wouldn't be suitable, though you maybe able to use a higher resistance type for short periods as in realty, it's not being continuously connected.
In normal use a Ballast Resistor don't have a full 12 volts across it, but is used in series with the coil to drop the voltage at the coil to around 9 volts. This is usually done to aid with starting, when the Ballast Resistor is by passed and so a full 12 volts is presented to the coil instead of the running voltage of 9 volts. So, there's only around 3 volts across the Ballast, and so the actual wattage of them need be way less than if it was the full 12 volts
