LCGB Forums

why does it fluctuate? strobe on tickover at about 14-15 degrees then move to about 19 degrees when rev'd.

Cheers Steve

Talk to Anthony Tambs (Scootronics) on Face Book, he's the ignition guru.

also helpful if you said what make stator, flywheel, cdi, etc.....

well, not really sure. Indian flywheel I assume and not sure of stator origin. but why would "static move?

Stevepshipley wrote:well, not really sure. Indian flywheel I assume and not sure of stator origin. but why would "static move?

Yes they do wander a bit but as I mentioned, Anthony Tambs is the man to explain it.

It will naturally retard. In other words, the piston will be higher up the bore when the spark occurs with increasing revs.
This is because the the time taken for the electronics to trigger is a constant and the speed of the piston is a variable as you rev it.
Other things such as slight wear in the mag bearing can also have a minor affect here.

ok, so will it be ok peaking between 17-19 degrees under high revs and significantly lower than that at low revs/tickover?

Static timing can even advance with revs (!) but this is rare and normally due to misalignment of the pickup and triggers on flywheel. I had this recently and I was shocked how much the static (meant to be) timing could wander. Not an issue if it retards a few degrees with revs but not good when it advances as it'll cause the motor to run hotter.

Adam_Winstone wrote:Static timing can even advance with revs (!) but this is rare and normally due to misalignment of the pickup and triggers on flywheel. I had this recently and I was shocked how much the static (meant to be) timing could wander. Not an issue if it retards a few degrees with revs but not good when it advances as it'll cause the motor to run hotter.

Auto Advancing on magneto driven Cdi's is largely due to the wide degree of difference in spark voltage from tick over to full chat. About 3:1 on a Lammy. The higher spark voltages will conduct across the plug a smigeon earlier.
DC driven CDI's spit out the same spark voltage whatever the revs.

A quality programmable CDi module has a compensation table/graph that you need to determine values for first to remove these electro-mechanical variances. The engine then runs to a perfect static timing setting. From there, you add in your required timing graph. Ten, what you strobe at the flywheel, should emulate exactly what you have on your software graph.

The cheap ones dont have this compensation graph and so you have to make appropriate allowances in the main timing graph.

I have an Anthony Tambs stator on one scooter and a cheap Indian stator on the other.Both run with Indian flywheels.I've set both at 17 degrees BTDC and when strobed they're both rock steady throughout the rev range.

Also having too big a plug gap won't help.
As won't using a resistive plug with a resistive plug cap.

Fast n Furious wrote:Also having too big a plug gap won't help.
As won't using a resistive plug with a resistive plug cap.

That’s interesting, my Gamma definitely shows the engines running hotter using a resistor plug than it does with a standard one, so the resistor somehow advances the ignition slightly then?

I suspect there may be other criteria that may cause that. Hard to say really.