Britbike forum Forums British Motorcycle specific Brands Ariel forum Square four ignition total spark advance

Does anyone have any idea what rhe MK ll total spark advance is or a published advance curve by rpm ?Cant seem to find any information on this subject,as I have been building digital electronic distributors for vintage machines and have had this square four in my collection for a long time.now turning to its revival and adressing the ignition system.Fuel is next.
Mike

I seriously doubt that the exact range in degrees is critical.

Aye !!

Have a look at the distributor for it.
It may even be marked for the advance-retard range.
Or you could measure it.

Commando unit is marked as 12 degrees.
(So thats 24 degrees at the crankshaft).

Modern electronic units often have a totally different advance curve
than the old mechanical systems, and are often better for it.
Experiment ?

I agree,consistency is as important as the right advance at different rpm levels.Been building these for vintage indian 2 cyl Scouts,Chiefs and the modern curves work amazingly well as this module has 8 curves from 24 begrees to 35.After all its a 4 stroke air compressor add air fuel and spark.Balance that and
the fuel gives great performance.
Mike

I'll look through my info and see if the advance is listed. There are UK solid state upgrades- their literature may also help.

Here's distributor advance specs for a 1956-59 MK2 Squariel. This is from a Lucas Equipment and Spare Parts book. If yours is an earlier year, the advance range is the same back to '52-'53 but the distributor part number changes. Hope this helps.
Model: DKX4A
Part #: 40486A
Supercession #: 40426
Advance range: 14-16 degrees.