Ignition - wasted spark?

[pptom]

Sorry for the simple question!
Is my standard points ignition on my 250 wasted spark or just once firing per 4 strokes?
Got a lead on a red scitsu, but they list singles in the red or white models.
Tom

[themoudie]

Aye Tom,
Reading through this UK site link for Scitsu:

Code: Select all

http://www.scitsu.co.uk/docs/fitment.htm

The important difference appears to be whether your ignition is timed from the crankshaft or the camshaft.

Might I suggest that you remove your spark plug and find TDC on the compression stroke, then turn the engine over slowly, using the rear wheel and a high gear engaged and note when the points open and how many revolutions of the engine have been made.

Speak with Scitsu directly and others whom may post on this site and currently use a Scitsu instrument. It is your machine and only by observing your machine will you be certain of its operation.

I hope this helps give you confidence to look and enquire directly of the supplier (AJS Motorcycles).

My regards, Bill

[Rick]

There's a 2/1 gear ratio between the crankshaft and the contact breaker 'camshaft'- 2 crankshaft revolutions per 1 contact breaker revolution. The 4 strokes of the engine take place in 2 crankshaft revolutions, so you'll get 1 spark per 2 crankshaft revolutions- no wasted spark.
If the tachometer is driven by the ignition coil you'll want an instrument that read 2X the ignition frequency- if you have a crankshaft pickup you'll want an instrument that reads 1X.
Unless, of course, I'm wrong.
Rick

[pptom]

Thanks chaps, the engine is stripped and not at my house at the minute, hence the question.
I needed a quick answer so posted on here instead of going to scitsu, knowing that a lot of you are in the states and are watching this while I'm several hours ahead and in bed!
Great info Rick, so it's definitely the 'white' one I need, showing 1/2 a spark per engine revolution.
Tom

[LaceyDucati]

Hi'
White backed Scitsu tacho's are used for original points, Lucas Rita and any ignitions with a single pickup or trigger mounted in the points housing. All running at 1/2 engine speed, with no wasted spark.

Red back tacho's are for any crank triggered ignitions like MZB and Electrex self generating. Also electronic systems like Sasche, Boyer, Lucas hall effect etc, which have dual pickups, magnets or slots which although running at half engine speed still have a "wasted spark.

You can return units to be re configured as white or red, but the cost including post begins to eat into the cost of a new unit.

Nigel

[Jordan]

Annoying they don't just provide a selectable input, like often seen on car aftermarket tachos.