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MG Midget and Sprite Technical - Megajolt question- timing light

I'm fitting a Megajolt and am using a timing light with dial in advance. I gather that the EDIS system uses a wasted spark technique and thus produces two sparks per cycle instead of one. So to check an advance of 10 degrees (limp home timing) do I dial in 5 degrees or twenty degrees? Any advice from Megajolt users would be welcome. I'm guessing on 5 degrees but need comfirmation.

Steve
Steve Church

Steve - you are getting two sparks per cycle on each lead (hence the wasted spark) so you need to half it...


Make sure that you get the missing tooth as close as possible and that there is no chance of the sensor moving under load or vibration...just dont ask how I know ;-)

Toby Anscombe

Toby, thanks for that. I'm still messing about with getting the bracket right. I had the pulley machined but am having to grind the 'dips' deeper so the sensor can better differentiate between teeth and 'dips'. Having some trouble getting a stable timing mark. Another evenings work with the dremel should get the pulley sorted.
Steve Church

I'm confused by this...could you explain

Are you talking about the difference between crank degrees and cam (ie distributor) degrees....that is to say that the dissie runs at 1/2 crank speed? so 10deg BTDC is '5deg' at the distributor

being wasted spark set up won't change the ignition timing...will it?
robnrrugby

You get an extra flash on the exhaust stroke - so it will flash when the mark is 180deg out of phase with the TDC pointer as well as in the normal position, but on the ingnition stroke, it appears normal - so you shouldnt have to change the timing you dial. 5deg is still 5deg. No?
Nick

I have experience of Emerald 'wasted spark' system, but not Megajolt. As Nick says, the basic timing is the same as a car on points...

A
Anthony

~so it will flash when the mark is 180deg out of phase with the TDC pointer~

Sorry to be a pedant but if you are talking about looking at the pointer to the crank pulley with a wasted spark system, the flash is every 360 degrees of crank rotation isn't it?

i.e. if it is timed at 10BTDC on the compression stroke then the wasted spark flashes at 10BTDC on the exhaust stroke.

I agree though that the timing of the ignition event relative to the piston remains the same between crank or cam triggered ignition systems.
robnrrugby

For a standard non adjustable timing light I would agree that 10 degrees is 10 degrees. But the settable timing light measures the time between sparks to know when to fire the light. As there are now two sparks per cycle instead of one the timing light will get its calculations wrong by a factor of two. So for a ten degree setting on the light it will divide 180 degrees by 36 (not 360 degrees by 36) and fire at 5 degrees BTDC. So for it to time correctly to ten degrees it should be set to 20? Err..is this right? Do you follow?
Steve Church

I have just resolved my confusion, having googled timing light + ignition advance

I wasn't aware that timing lights existed that would show advance...and not having needed to buy a timing light light for the last 20 years that particular development had completely passed me by! I'm there now, 5 deg of advance on the strobe would be equal to 10 degrees in the crank if you're using wasted spark, and your timing light....which I think is what you said in your first post.
Many thanks
robnrrugby

Steve what setup do you have? TPS or MAP?

has anyone got a good ignition table to share?
danny

Steve, did you buy a toothed timing wheel outright or get yours done?
Tarquin

a easy way to do the wheel is when you harvest the edis bits is to get the pully off a siera 2ltr twincam the toothed wheel is a press fit on the pulley and the od is identical to a midget pulley.
danny

Danny, I have a MAP setup. Not installed the controller yet, just the EDIS stuff. Having problems getting stable timing (jumps around a bit.
Tarquin, I had the pulley machined when I had the engine out last winter. If I had to do it again I would probably get a recess turned into the pulley to accept a trigger wheel. Not sure how welding would affect the rubber in the pulley though. I have just spent several hours deepening the teeth profile with a Dremel as I dont think they were deep enough.
I shall put the controller into the system this weekend to see if I can get more stable timing.

I think Toby may be able to help with some ignition maps (he says hopefully)
Steve Church

chaps I am not at home but I have a source for trigger wheels...

Can maybe help out with maps just need to know the spec & compression

The slots on a pulley. Need to be 5mm deep to really work and the sensor needs to be 1mm away with no runout.

On phone so hence no real text content
Toby Anscombe

This thread was discussed between 20/07/2008 and 22/07/2008

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