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MG Midget and Sprite Technical - Ignition timing 'wobble'

I just decided to check the ignition timing on my 1330 A-series midget. I was surprised at how much the timing appeared to fluctuate (I set the idle speed at a steady 1500 rpm). The timing seemed to wobble back and forth. It's hard to say by how much but I would not be surprised if it was as much as +/- 5 degrees if not more.

As I have a 123 electronic dizzy, a new cam and dizzy drive (well, only 2000ish miles so not expecting any wear) I was puzzled by this amount of inexactitude in the timing. Is this 'normal'? I can't see this as a 'good thing' but I can't see how to eliminate it either.

Chris
Chris Hasluck

Does the 123 use vacuum advance ? could there be a split in the pipe ?
Do you still get the wonder at higher revs where the mech advance should be 'all in' maybe around 4000 ? Does the 123 use mech advance ?
I used to get this happening with my points setup, but once i changed to a simonbbc module it improved dramatically.
Andy Phillips (frankenfrog)

Hi Andy

There is no mechanical advance with a 123 - purely electronic. Your point about the vacuum advance might be worth exploring. I'll try that later today.

I'll also check what is happening at higher revs.

Chris
Chris Hasluck

Make sure you use a hard plastic vacume tube...I found on my truck that the softer vacume hose (old aged) can collapse under vacume, and then once vac is released it springs back into shape

I think orginally the 1st midgets had a copper line from the manifold to the dissy advance

We just discussed this a couple/few months back and paul (walbron??) From OZ had some great insight into this ...its worth a dive into the arcives....just dont eat an hour before entering that 5 legged abyss

Prop
Prop and the Blackhole Midget

I noticed this with my 123 when I set it up with the strobe some years ago on my 1500.
I used the "mean" position of the spread and it has worked fine since.
JB Anderson

Set the timing at 4500-5000 to that specified.(vac disconnected) Vac advance doesn't usually work till 1500rpm plus on the 123s.

Peter
Peter Burgess Tuning

I was not asking about how to set the timing and I am aware of the method of setting the timing by running up to 4500-5000 revs (set mine to 30 degrees at that) but my initial post refers to the variation at low revs. I am surprised by the amount of wobble and just wondered if that was normal. I had expected that with electronic dizzy there would be little wobble. Just curious - the car seems to run OK in any case.
Chris Hasluck

Hi Chris

I was trying to say (in a round about way)don't worry about low speed just make sure set at high rpms then low speed takes care of itself.

We get flutter no matter what system is fitted at low revs,pulses in chain, gears, skew gears, cylinders firing.......

Peter
Peter Burgess Tuning

Glad to hear, Peter and Chris. Sounds like it may be normal. I just got through checking my timing this morning - 1275, pertronix, vac. D/C, timing 30* @3000 rpm and the timing mark fluttered around maybe +/- 2.5* at steady (as steady as I could hold it) rpm. Bottom line is the car is running pretty well.
Jack Orkin

I suppose you are aware that these triggers suffer from 'electronic' noise when using strobes.I had lots of scatter with my Pertronix till the RR guys told me to dump the copper leads and use encapsulated double silicon HT leads instead. Once changed the reading went to rock steady.
Fergus Pollock

This thread was discussed between 28/10/2014 and 01/11/2014

MG Midget and Sprite Technical index

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