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MG MGB Technical - 123 ignition

Hallo, I want to put a 123 ingnition in my MGB GT 1973
With a motor 18V F-H 3770 what is the best curve to use.and the static timing point???
The motor was originaly used in a MORRIS MARINA
rww remy

Hi,

I and others in the local MG Club have put 123s in their cars.
I was recommended and now use the generic British 123 (123 GB 4RV, from memory) rather than the MG version, as it gives a better choice of curves.
On my 18GB engine I am running curve B, which seems OK, no pinging or other untoward behaviour. Another guy uses curve C without problems. I haven't tried C yet so can't comment.

Timing is done by setting the distributor LED to just turn on at the crank set to TDC. The electronics in the 123 give a zero advance to 500 rpm then 10 deg to 1000 rpm, then whatever the curve.

Full information and a useful forum at
http://www.123ignition.nl/

Herb
Herb Adler

Hi again,

One thing I forgot to mention is the tacho connections.
If you have a RVI, ie current sensing, type then you need to leave the white wire on the coil, but do not connect the red wire from the 123 to this. Connect it to the bunch of white wires near the firewall, which are direct switched by the ignition switch.

Herb
Herb Adler

The current sensing tach finished in 72, changing from RVI to RVC (on the faceplate if you are not sure) for 1973.
Paul Hunt 2010

Paul I looked at the faceplate and it is RVC. Can I let the wire BW going to the tach in paralel with the black wire from the 123 on the - side of the coil, and the red wire from 123 on the + side of the coil
Thanks for info from everyone, grt
rww remy

Yes, the only difference between the 123 and standard distributor for a chrome bumper with RVC tach is the additional red wire that goes to the white wire on the coil which should be the +ve.
Paul Hunt 2010

Rww,

The F part of your engine number indicates that your engine was originally from the Marina TC. It was probably fitted originally with a Lucas 41032 distributor which corresponds to 123 curve 8.
The single carburettor Marina and some MGBs with 18V engines'were fitted with Lucas 41234 distributors which corresponds to curve 9.

It might be worth trying both curve 8 and curve 9.

My 1972 B has a non original 18V engine and I use curve 9.

Ref: Notes from MGCC MGB Register Workshop Nov 2004.

Regards,
David.
D M B LEGGEAT

Hallo David, thanks for your info, this is correct,my motor is Morris Marina TC with the original distributor, where can I see the number of the distributor ???
The static timing is -10 now
REMY
rww remy

The distributor reference number was usually stamped on the outside with the designation i.e. 25D5, 45D5 etc. The original curves are really only relevant with the original fuels, todays are very different so a different curve may well give better results. So much so that one supplier of the 123 recommends MGBs use the generic version and not the MGB version as Herb has said. But whether you would tell the difference short of a rolling road is another matter.
Paul Hunt 2010

Remy,

41032, 41234, etc are all types of 25D4 distributors.
The 41032 number should be stamped on the main circular body of the distributor below the square casting that holds the vacuum advance module and vernier adjust screw.

You may need to experiment with different curves for the reasons Paul mentions.

I use 98 octane petrol in my B.

Regards,
David.
D M B LEGGEAT

Hallo dear helpers I hope this is my last question before I put the 123 distributor.
The instalation instructions say:
Turn fhe engine with the Lucas distributor until the static timing point is indicated on the pulley, this is now -io° but if I see on the technical data delivered with the 123 for an 18v motor it is TDC and not -10°
My question where must I set the static timing point on TDC or -10° before mounting the 123 distributor.
Thanks for help
Remy

rww remy

Hi Remy,

This confused me some too, but eventually someone resolved it for me.

To time the dizzy, set the crank to TDC on #1. What the instructions, re the old dizzy mean, is that by setting the dizzy to the #1 firing point you actually have the #1 firing point and not #4. If you remove the old dizzy before doing this you will find it hard to determine if your TDC is for #1 or #4.
Once you have determined that #1 is near TDC on its firing stroke, carefully set the crank to exactly TDC, by the timing mark.
Now install the 123 dizzy and follow the instructions.

The Lucas info means that the static timing point for the Lucas dizzy is 10* BTDC. The 123 will give this advance internally, so you do not need to set it 10* advance, but at TDC.

Herb
Herb Adler

Yes, all 123s are set for static timing by the internal light at TDC for simplicity, the electronics then give the correct advance for running according to how the switch is set.
Paul Hunt 2010

This thread was discussed between 17/03/2010 and 30/03/2010

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