123 ignition

[Stephen Aitken]

Hi

Just looking to get some thoughts. I have a supercharged engine and recently purchased a 123 ignition with Bluetooth. I’m having a lot of issues getting the car to start.
I’ve checked plugs for spark - ok and fuel pressure/delivery is good, the carb has been checked for float height, damper oil etc and battery is fully charged. Have checked TDC and rotor is pointing to no. 1 plug - have confirmed it’s on the squeeze and not blow. The diz cap is also fine. There is a green light you can see once diz cap is off and this needs to be just on per the 123 instructions (assuming building a bit of advance). The curve I’ve programmed is per other similar supercharged engines..
I’ve sort of hit a brick wall with this today - the car does splutter a little as if just about to come to life but never does. I’ve turned the diz a little CW and CCW but not any nearer. I was thinking I need to maybe put it a little degrees BTDC to start but not according to the instructions as it should be built into the curve I have.

Any help much appreciated
Thanks
Stephen

[Vic Butler]

Presumably all was ok before the 123 was fitted.. I had one on my Land Rover a few years ago, worse than useless. The engine was down on power despite being set up exactly as in the instructions and then a regular misfire occurred. I returned it as requested by the supplier, they "lost" it and I got a full refund.
The original distributor with Charles Kettering's antiquated ignition system was fitted and full power was restored.
I've no faith in any of these fully electronic distributors. I've just got Pertronix on the Land Rover and Lumenition Optronic on the MG, with both distributors having been completely rebuilt by the Distributor Doctor.
The fault is obviously in the 123. A spark plug with a spark outside the cylinder might not necessarily work when in the cylinder.

[David Witham]

It may not help in this case, but with starting problems it is worth checking how many volts the coil is receiving with the ignition key in the running position and then with the key in the cranking position. I don't know if it is a problem with replacement ignition switches, but I have often found much lower volts in the cranking position due to higher resistance.

[Charles Farran]

Hi,
I appreciate that my comments don't help Stephen , but Vic, i have nothing but praise for the 123 ignition fitted to my standard & original 1800 MGB about 9 years ago. (It was not the more recent version that you can adjust for road use & then on the track). It has been totally reliable & all i have done is renewed the rotor arm & cap as once i hadn't ensured one of the clips that hold the cap on wasn't seated correctly. No messing about with poor points & fiddling to ensure they open & shut at the correct time etc. etc. (I know there are purists who insist that an original distributor & points is the only way to go , but i still have the original set up as a back up)! Other than the colour of the cap , the 123 set up looks original with no exterior modules.
Cheers
Charles

[Vic Butler]

The lack of power after I fitted the 123 to the Land Rover was likely down to a lack of mechanical advance as the low compression engine (8:1) needs more advance than a higher compression engine.
A misfire developed though and I got my money back after I returned it to the supplier and they "lost it!"

[Michael Barclay]

Hello Stephen
Could the problem be with the voltage being supplied to the 123 Ignition? Your car would originally have been fitted with a 6 Volt ignition system using a 6 volt coil and a ballast resistor built into the loom. This resistor is bypassed when the starter motor is engaged to provide 12 volts to the coil for starting then drops back to 6 volts under normal running. I am sure the 123 needs 12 volts to operate correctly so it could be it you need to bypass the ballast resistor and fit a 12 volt coil.
Best regards
Mike Barclay

[Vic Butler]

It's only the coil that the ballast resistor circuit affects. Surely the distributor has its separate 12 volt supply. The Lumenition Optronic on my B takes its 12v supply from an ignition controlled source on the fuse box. The voltage to the coil doesn't, or shouldn't, affect the distributor.
A conventional distributor is connected to the coil only by the earth lead to the points and the king ht lead.
Of course, Hall Effect electronic ignition systems like Lumenition Magnetronic or Pertronix don't need a power supply.

[Paul Hollingworth]

I helped my friend fit a 123 distributor to his mildly tuned MGB.(his engine is closest to a 1972 18V engine and has the larger inlet valves) He's tickled pink with it. We set it to curve 2 which is the 40897 advance curve standard for pre 1973 cars. Peter Burgess says in his book that this curve is suitable for all but the highest state of tune. It had previously had an unsuitable 45D 41610 curve. My friend is going to Peter for a rolling road tune up in November. It will be interesting to see what he thinks of how we set it up. (Strobe 20 deg btdc @1000 rpm vac disconnected)

[Michael Barclay]

Hi Vic
The 123 installation manual shows connecting the red 12 volt feed from the distributor to the positive terminal of the coil. If you follow this instruction on a rubber bumper car the distributor will only be supplied with 6 volts. As you suggest a separate 12v feed from the fuse box will be required. i would suggest checking the voltage on the red distributor wire to ensure it is 12 volts.

[Charles Farran]

Vic,Michael,
The instructions supplied with my 123 which is a type 123\MG-4-R-V for MG-A & MG-B (6 or 12 Volt;negative earth only).
The red wire is connected to the + of the coil & therefore other than on cranking operates as it is designed to do with a ballasted system on 6 Volts.
The tech data says the 123 is designed to operate on a range 4 - 15.0 Volts.
Charles