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MG MGB Technical - 123 Ignition Question.
|Hello all. I have a 123 dizzy fitted to my 74 1/2 RB. I have it all set up as per instructions for my 847F engine (setting A,7 btdc). I have just started to use the car as my every day transport and have noticed that its running slightly hotter than i would like and also runs on a bit sometimes. I have a kenlowe fan fitted and even in cold weather i only have to stop for a very short time and the fan cuts in (is this normal?). The fan is set to cut in between normal and hot. The cooling system has been flushed and has a new radiater, hoses and thermostat. My question is. Can the 123 dizzy still be rotated to advance and retard the ignition? I have read the archives with interest and it appears with a 'normal' dizzy advancing or retarding the ignition 'could' solve my heating and running on problems. If i am able to make adjustments, what would you advise. Thanks in advance. Chris.|
|Yes you can rotate the dizzy to advance or retard the timing, the same as any other distributor. Try setting it to TDC and see how you get on. The engine running hot would say lean mixture to me more than anything else though.|
|As Ross says you can alter the timing with a 123 by rotating the body just like any other distributor. In fact you *must* retime the engine when fitting a 123, just like when changing points, fitting a pertronix trigger or anythng else.|
Retarded or over-advanced ignition - with any distributor - will cause hot-running and that will increase the likelyhood of running-on. Running-on is also affected by the grade of fuel used, if you use 'standard' 95 octane you will probably have to retard the ignition by a couple of degrees to prevent pinking. Pinking is likely to cause hot-spots which will cause running-on just like over-retarded timing. Earlier engines seem very susceptible to it.
Most people have the adjustable thermostat on after-market fans set much lower than the factory did on the later cars as they expect electric fans to keep the needle on N at all times. They may well on modern cars but that is because often the temp gauge is controlled from the ECU which deliberately filters out the 'normal' temperature fluctations to prevent owners getting paranoid. On MGBs it is quite normal to have the needle go up to around mid-way between N and H before the fan cuts in, and only bring it halfway back to the N before it cuts out again. If you have the fan switch set too low then depending on where it is located you can have the fan churning away blowing air through a cold radiator because the thermostat is doing its job.
|Paul Hunt 2|
|Hi, Ive read the archives and some say its best to set the timing at about 12 BTDC (although my engine should be 7 BTDC)because of different fuel octanes etc, and some say rotate the dizzy until the highest revs, then back off in stages until theres no pinking and leave as is. Is this the way to go. Thanks, Chris.|
|Chris Set the 123 as the instructions say for the advance curve you select. IE, with the timing mark lined up in the correct position (usually TDC) turn the dist.body so that the LED is visible, then lock up the clamp. Then when you start the engine the timing will be correct at idle (10*on most curves) and at all revs. Correct that is for the curve you have selected. You have not said what 123 dizy you have the GB4 or the MGgb4. If you are using the MG one Peter Burgess recommends #6 or #C The idea of the 123 is not to fiddle with spark advance but if your not happy try another curve. You should still use the timing light to check the accuracy of your settings. |
Denis is right, you have to check the advance settings, not because the 123 is wrong but human error. We always check for the max advance stated eg 30 degrees at 4000rpm or whatever. The 123 is easy to fit but must be fitted correctly to get the best from it.
We have fitted more than 10 and set up another 10 or so. We pick a curve then see what happens when we advance or retard it a little. Then we may try a different curve. The 123 is versatile especially the 123/GB-4-A-V.
|Whilst the book figure is a starting point it will depend on what fuel you are using as to what advance you can actually run. If you use 95 you will almost certainly have to back off 2 or 3 degrees to avoid pinking. With 97/98 you may well be able to run it at the book figures. *Always* use lack of pinking at any combination of revs, throttle opeing end engine load as the final arbiter of what advance you should be running.|
With something like the 123 you will be able to run it on *any* of the curves. Some will allow you to run more advance without pinking, and some less, it all depends how the curve relates to the characteristics of your engine. With all of the curves there is going to be part of the range where you could run more advance and so get better running, but that would cause pinking elsewhere in the range. Some curves will have more of this lost 'better running' than others, and even the recommended setting for your engines probably won't be ideal with todays fuels. The only way to get the best out the 123 is to determine on a rolling road what the ideal curve for youe engine and fuel would be, then find the curve that closest matches that. Short of that you might just as well use the recommended curve and set the timing for no pinking.
|Paul Hunt 2|
|Peter and others of coarse. Can you shed some light on which taco's do and do not work with the 123. Is there an easy fix? I asked this also on the MG exp forum and got good replies but I confuse easily.|
|The stock tach in my 1972 midget works fine with it, FWIW...|
|The MGB 73 and later tach which is voltage pulse triggered (black/white wire from the coil -ve to the tach input) will work with the 123 exactly as normal. The earlier current pulse type (loop of white wire from the ignition switch, via the tach pickup to the coil +ve) may work OK, although aftermarket electronic ignition systems often have problems driving this type correctly.|
|Paul Hunt 2|
I checked the timing yesterday with the intention of going through the the rev range as suggested, and found that the timing marks on the pulley 'bounce' about quite a bit. There is about a 5 degree movement (before and after) the TDC mark at 1000rpm. I've timed a few cars over the years and can't ever remember coming across this before. Is this normal for this engine, if not, what would be the cause. Thanks in advance, Chris.
|Any slop in the crank to distributor rotor path can cause this. Usually a worn distributor is blamed, but on my V8 it stopped (it never bothered me enough to do anything about it by itself) after I did a top-end overhaul with new cam chain and gears even though the distributor has probably done nearly 200k by now. Could also be wear in the teeth of the cam and distributor drive gear, and possibly clearance between the drive gear and the dog on the distributor. 5 degrees is a lot, if it didn't do it with the previous distributor then it looks like a problem wuth the 123.|
|Paul Hunt 2|
|Is your engine idling steadily?|
Yes, the engine idles steadily. In fact it sounds very sweet. Chris.
I adjusted the timing with the gun and although it run OK it didnt seem quite right. I put the 123 back as it was, but then realised that i had set it at TDC the first time i put it in, and it should have been 7 degrees BTDC as this is the static timing for the 847F engine. I also turned the rotor this time to get rid of any 'slack' and now there is very little movement in the timing marks (reading and understanding the insructions help!) Combined with the correct choke adjustment (another thread) the car starts and runs very well on choke and at normal temperature and the engine appears to run slightly cooler than before with no sign of pinking or running on. Thanks all for your interest and help. Chris.
|According to the leaflet I have - except for switch position 0 - all static timing is done at TDC.|
|When you set the 123 at TDC with the engine stationary you are not setting the timing to fire at TDC, just the light to come on. As soon as the engine is running and idling between 500 and 1000 rpm the timing is 10* BTDC. It does not fire in the position the LED shows. A bit different than other setups. |
Looks like i made a mistake with my static timing. I did check the technical data, but in the workshop manual, not the 123 instructions!!! (my wife often says i've lost it, but to be honest i dont think i ever had it to lose:-). Saying that i will leave as is for now, simply because the car is running slightly cooler and appears (so far) to run incredibly well, with no pinking or running on as it did at the TDC setting. May well have cured the problems by accident! Thanks for putting me right. hris.
|You have discovered a little known feature of these engines, that of some being able to run more advance than others even though they are all ostensibly to the same spec, and that is from new. The specifications for timing are come from two factors - firstly down to the basic design of the engine, and secondly a safety factor to cater for the variation in manufacturing tolerances in individual engines. This safety factor means that all engines can be adjusted to the same figure, and none (defects aside) will experience damaging pinking or detonation. Some engines will have a very small safety factory, and others a wide safety factor. I have had engines where I have been able to run several degrees more advance than the book figure without pinking (wide safety factor), and get a corresponding improvement in performance, cruising economy, and lower running temps. However my roadster is at the other end of the scale (low safety factor) where I have trouble on today's fuels even higher octane running at the book figure without pinking. The 123 uses strictly the book spec, and the timing light operating at TDC takes into account the book static figure of the curve you are using, to make life easier for the user i.e. not having to look up the figure for your distributor when setting static timing. You can move the 123 to get the best results for your engine and fuel just the same as you can adjust a mechanical distributor.|
|Paul Hunt 2|
This thread was discussed between 31/03/2008 and 14/04/2008
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