question ingition 123

[dario parra]

Good morning

Does anyone know the crankshaft and vacuum advance tables for the 123 ignition bt distributor? for an engine with twin carburettor m10

[Stevenc22]

If you have dual side draft carbs you might not have a vacuum pickup and so you will have to tune the car without the vacuum table.

 

This is my advance table for my dual DCOE 40 setup.

 

[TobyB]

Can the 123 use a throttle position sensor?

 

t

 

[ray_]

8 minutes ago, TobyB said:

Can the 123 use a throttle position sensor?

 

t

 

I think if you wrap one around the distributor cap clips, it may minimise the probability of the cap popping off. 

[TobyB]

Hmmm.  I use tie- wraps for that.  Maybe if I tie- wrap the throttle open?

 

t

 

[dario parra]

Thank you very much and what values do you have in the vacuum curve?

[Stevenola]

I have found it beneficial to bracket the desired idle rpm with the same advance amount.  For example, if you want to idle at 950 at 10 degrees, put the 10 degree point on an upper and lower range like 900 and 1000, this will prevent the advance from compensating by advancing or retarding based on slight fluctuations up and down in idle.  This elimintes "hunting" and results in a smoother idle.  Here is an example based on 1000 idle rpm and 15 degrees advance:

 

[dario parra]

Thank you very much and what values do you have in the vacuum curve?

[Stevenola]

31 minutes ago, dario parra said:

Thank you very much and what values do you have in the vacuum curve?

The vacuum curve is engine specific, you'd have to decide how much advance you want to add while not under load when cruising, for this check the distributor specs for your engine.  I have sidedrafts with vacuum ports but I am currently not running any vacuum MAP curve, I experimented with various curves but in reality I couldn't determined that they made any difference in mpg.  If you want to add a vacuum curve for say an additional 8 degrees advance, it would look something like this:

 

 

The advance kicks in at high vacuum/low load range of 21-79 kP.  What is critical to do is adjust the drop out values (in this example at 80 kP it removes the advance) so that you are not adding advance under load.  This can only be determined by driving your car and observing how much throttle it takes to get the vacuum to drop out when you mash the accelerator pedal, you want to get the advance to drop out (go to 0) before your engine goes into max load/low vacuum in order to avoid detonation.  The area from 80-100 kP represents full load/WOT.  In order to keep the vacuum advance from activating too early, I set the ignore MAP to 2500 rpm or so, this will make it available at cruising range and not mess with your accel from off-idle and low revs.  Final tweaking is done in top gear as this will be be when this is used the most, and you want to set it so it is not too sensitive to minor pedal changes at speed.

 

 

Edited August 15, 2023 by Stevenola

[dario parra]

Thank you very much