123 distributor setting

[Doctor slow]

hope for some more help from the grown-ups.

I ave a 123 ignition distributor (the one with 16 set programs), and have been trying to get to grips with the advance curves that they have programmed in. I haven't been able to find much data for the best advance curve for a GT6. the best I have found seems to be:

RPM           Advance degrees (crankshaft)

500             12

1000           16

1600           21

2000           23

2600           28

3000           30 (max advance)

does this look reasonable?

None of the settings according to the limited data that 123 supply gives a max advance of 30 degrees, or anywhere near 23 degrees at 2000rpm. However, i've found another site which shows different data, with setting 7 giving 22 degrees at 2000 rpm , and max 30 degrees at 4500 rpm. I'm reluctant to try this if 30 degrees is too much advance. I've tried three other settings and the engine seems to lack power, especially at around 2000rpm under load. If it had a "normal distributor, the symptoms seem like  sticking bob-weights.On a reasonably steep hill, i'm in third gear. Without load it revs reasonably freely, but certainly isn't smooth (although it does have a fast road camshaft). I'm pretty sure that the carburettors are set properly.

Any ideas would be welcome.

[Pete Lewis]

28/30 deg is around the max mechanical advance of the std distributor at 3000rpm   more revs does not give any more advance 

the triumph dizzy test data is in the workshop manuals , and double check the data you have as most often dizzy test data is decelerating from max  not building up to it 

Pete

[Nick Jones]

The numbers above look reasonable.

Are you factoring in that in addition to the degrees the distributor adds, you will also need the basic static advance. That is, the static advance, nothing added by the distributor and likely to be very close to low speed idle advance with the vacuum disconnected, wants to be something like 10 to 12 degrees. The 123 then adds to that according to the curve you select and the total is your timing number.

I’m struggling to find good data on the available curves - sure I’ve seen graphical representations in the past but can’t see any now. From the tables I’ve found, a static/idle setting of 10 deg and curve 7 looks closest.

What static/idle setting  do you have? Do you have a strobe? One way to do it is work backwards from the high rpm setting and set that to 30 deg at 4500. You should make this check anyway as going much above 30 deg at high rpm and wide open throttle risks severe engine damage.

The 123 instructions are not great.

Nick

 

[Nigel Clark]

Here's the WSM advance curve for GT6 Mk3.

When I fitted an Aldon Amethyst programmable ignition to my GT6, it was set up on the Aldon rolling road and the optimum was very close to the most advanced figures from the ranges quoted in the WSM. That's for a standard engine with the 18/58 58/18 cam.

Nigel

 

[Doctor slow]

Thanks for all this help. I've set the static timing to 10 degrees BTDC. The 123 data for setting 7 is max advance 20 degrees at 4500 rpm, so I presume that the figure of 30 degrees that I found (above)is including the static. Anyway,  setting 7seems to be safe, so I'll give that a try. I've spoken with a couple of people now, with this 123 distributor, and they both said that they just used trial and error, one setting at a time. I would have liked  to apply a bit of science to it, but the data supplied by 123 is just not great.

[Nick Jones]

Looks like Nigel's WSM information needs to have the static setting added on also.

The information supplied by 123 is really not good enough.  I also don't think that any of the 16 available curves is a very good match for the factory GT6/Vit Mk2 curve as that is actually quite aggressive and tips a fair amount of advance in quite early on both mechanically and via vacuum.  This does mean that you are less likely to get mid-range pinking issues, but at the cost of some mid-rpm torque and fuel economy.

Using curve 7 you could try increasing static to 12ºBTDC at idle.  That should take you to 24º total @ 2000 and 32º total @ 4500 and might brighten things up a little.  I'd advise against going beyond that as the total advance beyond 32º at high rpm/full throttle is too much.

A bit late now but I think the 123-tune is worth the extra as it gives much more flexibility.   I've not used one myself, but we do have 3D mappable distributorless ignition on my Vitesse (and on son's 1300 Spit), which gives superb accuracy and control flexibility.  The 123-Tune gets about 80% of the way there and is much easier to fit.

Nick

 

 

 

[John Harris]

On a switchable 123 ignition you time it at TDC, the green light comes on, and therefore the curve given in the instructions is already the total advance.  When you have installed the 123 then re-time it with a programable strobe at say 23 degrees at 2000rpm, as per the choice of curve, it will be more accurate than static with the green light at TDC.

I run a 1500 spitfire with a programable 123 and have found that it will take more than the max set out in the WSM. I developed my curve from a mapped ignition system published on the internet and then adapted it. My 1500 is standard with K&N air filters, yellow carb springs and slightly richer needles for the K&Ns, original engine, 75000 miles.

I attach it for comparison.

 

 

 

 

[Doctor slow]

Reawakening of this topic, please. I'm having trouble getting my head around the vacuum advance. As bought, my car had the two carbs linked with  a balance tube where the rocker breather, according to the diagrams, should be connected and the rocker breather venting to atmosphere.  I've replaced this with the "correct" arrangement, with the rocker cover breather connected to the two carbs. Now when trying to set the advance curve, the vacuum advance doesn't seem to make any difference. It would appear that the rear carb "breather intake tube" is adjacent to the vacuum tube on the carb body. By connecting the breather, am I losing any vacuum from the carb. I haven't stripped out the carb to see if there is a connection between theses two tubes, but they are very close. Any thoughts and advice gratefully received.

[NonMember]

The vacuum advance pipe should be just the other side of the throttle butterfly, which makes a big difference at light load! The breather feeds into the "constant depression" chamber, which never achieves much vacuum but isn't at atmospheric either.

[Pete Lewis]

there is a small 6mm tube fitted in one  carb fixing flange as rob says just behind the throttle plate

this has no connection to manifold vacuum , the dizzy vac is generated inside the carb as air flows past the throttle disc and gives most vac at a partial(cruising) throttle 

so the vac generated rises as throttle open  where as manifold vac is high at idle and nil  at full throttle..........  both   very different 

dizzy vac is a economy device to advance timing  during driving , supposed to gain aprox 4 mpg it has no effect on performance most advantage is when cruising 

pete

[Doctor slow]

Thanks for all that. will leave the breather alone then. Continuing struggle with the 123. Seriously thinking about a "normal " distributor (but not with points!)

[Pete Lewis]

its my waffle but there are a lot of Must Haves  you dont want 

Pete