4000 rpm limit 123 distributor

[Tom W]

Hi Grant,

Thanks, this helps. Your graph looks a spot on assessment of the situation, although I don’t understand why the figures on the 123 advance curve don’t match what the dashboard with the dials shows. Is there anywhere in the software where you input a static timing number?

The advance figures shown on the images with the dials will be the total advance the distributor is applying, i.e. a combination of both mechanical and vacuum advance. Having said that, I think your vacuum advance curve is wrong, so you won’t actually be getting any vacuum advance. It looks like it only applies any advance under positive pressure, which you won’t get on a naturally aspirated engine.

You can remove the risk of the vacuum advance clouding the picture by removing the vacuum pipe and plugging it so you don’t get an air leak.

What we still don’t know for sure is whether there’s any static advance applied due to how the distributor has been installed. The rolling road report would suggest there is though, having measured 8 degrees at idle.

Whether you’re on the red or the green line, both are too far advanced at higher revs. For a standard engine, you should follow the factory curve as Christopher said.

[christopher storey]

Right, I think we are beginning to see daylight. The bluetooth ( I presume that's what the dials are ) show that

1. You have too much total advance - it should not exceed 29 degs at any point

2. In the 1000 to 3000 rpm band, your curve rises insufficiently steeply, so that you have insufficient advance at these points

I suggest that as a starting point you should aim for a curve as closely matching the factory curve as you can get - the line you have drawn for the factory curve is ideal

In all these things it is best to remember that, as a general principle, a few degrees of retard will not matter much, but even a few degrees of over-advance can be very harmful . Detonation cannot always be heard as pinking, particularly at higher rpm, but can burn holes in pistons in a very short time if it occurs continuously

Sorry if I'm teaching my grandmother , etc. etc

PS Apologies to you and to Tom - I see that I have just more or less repeated what he has just said

[Tom W]

No apology necessary, Christopher, your explanation is clearer and more succinct than mine.

I think the thing we still don’t know, though, is where the distributor is set to. The dials show the total advance based on where the 123 thinks TDC is. If the distributor is set with some static advance, the dials would still be out compared to the timing marks. Putting a timing light on at idle would confirm if there’s 0 degrees, 8 degrees or something else, at least relative to the pointer.

[Grant]

Hi Tom and Christopher,

Thank you again for your replies ,
So it seems my plan should be to get it to zero advance at tdc and then see what it says ?
And maybe try to change the setting to match the factory .
I did not realise I was at risk of doing damage as she is running so well in the other gears .
I will read through again what you have said and
I will try put it to zero and then let you know what the 123 says ,

Thank you

Grant

[Tom W]

That sounds like a good plan.

Until you confirm what you’re set to, particularly at the top end, I wouldn’t risk driving it, and certainly not putting it under heavy load with large throttle openings.

[Grant]

Yeah thanks Tom

[Gfhug]

And a new set of UM needles?

Geoff

[Grant]

Hi Geoff ,
Thank you for your reply,
Yes I may have a fuel issue as well, but I’m going to try and sort this 123 situation before I Chang e anything else, off to do battle in the garage,

Thanks
Grant

[mgcjag]

Hi All...just realised i posted the wrong photo (map)n previous post above....have just edited it......also regarding the 123 tune worth noting that a friend recently had a problem with the dashbiard app.....the revs showing on the guages of the app were reading 500rpm less than the actual revs of the engine...so beware....Steve

[Grant]

Ok Steve ,

Thank you

[Tom W]

Looking at Steve’s revised photo, the vacuum advance now makes more sense. 100kpa is atmospheric pressure, so values below that represent manifold vacuum. You’ll be getting up to 10 degrees additional advance under certain vacuum conditions, which you’ll experience when revving the engine on the drive.

You need to remove vacuum advance from the equation for now, so disconnect the pipe, and plug the end so you don’t get an air leak into the manifold. With the vacuum disconnected, you should find what the red line on your graph, and the black line actually match.

You also need to draw another line on your graph, which is the black line, but shifted up by 8 degrees. This is what I think you actually have for mechanical advance, so still too advanced at the top end.

[mgcjag]

Something else to note after chatting to a friend who has set up 3 123 tune dizzys....the rotor arms on the ones he set up do no sit in the position that you would expect with a standard dizzy(and drawings in the service manual) so your spark plug leads will need to be positioned to suit.....Steve

[Grant]

Hi Guys and thank you for sticking with me !

Tom , am I still setting the static at 0 ( which Ive just done ) or do it need to put that back ,?

I did not have a big enough socket to turn the damper so I've moved the dizzy anti clock wise to get it at 0 on the timing light is that ok ?

just having a coffee and pop master then going to figure a way of blocking the vacuum

thanks

Grant

[christopher storey]

Don't worry too much about the vacuum tube, the volume of the leak from them is minimal. If you really want to block it, a matchstick will do!

[Grant]

ok Christopher , thank you , Im off to give it a go ,

thank you

[Grant]

HI Christopher/Tom
do I need to block the carb as well or just the dizzy hole ?

I presumably do not want to suck air into the carb that way ?
just remove it both ends and block both ?


thank you

Grant

[rswaffie]

Hi,
Apologies if I’ve missed something, but how are you ensuring that no1 cylinder is at tdc on compression stroke if you can’t turn the engine over by hand? I know that setup instructions vary depending on the type of 123 you have, but getting the initial static timing position correct before rotating the 123 to get the green light is important.

[Tom W]

There’s 2 ways to set the 123 to TDC.

First is to rotate the engine by hand until the pointer on the crank pulley points at the TDC mark. This needs to be TDC on the compression stroke of cylinder 1. You can find this by removing a spark plug, and putting your finger over the spark plug hole as you rotate the engine. You’ll feel the compression on the compression stroke but not the exhaust stroke. This probably needs an assistant, and obviously needs a means of turning the crank. If you don’t have a big socket, you might get away with a pry bar wedged against the front pulley bolts. When you have the engine at TDC, you then follow the 123 instructions to get the light to light up. From there, set the advance you actually want at idle (8degrees) in the software.

The other way, as your engine runs, is to set it dynamically. Start the engine, and check what the idle timing is with a timing light. It is probably 8 degrees, but the 123 is not applying anything at that point, as the value for idle in the curve is 0. So it’s only 8 degrees because of where the distributor is set to. Rotate the distributor anti-clockwise until the timing shows 0 degrees. The engine will run worse as you do this, but then you’ll know the values you see on the 123 dashboard represent what the timing at the crank actually is. Once you’ve got it to 0, when the 123 curve is also at zero for idle speed, set the idle timing in the software to the 8 degrees you want it to be.

[Tom W]

You only need to block the hole to the carb. A match into the open end of the flexi pipe will work. Don’t poke anything into the distributor, as you might damage the pressure sender. As Christopher says, the air leak is minimal so won’t make much difference, and you won’t be driving the car like this.

[Grant]

Hi All

ok we are getting somewhere!:-)
I have disconnected the vacuum pipe from the carb and it is now running as per THIER original table or as near as dammit, and she does not continue to rise and rise (degrees advance) like she originally did.
.
500 0
1000 0
1400 7
2300 14.6
3500 23.4
4500 28

This is with the static at 0 and the vacuum off.
Do I leave it at 0?
Do I leave the vacuum off ?
obviously I have not driven it yet but should I take her for a spin, before trying to adjust anything?

Grant