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DCOEs & Distributors

Nick Farrow

Donation Time
What do you guys with DCOEs do about the distributor with refernce to the fact that it's not very easy to connect up a line to the vacuum advance? Can you have the 25D4s bob weights changed so it has a suitable curve and can work without vacuum, or do you source a 23D4 and change the bob weights in that....or do you go for a more expensive solution and get an electronic distributor? I'm getting close to putting my DCOEs on my car and I haven't come up with a solution for this problem yet....

Cheers
Nick
 

TheBrownHornet

Donation Time
Hi Nick,

On mine the vacuum advance has been removed and I rely solely on the mechanical advance. This was done by the previous owner so I'm not sure the details. If you believe all the speculation, the vacuum advance plate is often sited as a weak link leading to inaccurate spark timing so at the expense of economy people remove it and lock the vacuum advance plate down.

I'm looking into ways to put it back and I've seen a guy with a lotus elan come up with a nice simple solution. The Weber DCOE's have a "vacuum take off port" above each throat. You can remove the bung and fit a vacuum tube. Connect the four together and you have your vacuum advance signal. I don't have my Weber tuning manual with me, but have a look at the exploded diagram and it shouldn't be too hard to find.

Cheers

Graham

Better just ad a caveat: The Weber manual refers to the 152 carbs so I don't know if these exist on old carbs. Mine are 40DCOE72 and 73 and they have them.

Here's a link to the Webcon site with the exploded diagram. Part #48 is the "Vacuum Take Off Cover"
http://www.webcon.co.uk/weber/40dcoe.htm
 

alpine_64

Donation Time
Nick,

i would ditch the lucas dizzy and go with a Bosch full electronic unit with mechanical advance. They are well priced for what they are and far superior to anything lucas put out.. also no more points!
 

Alpine 1789

SAOCA President
Diamond Level Sponsor
I am sure Michael's advice is the best way to go, but just so you know your options, I put a Lucas 43D4 Distributor (with a Pertronix) on my car when I was running the DCOEs. That is the distributor that Rootes used on the H120 and it was also used on a bunch of cars, including MGBs and Midgets between 1975 and 1980. While I never got my DCOEs right, I don't think the distributor had any bearing on the problems. (I am now convinced that the problem was with my manifold, not the carbs and will one day try them again with a better manifold.)

I never got around to putting the stock dizzy back on the car when I put the 32/36 back on and have been running with it ever since.
 

Nick Farrow

Donation Time
Thanks for the info guys! I was thinking about using either a 23D4 or 43D4 but they're not the easiest things to get hold of, and of course it's likely the advance curve will need changing. I've also be looking at distributors from these people:

http://www.123ignition.nl/

I'm not sure if they're available outside of Europe so you may not have seen them, but they seem quite good - fully electronic with several different advance curves built in.

Michael, what kind of Bosch distributor are you using? I've also got a couple of questions to ask you about your Weber setup as I've been studying your photos on Weshots...but I'll save that for another time!

Cheers
Nick
 

alpine_64

Donation Time
Nick,

I am runnign a Bosch scorcher electronic igntion with meachanical advance. As for weber questions feel free to PM me and ill give you my email..
 

RootesRacer

Donation Time
Something for you all to consider, unless you have a specifically built or have and application of dizzy (like perhaps an actual holbay), none of the above dizzys are going to be appropriate for running DCOEs with full mech advance.

Basically you need a lower mechanical full advance angle, which gets there faster than stock. Then you set your static timing with more idle advance getting to a final timing of about 32 to 34 degrees.

To do this you need to replace or modify the advance weights (to limit full advance stop) and put in slightly lighter springs than stock.

The 25D alpine dizzy (most years) have 26 degree stops (marked 13), which is too much timing change without vacuum advance to help with light load advance.

HTH
 

serIIalpine

Donation Time
What I would like to know is: How much timing from the mechanical is correct?
26 degrees is too much well how much is enough/correct?

Also: How heavy a set of springs do I need? The ones I have are to heavy I know but has anyone sourced a set from another dist. or bought a set at the hardware store that were perfect.

This is something I've wanted to do for some time but no one seems to have these particular answers.

Eric

'62 SerII
 

RootesRacer

Donation Time
What I would like to know is: How much timing from the mechanical is correct?
26 degrees is too much well how much is enough/correct?

Also: How heavy a set of springs do I need? The ones I have are to heavy I know but has anyone sourced a set from another dist. or bought a set at the hardware store that were perfect.

This is something I've wanted to do for some time but no one seems to have these particular answers.

Eric

'62 SerII

Excellent questions Eric, but different engines need different timing figures
to make peak power without detonation.

This is not something you can just drop some parts into it and drive off.
Those parts do not exist, so you have to make/modify what you have, and in the case of the springs, find something that works.

On the weights, there is a section of metal that becomes the max advance stop, this will need to be built up with metal (welded or brazed) and then machined down by trial and error using a distributor machine and a strobe.
You could also do this on your car, but its more work.

For a hot alpine like most of us have (higher compression webers and a cam), static timing would need to be around 16 to 20 degrees, max timing would need to be 32 to 34 degrees, so the max mech advance will be in the range of
14 to 18 degrees, the more compression the less mech advance needed.
The springs set the advance rate, which is pretty simple.

You could take your dizzy to a recurve specialist but they tend to think they know what timing you need, and they cannot possibly know that.
If you do make sure YOU specify what timing you want, and they will see if they can do it. Then you MUST verify on your car that they did what you asked them.

When using a dizzy with stock advance rates (set for vacuum advance), you can set your max advance in the 32 to 34 range, but your idle and light throttle timing will be rather retarded and you leave fuel economy and mid range power on the table.
 

alpineclive

Diamond Level Sponsor
Did you ever buy the 123 Ignition ?

Hi Nick

I have a Holbay engined Harrington with 40 DCOES, Holbay cam, head and pistons and I recently bought a 123 Distributor (w/o Vacuum advance) and wondered if you had done the same. If so what setting have you found to be most effective?

Thanks in advance
Clive

Thanks for the info guys! I was thinking about using either a 23D4 or 43D4 but they're not the easiest things to get hold of, and of course it's likely the advance curve will need changing. I've also be looking at distributors from these people:

http://www.123ignition.nl/

I'm not sure if they're available outside of Europe so you may not have seen them, but they seem quite good - fully electronic with several different advance curves built in.

Michael, what kind of Bosch distributor are you using? I've also got a couple of questions to ask you about your Weber setup as I've been studying your photos on Weshots...but I'll save that for another time!

Cheers
Nick
 

RootesRacer

Donation Time
I'd be concerned about the advance curve in the 123 distributor.

They sell it as a general purpose distributor but most every engine out there has a different curve so how does that work?

Most applications that run DCOEs and no vacuum advance have 10 to 15 degrees advance where most stock distributors are 18 to 26 degrees.

Running such a distributor with webers will typically leave you under advanced at lower RPMs.
 

alpineclive

Diamond Level Sponsor
123 Distributor

Hi RootesRacer

Thanks for your message ..I imagine I have a lot of learning to do on this subject ..here goes :). According to the installation guide there are sixteen switchable settings, 0 thru F, each of which has different characteristics at 500 to 1000 rpm, 2000 rpm and then the third number is a t the rpm indicated

Curve degr. advance degr.advance max.degrees
(switch setting) @500-1000 rpm* @ 2000 rpm* advance@rpm*

0 10,0 15,0 27,0@4200
1 10,0 16,5 27,0@3600
2 10,0 19,0 27,0@3000
3 10,0 21,0 27,0@2400
4 10,0 16,0 30,0@4500
5 10,0 18,0 30,0@4500
6 10,0 20,0 30,0@4500
7 10,0 22,0 30,0@4500
8 10,0 17,0 33,0@4500
9 10,0 19,0 33,0@4500
A 10,0 21,0 33,0@4500
B 10,0 23,0 33,0@4500
C 10,0 17,5 36,0@4500
D 10,0 20,0 36,0@4500
E 10,0 22,0 36,0@4500
F 10,0 24,0 36,0@4500


If I understand it correctly, once I got the engine running I used my strobe to set the timing to approx 12 deg BTDC, however, that must mean I should add +2 to every setting above because the 123 has a 10 deg BTDC setup as default (?). I have used several settings but settled on C for the moment. I guess that means I am at approx 12 deg BTDC at 1000 rpm, 19.5 at 2000 rpm, 38 deg at 4500 rpm.

Really appreciate any help anyone can give.

Best regards
Clive
 

RootesRacer

Donation Time
The rootes engine isnt going to want more than 34 degrees at 3000+ RPM.

You probably are going to want to have 18 to 20 degrees at idle, and 32 to 34 at the RPM where the max advance occurs.

This would be 14 or so total advance degrees.

None of those setting yeild this, so I guess choose the closest which to me looks like #2.
 

Ken Ellis

Donation Time
Clive,
I think I saw one of the products on that site has an option to switch to a secondary "curve" based on sending 12v on a control wire. If there's one setting that's good for low rpm, and another for high, then you could experiment with the selection feature (manually) to see if it's of any benefit. If so, then an rpm-based switch could be installed to manage the selection automatically. (Something like a "shift light" tach for dragsters, or a modified rev limiter circuit.)

I'll read their site a little more later in the week, too.

Ken
 

SIVAllan

Gold Level Sponsor
As a quick aside, and no intent to hijack this thread, shouldn't the issue be stated as "Holbay cam and distributor? I don't understand a need for a special dizzy setting due to DCOEs alone?
 

RootesRacer

Donation Time
As a quick aside, and no intent to hijack this thread, shouldn't the issue be stated as "Holbay cam and distributor? I don't understand a need for a special dizzy setting due to DCOEs alone?

I dont think so, whats needed in the H120 and whats needed in general DCOE applications are more or less the same.

The need for special advance curves relates to the fact that applications that use DCOEs have two fundamental things in common.

1) They tend to have low volumetric efficiency (due to camming) in the lower RPM revs (and make little vacuum down there).

2) They have no vacuum advance take off port even if they did have vacuum.

This requires full "mechanical" advance, and the lack of VE means the engine needs more timing down low to compensate for the lower compression pressures and subsequent lack of ignition propagation speed.

Stock mechanical advance curves are not even close to what such engines need and running a stock dizzy curve will result in lack of performance at lower RPMs OR over advance on the top RPMs.
 

SIVAllan

Gold Level Sponsor
Thanks Rootesracer,

Perhaps the need could be alleviated if not eliminated by use of a different cam grind, such as the KB grind...

OTOH the motor would no longer be strictly Holbay, but a tweaked Holbay.
 

RootesRacer

Donation Time
Thanks Rootesracer,

Perhaps the need could be alleviated if not eliminated by use of a different cam grind, such as the KB grind...

OTOH the motor would no longer be strictly Holbay, but a tweaked Holbay.

Its not just the cams fault, the weber intake doesnt share flow between runners and the result is poor vacuum in each runner until the engine gets on the cam, then the vacuum is copious.

I ran the same cam I have on my weber motor with a modified SII intake (for EFI) and it made 15 inches of vacuum at 1000 RPM. The same cam with the twin DCOEs intake makes nill at 1200 RPM.

Individual runner intakes really hurt the VE down low.
 

Jay Laifman

Donation Time
I've been thinking about advance curves. FYI, on another thread on this site, they found the H120 advance specs apparently from a list of all Lucas distributors http://forum.sunbeamalpine.org/index.php?threads/weber-dcoe-dizzy-issue.17427/:

Service number - 41239A
Model - 23D4
rot'n - CCW
ECM curve -
RPM 1 - 3000 Advance1±1° - 13
RPM 2 - 900 Advance2±1° - 11
RPM 3 - 400 Advance3±1° - 2
RPM 4 - 250 Advance4±1°
no advance below - 250
vacuum code - No vacuum
Connection -
years -
make - Sunbeam
models - Rapier Holbay H120 engine
Comments -


Looks like Setting #2 is the closest?
 
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