Distributor Advance

[JACKJABBA]

I have checked the +2 workshop manual (page 14)and compared the data for the 41189A distributor with the data for the same in the Miles Wilkins Lotus Twin Cam book (page 168 -169). The advance figures are the same but for different RPM.

Crank RPM / <span style='color:green'>ADVANCE (+2 manual</span>) / ADVANCE (Wilkins book)

1000 / <span style='color:green'>Static (10</span>) / Static
1250 / <span style='color:green'>12.5</span>/ Static
1500 / <span style='color:green'>14.5</span> / Static
1750 / <span style='color:green'>17</span> / Static
2000 / <span style='color:green'>19.3</span> / Static
2250 / <span style='color:green'>21.5</span> /
2500 / <span style='color:green'>24 max adv </span>/ 12.5
3000 / <span style='color:green'>24 max adv </span>/ 14.5
3500 / <span style='color:green'>24 max adv </span>/ 17
4000 / <span style='color:green'>24 max adv </span>/ 19.3
4500 / <span style='color:green'>24 max adv </span>/ 21.5
5000 - 6500 / <span style='color:green'>24 max adv </span>/ 24 max adv

Any idea which is correct ?

I have a 43D4 fitted which is meant to replace the 41189A and it gives a curve like the +2 manual. I have twin 40 dcoe and c type cam

[BillGavin]

It looks like the +2 manual is giving specs for distributor rpm, while Miles wilkins is using crankshaft rpm.

[JACKJABBA]

That would make sense of the figures, so I guess my dizzy may need new springs or replacement. .

Regards Jack.

[BillGavin]

Jack -

What are you seeing for a curve with your current distributor?

How far off the specs is it?

- Bill

[BillGavin]

oops - got that backwards

The Plus 2 Manual give crankshaft RPM
The Wilkins Book gives distributor RPM

I also checked my Elan manual, crankshaft RPM

All three sources give identical results

I also check a Lucas Ignition Manual: it's specs vary
by a few degrees. but I haven't tried to analyze the variance.

BTW it's usual practice to check distributor advance in
deceleration: you bring the engine up to speed above your
highest datum, then drop the revs to each datum point and
record the values. Just the reverse of the way its presented
in most tables.

[JACKJABBA]

I should have read the ignition chapter of the Wilkins book beter, it says on page 168 that Lotus got crankshaft and distributor rpm confused in the manuals. Distributor rpm being half of the crankshaft rpm. Therefore the Wilkins figures are correct when using crank rpm.

I will plot my curve tomorrow and see whats going on, but it wasn't looking good

2000rpm (crank) 20 deg

[type26owner]

Jack,
Did you fix the scatter problem as per my instructions? Does the timing mark now appear to be stationary when observed using a timing light when the rpms are held steady? It should not jitter about by more then the indentation's width of the timing mark on the pulley.

On my engine when it's physically at TDC the timing mark is actually indicating 7 degrees BTDC. It's just a little bit off. <_<

Bill,
Is obtaining a copy of the Lucas Ignition Manual an Ebay endeavor only?

Just acquired a Sun 504 dizzy machine. Didn't know at that time I had to also have the power module to fire the strobe for the optical and hall effect equipped dizzies. Ouch! BTW, my son provided me the contact number off of the Mopar forum for Roger Kunz at 815-344-6538. He's the guy to know for any replacement parts for any obsolete Sun diagnostic tools.
Regards,
Keith

[BillGavin]

Keith -

The copyright date is 1972, so Ebay may be the best
source.

Tuning Lucas Ignition Systems
ISBN 0 85113 06 3 1

It was published by a company in England that published
quite a few titles relating to motoring and motorsports:

Speedsport Motorbooks
(Interauto Book Company Limited)
Bercourt House, York Road, Brentford,
Middlesex, TW8 OQP, England

They also published my treasured Mini Tuning books by
Clive Trickey - good info, and what a great name for a
racer

- Bill

[type26owner]

Many thanks Bill!

Jack, try this link for help. A clue as to what the problem might be is if the advance weights and spring area is covered with rust. That would be special form of rust called fretting corrosion.
<a href='http://www.telusplanet.net/~chichm/tech/lucastuning.pdf' target='_blank'>http://www.telusplanet.net/~chichm/tech/lu...lucastuning.pdf</a>
Good luck,
Keith
p.s. Would suggest everyone download this file before it possibly disappears off of the web.

[JACKJABBA]

The dizzy does not have any scatter, but the advance is out. If the static is set at 10 deg, it is giving full advance by 2250 rpm (crank), looks like the primary spring may not be doing its job. I have taken it apart and it all appears to be ok.

I phoned around today and have managed to get hold of a new (not reconditioned) 43d4 (set for an elan ) for ?99 inc VAT, which is obviously a very good buy. The Guy is down to his last couple. I should have it by the weekend, so will post the contact details here if it proves to be what its ment to be.


The engine idle is at the moment is very smooth after the carb rebuild, so when the new dizzy is fitted I should have better progression, I hope.

[JACKJABBA]

Does anyone know a UK suplier of the springs used in the Lucas Distributor. I have found that the secondary spring is too long and is playing no part in its operation. I know it is ment to be loose, but the cam hits its stop before the spring is taking effect.

Regards Jack.

[steveww]

Alternatively give up on old mechanical systems and go for mapped ignition. Not original of course but a much better solution. QED do a complete kit based on DTA but there are a number of other options. I would avoid the Weber Alpha as you can not remap the system yourself as they do not supply the software.

[JACKJABBA]

Can anyone with a 43D4 distributor let me now what the id number is on the distributor they have. (ie 41845A)

Also does your 43D4 give any advance between 1000 rpm and 2000 rpm.

Regards Jack