DM2 v 25D Dizzy

Technical questions and Maintenance advice post in here please
Post Reply
User avatar
philipangus
Posts: 796
Joined: Thu Aug 13, 2015 8:55 pm
Location: Bangor Northern Ireland
x 3

DM2 v 25D Dizzy

Post by philipangus »

HI

My dizzy is a DM2 with points. I have bought a replacement dizzy complete with electronic ignition, but I see that its a 25D version. Will this be OK? Is there any operational difference between the two that I need to be aware of?

Also I intend to use silicone HT leads as recommended for the electronic ignition as they have a higher resistance which helps protect the electronic components (apparently resistance spark plugs are not recommended instead). However i've read that resistance spark plugs give a stronger spark than non-resistance ones - so my question is could I use resistance plugs as well as the silicone leads or is this unnecessary or even undesirable?.

Grateful for any thoughts on these matters.

Many Thanks

Philip
Bill
Posts: 729
Joined: Tue Jan 07, 2014 5:37 pm
Location: Taunton

Re: DM2 v 25D Dizzy

Post by Bill »

Often wondered myself what the difference is between he DM2 and the 25. I've fitted electronic to my (late) DM2 and Powerspark is great. I never changed the leads. They never advised me to and I do believe that elsewhere on this forum there is a thread saying that it is unnecessary. I await the technical experts advice again but personal experience it is a waste of money if you already have good copper leads.
User avatar
philipangus
Posts: 796
Joined: Thu Aug 13, 2015 8:55 pm
Location: Bangor Northern Ireland
x 3

Re: DM2 v 25D Dizzy

Post by philipangus »

Bill

Out of interest what make and model of plugs are you using?

Philip
User avatar
Nelly
Posts: 655
Joined: Wed Oct 22, 2014 6:47 pm
Location: Hampshire

Re: DM2 v 25D Dizzy

Post by Nelly »

Bill wrote:Often wondered myself what the difference is between he DM2 and the 25. I've fitted electronic to my (late) DM2 and Powerspark is great. I never changed the leads. They never advised me to and I do believe that elsewhere on this forum there is a thread saying that it is unnecessary. I await the technical experts advice again but personal experience it is a waste of money if you already have good copper leads.
You need some resistance in there somewhere (otherwise the interference effects the electronics), so with copper leads that means you'll need resistance in the plug caps or in the plugs themselves.

We have copper leads and the resistor version of the plugs.

Oh dizzy had already been changed to the 25D so we converted that to electronic. As the advance curve will be different to original (and fuel etc) I don't expect it matters much whether you use DM2 or D25. (But you need the right kit to match the dizzy).
Felicity and Sam, Owners of 'Nelly', 1955 Black 4-Door A30
Owner and Club Member Since 2014
Southampton & New Forest Club Member
Tight Yorkshireman
Posts: 4933
Joined: Wed Apr 29, 2009 11:03 pm
Location: Sheffield

Re: DM2 v 25D Dizzy

Post by Tight Yorkshireman »

Ask the supplier they should be able to advise

John G
John (Tight Yorkshireman)
First referred to as the Tight Yorkshireman in editions of the Clubs Spotlight: Autumn 1996 Page 40 and Autumn 1997 Page 15
Bill
Posts: 729
Joined: Tue Jan 07, 2014 5:37 pm
Location: Taunton

Re: DM2 v 25D Dizzy

Post by Bill »

philipangus wrote:Bill

Out of interest what make and model of plugs are you using?

Philip
Phil, NGK's. Work well. On a 1000 mile trip to France this year I got 43mpg with a fully loaded car. I have the standard suppressed plug caps. If you are in any doubt about this, give Powerspark a call. They always answer the phone and are very helpful. Do I understand from the rest of this thread that physically the DM2 and the 25D are interchangeable, with only the advance profile to differentiate?
User avatar
philipangus
Posts: 796
Joined: Thu Aug 13, 2015 8:55 pm
Location: Bangor Northern Ireland
x 3

Re: DM2 v 25D Dizzy

Post by philipangus »

Bill and all.

Thanks for all your advice. I'm just waiting for some braided wire to run a separate line from the switched fuse so as to keep the original wiring free (but of course insulated off) in case I want to or have to swap back to points in an emergency (it would be a bit expensive to carry a spare electronic module).

I also been using NGKs and they got me to Hibaldstow and back last year - some 700 miles and got 45.4mpg. My major issue on the trip was fuel vaporisation due to the engine bay overheating in the really hot weekend sun. I'm going to try and insulate the fuel line from the pump to the carb to see if that makes any difference. Of course I'm still using the Zenith which probably is more prone to vaporisation.

Anyway on the dizzy I've already got some new silicon/carbon leads and i'll fit therewith standard non-resistance plugs and see how that goes. Just need some warm weather to get out to the garage!

I'll keep the forum posted on how I get on.

Regards

Philip
Bill
Posts: 729
Joined: Tue Jan 07, 2014 5:37 pm
Location: Taunton

Re: DM2 v 25D Dizzy

Post by Bill »

Hi Phil,

I resisted going SU for a long time but eventually did. The Zenith (every Zenith I've ever had) suffers from evaporation resulting in churning the starter if the car has been stood. The way to get them to work best I found was to put 2 emulsion block gaskets in. This seem to eliminate flat spots and improves starting. Keep us posted.
User avatar
Nelly
Posts: 655
Joined: Wed Oct 22, 2014 6:47 pm
Location: Hampshire

Re: DM2 v 25D Dizzy

Post by Nelly »

Bill wrote:Do I understand from the rest of this thread that physically the DM2 and the 25D are interchangeable, with only the advance profile to differentiate?
No, there are two types (early and late) of DM2 and one type of 25D when it comes to getting the right shaped points kit. Also, the advance curves are specific to the application, so there's a huge variation of these between cars. I guess the off the shelf modern built dizzys take an average!
Felicity and Sam, Owners of 'Nelly', 1955 Black 4-Door A30
Owner and Club Member Since 2014
Southampton & New Forest Club Member
Bill
Posts: 729
Joined: Tue Jan 07, 2014 5:37 pm
Location: Taunton

Re: DM2 v 25D Dizzy

Post by Bill »

Nelly wrote:
Bill wrote:Do I understand from the rest of this thread that physically the DM2 and the 25D are interchangeable, with only the advance profile to differentiate?
No, there are two types (early and late) of DM2 and one type of 25D when it comes to getting the right shaped points kit. Also, the advance curves are specific to the application, so there's a huge variation of these between cars. I guess the off the shelf modern built dizzys take an average!
I wasn't thinking so much of the points difference, but the actual fit of the dizzy in the car. Obviously you will need to buy the electronic system to suit whichever but physically they can be interchanged?
Dave Clark
Posts: 5896
Joined: Mon Apr 21, 2008 1:00 pm
Location: High Wycombe, Bucks

Re: DM2 v 25D Dizzy

Post by Dave Clark »

Yes. Generally speaking, most Lucas distributors will physically fit.
Bill
Posts: 729
Joined: Tue Jan 07, 2014 5:37 pm
Location: Taunton

Re: DM2 v 25D Dizzy

Post by Bill »

Dave Clark wrote:Yes. Generally speaking, most Lucas distributors will physically fit.
Thanks Dave. I have a late DM2 which is fitted with Powerspark and is fine but interesting nevertheless.
User avatar
philipangus
Posts: 796
Joined: Thu Aug 13, 2015 8:55 pm
Location: Bangor Northern Ireland
x 3

Re: DM2 v 25D Dizzy

Post by philipangus »

Getting back to my original question. I have a late DM2 at present with points in a 948cc with 26VME. If I fit a D25 with electronic ignition will I notice any difference (better or worse) in performance because of the different distributor, ignoring the upgrade to electronic ignition?
User avatar
Nelly
Posts: 655
Joined: Wed Oct 22, 2014 6:47 pm
Location: Hampshire

Re: DM2 v 25D Dizzy

Post by Nelly »

If both work properly, I would guess no
Felicity and Sam, Owners of 'Nelly', 1955 Black 4-Door A30
Owner and Club Member Since 2014
Southampton & New Forest Club Member
Post Reply