AutomaticAdvanceUnit (AAU) NC 250

[Dave354]

Here is my a unit…..

[bw_nh]

good afternoon Dave (and list)

Thanks for the photo- so THAT is a 28-degree AAU, from what I understand.

The ebay aa367B version, which IS on this side of the Atlantic, closes in a little more than 3 hours.

I re-read a posting by Dew-Cat-Tea-Bob, written in 2010 (I am not sure how to copy-quote it, but here is some relevant information for someone who might want to find it...

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Re: Recharging 250 MK1/MK3 Magneto
Postby DewCatTea-Bob » Mon Jan 11, 2010 10:12 pm

By Desmoto-M.3 : ...
\=================

I think he is writing that a 28 degree AAU can be used in place of an 18-degreeAAU... but on re-read, I wonder if he is saying that the this would be a swap on a battery-ignition version, but he is perhaps NOT suggesting the swap on an AC ignition system...

My GOAL is to get this scrambler to start/run, but... I do NOT expect to go on long rides with it, likely NEVER at night... I just want it to start properly.

I know I SHOULD put in an electronic ignition, and better alternator stuff (and maybe a battery, or a capacitor), but I think it might just be better to make it work as originally intended.

Do I understand correctly that an 18 degree AAU will help the bike to start? Or am I mistaken in that? I want it to start... I do not want it to be MORE difficult to start, I do not want to encourage kick-backs... I just want the bike to start properly.

With three hours to go on the ebay listing, I am tempted to make a bid, and add that part to the small pile of spares that I have.

Advice? Bid/buy the aa367B to improve things? Acquire the 359 that Dave has? Or stick with the static no-advance unit I have?

SIncerely,

Bob Woolner
Hillsboro, New Hampshire

[Dave354]

Hi Bob, I’m a bit confused when you say yours is a fixed timing? What is fitted there at the moment? Surely as the engine revs there is a need for ignition advance? Personally, I’d go for the e bay one first… try it and see… if it’s still not right, sell it on eBay and try mine?

Dave

[bw_nh]

Good evening Dave- and list-

I passed on the aau367B on ebay.

I have owned this 1966 250 scrambler for almost 40 years. When I acquired it, it was mostly original. In the late 1980s, I took it apart, (didn't open the motor) , cleaned all, repainted it blue, trying to match what was the original blue. (yes, I know most were black-paint, but mine was definitely, originally, blue.

Back then... 35-40 years ago, after re-assembly, it ran well.

It sat in my barn here in New Hampshire for years. For the past few summers, I have tried unsuccessfully, to get it running again.

This is why I thought the ignition was "fixed" Look at the parts diagram that I have- part number 280.

https://www.flickr.com/photos/99202596@ ... 306655755/
https://www.flickr.com/photos/99202596@ ... 306655755/

And, if you look at this electrics manual, page three...

http://motoscrubs.com/Ducati_Electrics/Ign_Flywheel.htm bottom of the chart... for the "250 motocross"...

Note the timing is set "advance with still engine" at 38 degrees, with nil automatic advance, with total advance listed as... 38 degrees. That seems "fixed" to me, and if part number 280 is what is in my Ducati, then obviously there is no advance, because there is no advance mechanism.

HOWEVER... I just looked closely at my scrambler (in the barn) , and found that the engine number is 94186. WHICH is later than the number 87902, which is listed on that page three of the chart. Which means, maybe I do have an AAU already, that is set with a "still engine", at 21-23 degrees, with 18 degrees of advance.

Which would mean, that I gain nothing by purchasing another aau367B, IF I already own one.

Which means, I am a dope, for not investigating THAT before calling out to find one to help with my starting problem.

I also have a 1966 Mach I, also owned for 45-ish years... which ran VERY well back then. The Mach I is mostly original, although I painted the tank black, back in 1974 or 1975 if I remember. And the resurrection of that Ducati has gone well. No issues there. Only with the Scrambler.

Therefore... I think I will go silent for a bit, and just read more back postings on this forum, about the AC ignition systems, and some time in the next few months, I will try to sort out WHY this 6v no-battery AC system... won't fire up.

There are other photos of the scrambler, and the Mach I in that flickr album that I linked earlier.

Thanks to all, so far, I will let you know how it goes... when it goes.

Sincerely,

Bob Woolner
Hillsboro, New Hampshire USA

[Jordan]

Hi Bob,
The 250SCR-Mark3 parts list you posted shows it doesn't have an AAU, rather it has a fixed ignition camshaft - something I didn't know existed.
Something to check is whether it's is in the correct position, as it's possible to have it half a turn out.

[Dave354]

Well everyday is a school day! I never knew there was such a thing as a fixed ignition system on these engines. You need to pull off that points plate to let us see what’s behind it!

Regards

Dave

[Bevel bob]

From what i remember there was a system that started with 18 degrees and advanced to 36 and another that was fixed at 38 . Imagine trying to kick that over. Bump start only . Thats why I suggested a system like that the Monza and Mach1 got in the uk. Still not good but ,workable.

[Jordan]

there was a system that started with 18 degrees and advanced to 36

That arrangement would be at the discretion of whoever is timing the ignition, with the standard parts (maybe lengthening the adjustment slots).
Full retard at 18 BTDC seems risky.
Some surgery on the AAU could provide a larger advance range, and less likelihood of damage to machine and rider.

[bw_nh]

Here is my a unit…..

Good morning Dave354- and List-

I sent you (Dave) a private message- can you contact me? I am interested in purchasing your AAU, if you still have it!

Sincerely,

Bob Woolner
Hillsboro, New Hampshire USA

[Bevel bob]

Hi Jordon, The system I was referring to was set at 18 degrees initial advance and advanced to 36 total . I seem to remember that systems with high initial amounts of advance were regarded as suitable for bump starting only ,particularly when owners realised how fragile the KS parts are. I suspect that most owners of bikes with these unfriendly ignitions either have no intention of any practical use or soon realise that the bikes are for trading or display only. I ride my 250 NC M3 and have used it for sole transport when away on holiday for 5 x 10 days in the Isle of Man . A bike is just junk if not a practical rider.