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'[EE]: CDI for 2-stroke, anyone done it?'
2002\10\25@014249 by Dale Botkin

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Anyone done CDI for a 2-stroke engine with magneto?  I don't know if I'd
even need a PIC for anything...  it doesn't look too hard, so I suspect
there's something waiting to jump up and bite me half way through.

Engine in question is that of a '55 Vespa 150cc scooter, if anyone cares.
I'm thinking more and bigger sparks would be better.

Dale
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Fusistance is retile.
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2002\10\25@022147 by Mike Poulton

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Dale Botkin wrote:
> Anyone done CDI for a 2-stroke engine with magneto?  I don't know if I'd
> even need a PIC for anything...  it doesn't look too hard, so I suspect
> there's something waiting to jump up and bite me half way through.

CDI units are available for 2-strokes.  Insane modelers use them to
help get 8HP out of weedwacker engines for RC boats.  AFAIK, there's
nothing terribly tricky about it.



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2002\10\25@031534 by Michael Rigby-Jones

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> -----Original Message-----
> From: Dale Botkin [SMTP:.....daleKILLspamspam@spam@BOTKIN.ORG]
> Sent: Friday, October 25, 2002 6:41 AM
> To:   PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject:      [EE]: CDI for 2-stroke, anyone done it?
>
> Anyone done CDI for a 2-stroke engine with magneto?  I don't know if I'd
> even need a PIC for anything...  it doesn't look too hard, so I suspect
> there's something waiting to jump up and bite me half way through.
>
> Engine in question is that of a '55 Vespa 150cc scooter, if anyone cares.
> I'm thinking more and bigger sparks would be better.
>
CDI gives potentialy bigger and hotter sparks, but the spark duration is
much lower than an inductive system, which is mainly why most all systems
these days are inductive.  To get multiple sparks (a la MSD system), you are
going to have to have a fairly high current inverter to be able to charge
the cap up in anything like a reasonable time (or do they use a bank of
caps, sequentialy fired?).  I know that with the MSD system you get less
sparks as engine speed increases.

There was a rash of CDI projects around in the usual magazines about 10-15
years ago.  IIRC the main issues are a powerfull high voltage inverter that
can drive a short ciruit happily (discharged cap), a capacitor designed for
high current pulse use, and of course a reliable SCR firing circuit.  A very
simple design can be found at
http://home.labridge.com/~wnoble/WN_articles/CD-ignition-SK.pdf

Regards

Mike

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2002\10\25@035732 by Alan B. Pearce

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>CDI gives potentialy bigger and hotter sparks, but the spark duration is
>much lower than an inductive system, which is mainly why most all systems
>these days are inductive.  To get multiple sparks (a la MSD system), you
are
>going to have to have a fairly high current inverter to be able to charge
>the cap up in anything like a reasonable time (or do they use a bank of
>caps, sequentialy fired?).  I know that with the MSD system you get less
>sparks as engine speed increases.

This is an area where a GTO Thyristor is potentially useful. I have not done
it, but do remember it being a proposed application when GTO's first came
out.

Instead of letting the capacitor discharge through the coil in one large
zap, use the GTO to start-stop-start-stop the discharge for as many times as
you have sufficient energy in the capacitor.

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2002\10\25@055906 by Alvaro Deibe Diaz

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I've just restored a 1961's MotoVespa (Vespa made in Spain) 150S (150cc, 4
speed selector). It would be nice to have CDI in it...

Alvaro.

P.S.: I'm having problems with engine overheating. This is a common place
with original Vespa (Piaggio) piston-cylinder during break-in. I'd like to
have (PIC based?) temperature sensing, and perhaps automatic spark shut-off
to prevent engine seizing. Hmmm sounds very interesting...

{Original Message removed}

2002\10\25@063545 by Peter L. Peres

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On Fri, 25 Oct 2002, Dale Botkin wrote:

*>Anyone done CDI for a 2-stroke engine with magneto?  I don't know if I'd
*>even need a PIC for anything...  it doesn't look too hard, so I suspect
*>there's something waiting to jump up and bite me half way through.
*>
*>Engine in question is that of a '55 Vespa 150cc scooter, if anyone cares.
*>I'm thinking more and bigger sparks would be better.

Imho a CDI for that engine is overkill but an electronic breaker would
help. CDI for magneto engines is problematic because there is no normal
place to hook up the CDI elements to and electrical circuits are usually
weird. Otoh it could be a great hack project. There are several Vespa
enthusiasts sites, including mods etc, and a magazine. Search first imho.

Peter

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2002\10\25@092936 by Dale Botkin

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Thanks everyone for the responses.  I think I'm going to wait until I have
it running to decide if I'm going to try to do anything new with the
ignition system.

There are commercial CDI systems available for Vespas, but i have not
found any that will fit an engine as old as this one.  Having had a look
at the stator coils and wiring on the scooter, It lokos like it's in
better shape than I had thought so I'll try cleaning that up and doing any
repairs.

Alvaro, check out http://www.scootrs.com, they have a CDI system for 60s Vespas,
it may or may not work with yours but they do respond well to email
questions about it.  Good luck!

Dale
---
We are Dyslexia of Borg.
Fusistance is retile.
Your ass will be laminated.

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2002\10\28@042722 by Michael Rigby-Jones

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> -----Original Message-----
> From: Attila Muhi [SMTP:.....attilaKILLspamspam.....TELORAY.SE]
> Sent: Friday, October 25, 2002 9:39 PM
> To:   EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject:      SV:      [EE]: CDI for 2-stroke, anyone done it?
>
> CDI = diesel injection ?, 2 - stroke, hmm..  Interesting.... sparks ...
> diesel ??!
>
CDI = Capacative Discharge Ignition, nothing to do with Diesels!

> >I'm thinking more and bigger sparks would be better.
> >
>
> Absolutely. In aircraft piston engines, with 2 separate ignition systems,
> you will see a significant rpm drop if you switch off one of them ( guess
> around 5%). (Probably the drop will be even more significant if you switch
> off both...) Alfa Romeo has some car engines with two spark plug per
> cykinder ,btw...
>
Two spark plugs per cylinder (in cars) are used to reduce the maximum flame
path, and therefore burn the compressed mixture more quickly.  The OP is
probably not is a posistion to machine the cylinder head to accept another
spark plug, but wants to use multiple sparks which allows reliable
combustion of non-optimal/exhaust gas poluted mixture.

Regards

Mike

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