Post by thread:SV: [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. Dale --- We are Dyslexia of Borg. Fusistance is retile. Your ass will be laminated. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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. -- Mike Poulton spam_OUTmpoultonTakeThisOuTmtptech.com MTP Technologies KC0LLX -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> -----Original Message----- > From: Dale Botkin [SMTP:.....daleKILLspam@spam@BOTKIN.ORG] > Sent: Friday, October 25, 2002 6:41 AM > To: PICLISTKILLspamMITVMA.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 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>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. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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}

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 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

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. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> -----Original Message----- > From: Attila Muhi [SMTP:.....attilaKILLspam.....TELORAY.SE] > Sent: Friday, October 25, 2002 9:39 PM > To: EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.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 -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestspam_OUTmitvma.mit.edu