Testing CDI units

[bob]

Guys, clearing out my garage and have a box of CDI units, can't remember which ones work and which don't.
Is there any way of testing them, with a multi meter for instance, so I know which ones to bin
Cheers in advance

[monument7]

Try them on a running scooter ?

[bob]

Try them on a running scooter ?

That was going to be my last resort, just wondering if there was a simpler way of doing it

[Donnie]

Nope, that's the easiest most direct way apparantly :-/

[Paulnobodyimportant]

I've asked that question before and they are all correct, no way to test. And they can be really temperamental, such as total or partial failure such as not review right. So for £30, it's worth keeping a spare and it's a quick switch on the side of the road.

[Knowledge]

Better still, build a bracket to take two CDI units, so you can switch between both at the side of the road very quickly.

[bob]

Agree with Martins comment, although my back up is just tie wrapped on

[soullad]

This has often puzzled me, How many P range/ T 5 Vespa riders carry a spare CDi ? Hardly any I'd wager. So why should it be different for Lambretta riders? Market flooded with cheap Ducati copies? Stator plate output too erratic? Poor earthing?
Buy the best you can afford, and if you are a belt and braces kinda guy, carry a spare.

[Captain Pugwash]

This has often puzzled me, How many P range/ T 5 Vespa riders carry a spare CDi ? Hardly any I'd wager. So why should it be different for Lambretta riders? Market flooded with cheap Ducati copies? Stator plate output too erratic? Poor earthing?
Buy the best you can afford, and if you are a belt and braces kinda guy, carry a spare.

+1

[HxPaul]

Guys, clearing out my garage and have a box of CDI units, can't remember which ones work and which don't.
Is there any way of testing them, with a multi meter for instance, so I know which ones to bin
Cheers in advance

I've been out for a ride today and my scooter was running really rough,I thought at first it was dirt in the carb.I cleaned out the carb and the scooter started ok,so I started to ride home.After about 5 miles it began to run rough and then it cut out.After letting it cool for about half an hour it started again,this time it ran for about two miles before cutting out.This happened another twice.In the end I replaced the cdi (I bought this,a Ducati cdi in a kit cotaining,stator,flywheel and Ducati regulator from SR,it had done just over 100 miles)and it ran perfect for the rest of the day,apparently the cdi was breaking down every time it got hot,once it cooled down it started again.

[rossclark]

Vespa CDis used to be prone to cracking round the top of the box where the resin is and letting water in so you always used to carry a can of wd40 to spray on it on wet days.

I have a theory that most people bolt the CDi directly to the frame or to a bracket bolted directly to the frame and that they fail because of the increased vibrations. The Vespa ones are bolted to a rubber mounted bracket and they vibrate less anyway.

[coaster]

Guys, clearing out my garage and have a box of CDI units, can't remember which ones work and which don't.
Is there any way of testing them, with a multi meter for instance, so I know which ones to bin
Cheers in advance

I've been out for a ride today and my scooter was running really rough,I thought at first it was dirt in the carb.I cleaned out the carb and the scooter started ok,so I started to ride home.After about 5 miles it began to run rough and then it cut out.After letting it cool for about half an hour it started again,this time it ran for about two miles before cutting out.This happened another twice.In the end I replaced the cdi (I bought this,a Ducati cdi in a kit cotaining,stator,flywheel and Ducati regulator from SR,it had done just over 100 miles)and it ran perfect for the rest of the day,apparently the cdi was breaking down every time it got hot,once it cooled down it started again.

I have never experienced an intermittent CDI failure, they always fail completely for me. Your symptoms align very much with a failing LT coil which are usually down to failing coil insulation and easily proved with a multi-tester....keep an eye on it for a while yet

[coaster]

This has often puzzled me, How many P range/ T 5 Vespa riders carry a spare CDi ? Hardly any I'd wager. So why should it be different for Lambretta riders? Market flooded with cheap Ducati copies? Stator plate output too erratic? Poor earthing?
Buy the best you can afford, and if you are a belt and braces kinda guy, carry a spare.

+1

I also believe vibration plays it's part, rubber mounting the cdi is a good idea imho

[HxPaul]

Guys, clearing out my garage and have a box of CDI units, can't remember which ones work and which don't.
Is there any way of testing them, with a multi meter for instance, so I know which ones to bin
Cheers in advance

I've been out for a ride today and my scooter was running really rough,I thought at first it was dirt in the carb.I cleaned out the carb and the scooter started ok,so I started to ride home.After about 5 miles it began to run rough and then it cut out.After letting it cool for about half an hour it started again,this time it ran for about two miles before cutting out.This happened another twice.In the end I replaced the cdi (I bought this,a Ducati cdi in a kit cotaining,stator,flywheel and Ducati regulator from SR,it had done just over 100 miles)and it ran perfect for the rest of the day,apparently the cdi was breaking down every time it got hot,once it cooled down it started again.

I have never experienced an intermittent CDI failure, they always fail completely for me. Your symptoms align very much with a failing LT coil which are usually down to failing coil insulation and easily proved with a multi-tester....keep an eye on it for a while yet

The cdi I swapped the Ducati for was an bgm box.Once fitted the scooter started and ran perfectly for the rest of the way home (about 25 miles )If it is the LT coil on the stater that is at fault would it run ok even when it gets hot just by changing the cdi.I have a multimetre and can check the stator plate as in Sticky's book,will the resistance reading show up as being faulty when the stator is cold or should I run the scooter until it gets hot and then check it.If the Ducati cdi isn't at fault I dont want to send it back to SR for a replacement.

[Captain Pugwash]

There's nothing stopping you checking the voltages coming out of the lt coil and the pickup when it's actually running.

Using a basic ac/dc digital multimeter.
You just need to pull back any covers on the end terminals that connect to the CDI from the stator.

from memory (AND I MIGHT BE WRONG with the voltages AS ITS A LONG LONG TIME SINCE I DID ANY OF THIS KIND OF STUFF WITH A MULTIMETER)
A running engine will produce about 60 volts ac from the lt coil when the engine is running and it's connected to the CDI , this is normally measured between White and green from the stator then multimetered at the CDI.

And a figure of about 0.6 volts dc from the pickup normally white and red from the stator again metered at the CDI.

When checking the (LT coil voltage) switch the meter to (ac 200 volts scale) connect the multimeter black lead neg - to the White from the stator at the CDI.
Connect the multimeter red lead Pos + to the green from the stator at the CDI.

Start the scooter and check the voltages produced.

The volts should climb steadily from around 35-40 volts then peak at about 60 volts even though the engine revs higher this is because there are switching circuits and diodes controlling the peak voltage.

To check the Pickup voltage you now need to switch the multimeter to the dc 20 volt setting (don't use the ac setting as from memory I don't think it will give the correct reading)
You need to connect the multimeter black lead negative - to the red from the stator at the CDI.
Connect the multimeter red lead positive + to the White from the stator at the CDI.

Start the scooter and the voltage will start low at around 0.4 volts at tick over or just above and then should climb with revs to around 0.6 volts. It should level off even if you increase the revs, again it's because of the internal components in the pickup and CDI.

It's a simple test and if you take a good working stator and do these checks, then write down what the stator puts out at the CDI this when it's running correct then you can always do a simple quick check later if it fails and see where the differences are.

This is a simple multimeter test I've used a few times, but if your using an oscilloscope you can see much more of the electrical wave forms and peak voltages, which doesn't look quite the same as the multimeter results.

Test lead probes are just carefully held against the connectors at the CDI. Probably easier with two people, one starting and revving the scooter the other holding the meter.

I did once have quite a few old Lambretta electrical stuff that I'd worked out and written down but that's about 30 years ago, but most of its lost now.

[Captain Pugwash]

I do have an old Innocenti tech sheet somewhere and it explains a way of testing a CDI, but for the life of me I can't find it anywhere.

I think it may have got lost In the last house move

[coaster]

I do have an old Innocenti tech sheet somewhere and it explains a way of testing a CDI, but for the life of me I can't find it anywhere.

I think it may have got lost In the last house move

Someone posted schematics of the Ducati and SIL CDI's a few years ago and the circuitry was slightly different which won't make it any easier lol

[Captain Pugwash]

I do have an old Innocenti tech sheet somewhere and it explains a way of testing a CDI, but for the life of me I can't find it anywhere.

I think it may have got lost In the last house move

Someone posted schematics of the Ducati and SIL CDI's a few years ago and the circuitry was slightly different which won't make it any easier lol

Your more than likely right Coaster, but if I do ever find it I will scan it and put it up on the forum. It could be useful.

I think I got it from Nick banks when he had Nickspeeds scooter shop in Garston.

Nickspeeds stopped being a scooter about 20 years ago I think it's a tattoo shop now.

[Nelly]

Any wiring diagrams or Schematics could be useful.
I'd be very interested in seeing the CDI schematics if anybody does have them. I've often wondered what was going on in that elusive box of magic!

[Dimitrios_231]

There is a very basic schematic at the following page,
I don't know how to post a SWF file here.

http://www.vespamaintenance.com/elec/cdiwork/index.html