CDI units. what are they all about anyway? By hellspigeon (Read 910 times)

[hellspigeon]

I was thinking about buying a new cdi unit for my 157QMJ. But I'm not really sure what I'm looking for. There's some cheapies on amazon for like 8 to 15 bucks. They look like the stock replacement and some claim to be "No Rev Limit" others say " advanced timing curve". And then there the ones like Naraku that run for up to 50 bucks. What is the CDI for? Which one should I get for my scoot? And should I buy a better ignition coil while I'm at it? Any advice would appreciated.

[kz1000st]

A CDI shortens and intensifies the duration of the spark at the plug. It stands for "Capacitive Discharge Ignition". It basically stores electrical energy until it gets an outside signal from your flywheel and then releases it in microseconds. It also boosts the intensity giving you a hotter spark.

Basically, as with anything, a cheaper CDI may not function as well but works. I bought one once from Scrappy for like $12.00 and the scooter just hummed. Maybe 30 or 40,000 miles down the road it might have given me trouble but who cares? It worked.

[tvnacman]

Cdi is what generates spark, it stores up energy and then releases it in theory at top dead center, that makes the spark plug spark spark to ignite the fuel in the combustion chamber.

There are many claims out there of hotter spark. What is hotter spark? Spark is the action of electrical arcking when pontential difference is present between two conductors. The higher the voltage/pressure the easier to ark across the conducters .

I would like to know how you measure the temperature of a spark?

There are cdi's that will delay spark and also make it spark sooner.


John

[twowheeler]

They are notorious for advancing to the point where it makes starting difficult. I remember seeing someone here that got a variable timing CDI that does not advance at startup.

PS I have tried both orange and blue versions and have gone back to stock. Not seeing and benefit on a stock scoot.

[FrankenMech]

I have the blue version, and it works OK, no problems at all. I have several stock black ones for backups. I do need to test them to see if they all work.

[Alleyoop]

Go and read this:
Alleyoop

www.scooterdoc.proboards.com/index.cgi?action=display&board=trike&thread=7116&page=1

[twowheeler]

A guy did a comparison on 49ccscoot.com at found NO difference in 0-30 times between stock and the others...

[Alleyoop]

0-30 mph on a 49 scoot won't help(HAHA). Also what was he going by did he check the timing with a timing light or just by feel. Advanced timing gives you a little more power because the spark plug fires earlier. The reality is a motor can make more power if it fires just a hair after top dead center. Reason it is about to start the downward stroke off the compression stroke BUT that puts a lot of stress on the crank and they don't last so long.
Alleyoop

[tvnacman]

Al, Brent did a video on a few cdi's. The stock cdi acted like a variable timing cdi. Aside from his video I have not come across a stock cdi that acts in that way.

The problem here is the Chinese copy cosmeticly from one another. The way they fuction are different , I have had to go through many identical looking cdi's to find the one you have.

John

[Alleyoop]

anybody has a link to his video.
Alleyoop

[tvnacman]

If this link does not work I will get it to you later I get home .



John

[twowheeler]

He checked the timing on each.

[shop242]

Check this out.. Go old school.. Put a 3 degree advance key on the flywheel.. Must have a machine shop to do it unless those chinese screwers have it already ( doubt they do )

[Alleyoop]

Very good Video, but I did notice his scoot was to far retarded to start off His timing was almost on the "F" when it should be on the "T".

And yes slotting the Pickup is one way to advance the timing and you can also buy Offset Woodruff keys that will advance or retard about 2-3 degrees.

As for mph I would not expect that from advancing the timing just more torque due to the little extra power.
Alleyoop

Got to love it, he also complained about harder starting with a fix advanced CDI.

[twowheeler]

I get so mesmerized in the series of videos hes done.