Can a guru please explain for me?

[paulharris01]

My nephew has just bought a Tianzhong 1900. One of those little chopper things - 50cc. Just to start off, the previous owner had done some welding on it and suggested the CDI (think thats what it was called) needed to be replaced. We did that but no change.

There is no current running down the spark plug lead at all. No battery so i presume its a magneto system.

The thing I noticed yesterday when he was showing it off to me, is that when he kick starts it, every now an then the kicker seems to slip (or at least makes that kind of noise).

I really want to get this going for the poor sod. Am I correct in thinking that the best place to start would be checking the magneto? How do i do this? Could the twit with the welder cooked something in there?

Even if you want to ramble on and tell me how the magneto creates a spark and sends it to the plug - i'll read it.

One other thing, should the electrics be earthed as I dont see an earthing wire?

Any suggetions would be appreciated - as I want to be his hero.

Thanks

[Johnj]

Try looking here.

[paulharris01]

That was a really interesting link. Thanks for that.

Now, what i need to know is :

How do i know if the condenser and points are creating a spark and can this be checked without removing the fly wheel?

Is there a specific gap between the magno and the flywheel?

Paul

[Johnj]

How do i know if the condenser and points are creating a spark and can this be checked without removing the fly wheel?

If I wanted to check if I had spark I'd open the points cover, turn on the key, and manually open the points. You should see a weak spark at the points. If you pulled the spark plug, reconnected the lead, and laid the plug against the engine when you manually open the points there should be a big blue spark at the plug.

[flynrider]

If the OP truly has a magneto ignition, he'll have to turn the engine over while looking at the exposed plug to check for a spark. There's no juice in the ignition system unless the mag is turning.

[paulharris01]

Thanks for all the info. I'll be heading up his way in a week or so.
It doesnt have a key or battery. In saying that, i dont even know if it has a magno. I just presumed it did because it isnt electric - so how does it get power for a spark? Or is that the job for the CDI?

Im hoping from the info receiced that i will simply replace the points and condenser (the welder may have cooked them) and I can get a current running.

As it stands, there is no spark at the plug because power isnt even there.

Many thanks all and a happy new year.

Paul

[flynrider]

If there is no external power storage device (like a battery), then it's likely that the bike has a magneto driven ingition. It's an old method of ignition, but still used in applications where you don't want to depend on an external power source for ignition (for example, lawnmowers and airplanes).

The magneto generates its own spark as it turns with the engine's rotation.

[pchast]

Hi....

I've done some of these with lawnmowers. The magneto is a laminated iron wire wound piece, either under and inside or outside of the flywheel. Often just cleaning the flywheel surface and the mag surface with some sandpaper is enough. Reset the gap to just pass the fly wheel in the neighborhood of .015.

I've never 'cooked' the points and condenser with a little welding.

Cleaning with something like a nail file and resetting the points is likely needed. IF there is significant pitting or buildup on one side of the points replace both.

Luck with it,
Pete

[paulharris01]

thanks Pete,

Thank sounds like a good idea. To be honest, im not sure at the moment if it has a magneto. Im just assuming as I cant figure out what creates the power to the CDI as it doesnt have a key or baterry. It wasnt made with one.

Cheers

Happy new year

Paul

[pchast]

Paul

Well, its most likely that since its the ruggedest, simplest, system out there.

The only other method, though rare and troublesome, I've heard of is a small can size generator and a large Capacitor to replace the battery. This is used on race cars like formula v( i think). they do anything to reduce weight. I think its too expensive for that bike.

Have fun.
Pete