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Ignition problems caused by weak flywheel magnetism?

Joined Oct 2007
7 Posts | 0+
First of all I like to apoligize if this subject has been covered before but I've searched the forum without any luck.
Here goes:
I've owned my FE600 -00 since new (it's a FC600 actually but I've converted it), it's all standard and I haven't even tuched the jetting so it has always started on the first or second attempt. Quite some time ago the RH crankcase started cracking between the sprocket and the hole for the swingarm. After years of leaks, welding, silicone and rebuilds I decided to buy a new bike but kept the Berg (and I will never sell it) in bits.
Last year I got hold of a new crankcase and built the engine up again after being in bits in my garage for over 2 years. When it was ready for fire up it wont start and I quickly discover that I've got no spark. I meassure everything and all seem ok so I decide to get a new stator after reading through this forum(but I can't understand how it can fail by sitting in a box in the garage). Still no spark with the new stator. Very frustrating so it must be the coil then. I buy a new one but same again, no spark. All this is done with the lights off in total darkness in the garage without the sparkplug, just the new lead close to the head with all new bits. I've meassured all the dimensions so that it is not the new crankcase that is machined differently making the stator sit in a different position with the respect to the flywheel. I've even tried to move the stator in and out with respect to the flywheel just in case.
Finally in a moment of rage I jump with all my anger on the kickstart, making the engine turn 3 complete cycles, I would think, and finally there is a tiny spark in the dark!
I now try the same with the plug and there is a tiny spark. But not on all attempts (even not when making sure the engine's just gone past TDC before kicking). So I'm trying to fire the bike up again and a couple of minutes later it runs just lovely on idle and there is no missfires. But trying to fire it up again is just a nightmare.
My conclusion is that the flywheel must have lost some of it's magnetism when sitting in the box in the garage!!?? Anyone heard of that before?
Is there a way to re-magnitize the flywheel? The plastic holding the magnets in place have slowly started to fall apart over the years but in other posts it says that it's nothing to worry about and the condition of it hasn't changed since it was last run some years ago.
I've manage to fire the bike up changing to the old stator and coil but now the kickstart lever needs replacing because the hole for the bushing has gone oval and it's cracking here and there .
Thanks for any comments! :wink:
 
DaleEO said:
Have you tried disconnecting the kill switch where it comes out of the coil?
Yes, it's been disconnected all the time. I connected it when I got the engine running.
Thanks
 
Test the magnetism using a screwdriver. lightly hold a medium screwdriver above the removed flywheel. then point the blade towards the centre. it should be attracted to the magnets. it should feel that it tries to ppull out of your grip. if you have to point the blade at the magnets before it goes to them...it has weakened. I have heard of magnetos going weak from storage. Did you place the stator in the flywheel for storage? if so it will not lose magnetism. if they were seperate...it could have lost magnetism!
 
DaleEO said:
And you have checked the spark plug cap for resistance?

And put in a new plug?

The cap is fine, can't measure any resistance. The plug is new, standard.

I'm pretty sure I stored it with the stator in the flywheel, but I can't swear.
Dad's had the same problem on one of his vintage bikes and he had to send it away to magnetize it. Don't know if anyone does that?

Thanks
 
Bultaco said:
DaleEO said:
And you have checked the spark plug cap for resistance?

And put in a new plug?

The cap is fine, can't measure any resistance. The plug is new, standard.

Thanks

That sounds like it could be your problem right there. You should have about 5 kilo ohms of resistance from the top of the plug cap where it screws into the lead from the coil and the bottom where it attaches to the top of the plug.

If you look on the side of the plug cap it will show 5K.
 
i bought a berg that had been in bits for 3 years , the flywheel was grubby and had been sat in water , but when fitted to my bike it worked perfectly,

i read somewhere that true magnets stay magnetic generally for 400 years , where as magnetised steel can loose its magnetism fairly quickly,

i think berg magnets are true magnets,(brittle black things)



does your engine have a good earth,

also if you are using a resistor type plug you could try a non resistive plug of the same heat range
as the voltage is'nt reduced to the electrode, giving you a better spark at the tip.

i went through all of this and it turned out it was a duff brand new ngk to blame,

regards

scrap
 
This is true the stator should be kept in the flywheel, the word for it is a keeper this used to be done years ago when the magnetic materials were mainly iron. Today with ceramic magnetic materials this is not realy needed.
Some of my test flywheels I have here are nearly thirty years old and have not degreded at all.
You generally find that if loss of magnetisum has occured it is due to either the flywheel has been abused with a hammer this disturbs the lines of magnetic flux or some body my have done some arc welding this will totally demagnetise your flywheel.
I have just tested a complete ignition system for a guy who can only bump start the motor on a kick no spark, but on the test rig it performs perfect very low spark threshold 150 200 rpm.
With a problem like this it is either he has got the leg of a woeman are a bad earrth, or the air gap between the stator laminations and the magnets can play a big part in initial spark up.

Regards

Sparks.
 
DaleEO said:
Bultaco said:
DaleEO said:
And you have checked the spark plug cap for resistance?

And put in a new plug?

The cap is fine, can't measure any resistance. The plug is new, standard.

Thanks

That sounds like it could be your problem right there. You should have about 5 kilo ohms of resistance from the top of the plug cap where it screws into the lead from the coil and the bottom where it attaches to the top of the plug.

If you look on the side of the plug cap it will show 5K.

Yes you're right. What I meant is that everything is should be. Sorry and thanks. :oops:
 
It might be so that the new crankcase is machined badly so that the stator sits slightly off center making the spark weaker. I have measured with a feeler gauge through the TDC inspection hole and the gap is about 0.5 mm. With the stator loose in the flywheel this seems right. But maybe it's quite sensitive?

Anyway, I've cleaned the earth connector points REALLY thorough and moved the kickstart a couple of splines to get a longer stroke than I normally have and now it fires up ok-ish. And I'm not kicking like a little girl. Trust me!

But I'm not impressed by the spark at all. It's really weak, but maybe it always been like it. Who knows.
 
Bultaco, try what I call the spark performance test with the plug out and cap removed you should be able to pull 10mm spark from the end of the plug lead on a normal kick, do this though with the lead away from the plug hole. If you find you really have to kick seven bells out of it or close up the air gap to get a spark then it's the stator on it's way out.

Regards

Sparks.
 

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