Author Topic: Testing ignition pick up  (Read 557 times)

Itsme

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Testing ignition pick up
« on: January 22, 2024, 10:10:12 AM »
Hello gents

We've all done it; think we've solved a bike problem, but had to go back to the drawing board when that 'obvious' fault didn't fix a problem.

Up to now whilst trying to get the Mighty Midget (GN250 for those who don't know) running again after a mysterious breakdown I have done the following;

Re-wired the stator output wires which were brittle from heat.
Re-wired the ignition pick-up wires which were similarly aged to the stator wires.
Borrowed the battery off my Inazuma to ensure a good battery as it is only a couple of months old.
Checked continuity of the reg/reg wiring.
Cleaned all carb jets with carb cleaner aerosol.
Replaced float needle and seat and checked float height.
Fitted new coil and HT cap and plug.
Substituted ignitor box for a known working one.

Nothing works. Engine turns over, plug gets wet. BUT and here is another one of those 'must be that then' moments; upon close examination the spark is very weedy looking. It is pale blue and seems to be wandering around the electrode rather than being a strong spark to the centre electrode. So I have now decided that the ignition pick-up must be at fault.

Can anyone tell me how to check if it is that? The manual simply gives figures related to checks using the correct Suzuki test meter. I have a basic multimeter and an even more basic idea of how to use it.

I could buy a cheap Chinese stator and pick-up for about £35, but having spent money needlessly already I would like to have some idea that I might be on the right track this time before denting my wallet again.

Grateful for any suggestions.

Ian

iansoady

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Re: Testing ignition pick up
« Reply #1 on: January 22, 2024, 11:03:41 AM »
No idea of the values for your GN Ian, but for my XBR500 the exciter coil resistance should be 100 -250 ohms.

There are of course lots of stories about fake NGK plugs still around - have you checked that yours is kosher? There's an article in this month's NOC magazine talking about both plugs and plug caps having wildly different resistances to the specified values.
Ian.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

Itsme

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Re: Testing ignition pick up
« Reply #2 on: January 22, 2024, 03:54:41 PM »
Thanks Ian. I found the specs for the pick-up and tested it. It has a range between 160 and 240 ohms and as it read 202 ohms it obviously isn't faulty, another great idea down the toilet.

Interesting what you say about NGK plugs and I have heard lots of stories about fakes. I must have an old champion around somewhere to test the spark.

Honestly I am completely baffled by this as everything seems to be ok, but it just won't start. TBH the Inazuma is doing such a good job I can see the Mighty Midget being covered over and forgotten about.

Ian

Steve H

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Re: Testing ignition pick up
« Reply #3 on: January 26, 2024, 09:12:44 AM »
Is it timed correctly ?, could the woodruff key on the flywheel sheared ? Not unknown

Itsme

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Re: Testing ignition pick up
« Reply #4 on: January 26, 2024, 02:38:25 PM »
Hi Steve

I don't know but it is a good suggestion. I wondered too if the rotor can lose its magnetism? The problem is there are so many small things that could be at fault and working through them all will take time and methodical work. Also I wonder whether a 30 year old bike  which was a cheap commuter has just reached the limits of its use. It does have 52000 miles on it and I can only assume it's intended service limit was a lot less than that so maybe the poor thing is just worn out?

Ian

Steve H

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Re: Testing ignition pick up
« Reply #5 on: January 29, 2024, 09:18:17 AM »
Flywheels can loose there magnetism and it possible to have them re magnetized. Whether you persevere really comes down to how much you have personally invested in the bike, my guess based on the fact you engage on a forum like this bikes are not simply a means of transport. In can be demoralizing but when you get there and fix its a great feeling. I spent about a year trying to sort poor running on an SRX only to find I had robbed a jet out of the carb about 10 years ago and hadnt replaced it :-)

Itsme

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Re: Testing ignition pick up
« Reply #6 on: January 30, 2024, 08:28:20 AM »
Thanks Steve and you are so right, bikes have been my great passion for as long as I can remember. I remember watching the Grandstand scrambling on telly when I was about 7 and telling my mum that one day I would do that. The Mighty Midget is rattly, slow and troublesome, but for some reason is probably my favourite bike ever.

I have got it started using WD40 as a starter fluid and have had mixed results, but at least it started. I am more convinced now that it is fuel related so am following advice from Bill and Ian S about E5 petrol, but first I am totally rewiring the bike and testing every component as I go. Might as well use the off-road time to put right a few bodges carried out over the years just to keep it running.

Strange obsession as whilst this is going on my Inazuma is performing faultlessly (although it still hurts my shoulder to ride it) and yet somehow I know that when the MM is running again it will replace the Inazuma as my daily rider.

Ian