GT500 no spark - FIXED

[MalkyB]

Hi all, almost no hair left now after rebuilding my GT500.  Now I know it was fitted with pointless ignition but this is really doing my brain serious damage.

At every turn I've had dodgy electrics to deal with - the rest of the bike hasn't been an issue at all apart from the electrics!!!

After pulling the very rusty bike apart - who lets a bike stand under a tarp for years....???? - and putting it back together I just can't get a spark.  At this point I have to say I am a Muppet with electrics.  It just means nothing and appears to be some kind of magic rather than some physical entity.  After initially getting no spark I did manage to put a voltmeter across the coils and got nothing so I binned them  I also ordered some new plugs and caps from Rex's Speedshop.  Feeling this was sorted I tried for a spark - nada.

At that point I decided as the rest of the electrics were rubbish and if not failed would pretty soon fail anyway I replaced the CDI unit, Reg / Rectifier with new.  Guess what - yup - no spark.  Yes I had turned on the key!  OK  in that case it must be the ignition coil so I replaced that too.  No it wasn't.  I spoke to a helpful chap at Electrex World who suggested it could be dodgy connection and to hard wire (solder) the connection which I did but - hence the reason for me writing - it didn't help.

Could it be to do with the pickup that sits on top of the rotor...???  There's a red & white wire that leads back to the CDI box which to my mind should be the supply to the unit & the rest of the ignition...???  Should there be a current there when I manually turn the rotor?  If there should be a current and there isn't because wither the pickup is faulty (is that possible...???) or because the wire's broken how on earth am I going to repair that as the wire is covered in clear goo which I assume is to protect it from earthing out...

Edited February 9, 2020 by MalkyB
Muppetry

[Dezza]

Do you have the correct manual for the bike? Personally, I would first check the wiring and all of the ignition system components as described in the workshop manual (genuine Suzuki if possible). Don't forget the obvious such as the ignition switch and the kill switch. If this ancient bike has been left outside for years it wouldn't be that surprising if you have  a dodgy connection somewhere in the wiring

[MalkyB]

Hi Dezza, thanks for your reply.  I have an almost useless Haynes manual - I had one when I originally owned a GT in the 70s.  Back then the bike was only a yeaar or so old when I had it so the manual seemed (to an 18 year-old) quite comprehensive....mainly because I didn't have to fiddle with anything and it was all still shiny & new.

The bike I have now is er.....far from new and suffered the effects of time and weather and Haynes is rubbish with top tips such as 'remove the rotor on the end of the flywheel.....' or 'check the component is in tolerance...'  Are Suzuki genuine manuals available???

I've been in touch with Marcus at Rex's and he's made some suggestions to do with the pick up coil and ignition coil so my fingers are crossed!

[Dezza]

There is quite an extensive reservoir of genuine Suzuki manuals on the interwebs as pdf files. Hopefully someone will be able to post a link. Alternative, a search for past posts for manuals will give you the link. I have used it a couple of times and it's a huge list of different Suzuki models but I cannot rememember those sort of things.

 

The link is here:

 

http://www.manualedereparatie.info/categorii/Suzuki.html

 

It includes some really ancient manuals but not it seems the GT500 It does have some old 2 strokes which may share some of the ignition parts, and hence testing methods, as the GT 500 so maybe cross referencing could help if a manual cannot be found.

Edited February 10, 2020 by Dezza

[Gixer1460]

Yes the Haynes Manuals are a bit simplistic but they do assume a degree of mechanical knowledge / aptitude - they aren't 'Janet and John Build a Motorcycle' LOL! And most of the required tolerances are noted at the beginning of each chapter if they have to be checked. You may be able to track down a genuine Suzuki GT500 manual but don't hold your breath as likely out of print for probably 40 years now although Google may assist! Plus they won't give you an easy way - only use special Suzuki tools obviously.

[Dezza]

Bingo

 

https://www.oldjapanesebikes.com/mraxl_GT_Resource/manuals/t500_service/index.php

[MalkyB]

Brilliant!  Many thanks kind sir!

[MalkyB]

OK - changed everything but the loom and the bike and still no spark.

Can it be something silly like a faulty kill switch?

[bluedog59]

Most electrical problems are down to duff connections/contacts and broken wires. Clean them all and break out the multimeter.

[Dezza]

3 hours ago, MalkyB said:

OK - changed everything but the loom and the bike and still no spark.

Can it be something silly like a faulty kill switch?

Yes

[MalkyB]

That's going to be checked tomorrow....!

[Dezza]

The last 40+ year old bike I restored to stock had terrible wiring. I removed all the loom tape and replaced all of the wires that had gone hard, broken or had dodgy connections and also replaced most of the connector blocks (freely available on the interwebs). I also stripped and rebuilt the handlebar switches and replaced the ignition switch. Sometimes cheap OEM switches are available. The GT500 will likely use the same switches as many Suzuki models of that era but they are very expensive unless you are very lucky. Pattern switches are usually very poor and not worth the hassel unless you are desperate. Personally, I would remove the loom and remove the tape from the loom. I am guessing a horror show will be revealed. Please post pics

[MalkyB]

The ignition switch was duff - no power to the black / yellow feed to the CDI box,  A spur runs to the kill switch which I had thought was dodgy but clearly wasn't after sparks flew when I flipped it and had a temporary feed hooked up!

I've ordered a new ignition switch (for a X7 but was the only one I could find with 4 wires to the plug and 2 brown feeds for the parking lights) so that should sort out the lack of power to the CDI but......still why no spark now there's power to the CDI box..???  The coils (including HT cables plus & caps), pulsar oil, source coils, CDI and reg/rectifier are all new so all new wires.  There's continuity from the CDI to the coils and with power (via a separate test feed) to the CDI now a fluctuating current to the coils.....everything but a spark!!!!!!!!!!!!!!!!!!!

This isn't likely to be something even sillier like no earth from the cylinder head when I hold the plug against it is it...???

 

[Dezza]

2 hours ago, MalkyB said:

The ignition switch was duff - no power to the black / yellow feed to the CDI box,  A spur runs to the kill switch which I had thought was dodgy but clearly wasn't after sparks flew when I flipped it and had a temporary feed hooked up!

I've ordered a new ignition switch (for a X7 but was the only one I could find with 4 wires to the plug and 2 brown feeds for the parking lights) so that should sort out the lack of power to the CDI but......still why no spark now there's power to the CDI box..???  The coils (including HT cables plus & caps), pulsar oil, source coils, CDI and reg/rectifier are all new so all new wires.  There's continuity from the CDI to the coils and with power (via a separate test feed) to the CDI now a fluctuating current to the coils.....everything but a spark!!!!!!!!!!!!!!!!!!!

This isn't likely to be something even sillier like no earth from the cylinder head when I hold the plug against it is it...???

 

The switch will come apart. Do this in a plastic washing up bowl to catch all the titchy little ball bearings, contacts and springs. You will likely find corroded contacts. The wires can be replaced too. The switch is common to a whole load of GT models, and I think early GS750s etc.. There are (too) many pattern versions of these switches on the market. Most of the ones I have seen are of poor quality, not in the same league as re-buildable OEM items.

Have you had the frame powder coated? If so you may indeeed be getting no contact between the engine and frame. This is easily checked and if so remidied by running a remore eath lead from the cases to the frame. Check the loom and all of the ignition wiring especially. There is a great diagram of all the ignition system on the online manual link above (I looked earlier).

[MalkyB]

Many thanks Dezza - yes the frame is powder coated but I can get a good contact from the battery back to ground on the engine.

[Blubber]

You now have power to the cdi, but how is the spark triggered?

Basically ....Does it still have points or a aftermarket signal generator?

[MalkyB]

The spark should be triggered by the pulsar coil on top of the flywheel rotor.  No points as GTs had (aptly named) pointless ignition

[Blubber]

Aha... did not recognise that name.

I can only assume you checked the resistance values?

There seems to be a discrepancy in the manual.

Or this link

Edited February 16, 2020 by Blubber

[Poldark]

2 hours ago, MalkyB said:

The spark should be triggered by the pulsar coil on top of the flywheel rotor.  No points as GTs had (aptly named) pointless ignition

So is it a similar system to what many lawn mower engines use?  That sounds like how my B&S engine ignition works.

[MalkyB]

Yup - same thing as your Briggs & Stratton

[MalkyB]

Hooray!!  Many thanks to everyone that helped - After replacing almost everything it seems I should have just.....replaced everything.

I ordered a NOS rotor, arrived today and within 10 minutes I had sparks.  The one thing it shouldn't have been - it was!

I'm one happy bunny

[bluedog59]

I do like a happy ending.

Time to make some blue smoke.

[Ted M]

Awesome glad it's sorted. Now post some pictures or it never happened. 

 

[MalkyB]

Oh - it happened alright

I'll get some pictures up over the weekend of all the new parts.....there are a few

[MalkyB]

The culprit....!