My Targa has always been a bit slow to start - engines turns over but slow to pick up. No probs with battery or starter motor, so I put it down to fuel. The starting has got steadily worse over the last 3 years, but it’s not the fuel - today I got it going but it was only running on left cylinder. Took it round the block when it stopped and smoke came up from underneath front of tank. On inspection, left hand coil was smoking (but left cylinder was working, not the right). I’ve obviously got a duff left coil, but could the problem be caused originally by something else? I’ve put on new HT caps and spark plugs and fuel system is working fine, so I’m assuming it’s electrical. Is it normal for coils to degrade over time? Any advice gratefully received!
Coils don’t usually burn out and smoke unless they have been receiving a constant power feed for a long time. Have you left the ignition on for a long time by mistake? I blew one up riding home from the Ride to the wall a couple of years ago when the electronic ignition packed up. It was firing on one, the other side was permanantly feeding power into the coil. That did the same thing, went pop and smoke from under the left side panel was a bit diconcerting!
What ignition system do you have?
Have the points stopped opening or has the elctronic ignition failed open?
My left coil is on the right and the right coil is on the left, it makes the HT leads run better. Try checking the wires to see if this is the case on yours.
Thanks for swift replies, chaps. I haven’t left the ignition on for a long period, but I suppose I’ve been trying to start it up quite a few times. It has the standard electronic ignition with the light blue plastic covering and the alignment marks are in the right place, so I haven’t touched it. The coils are fed left to left, right to right. The left coil was smoking from the front - I’ve attached a photo where you can see a hole burnt through with yellow wire showing, just behind the front attachment pillar. This happened when I finally got it started and took it for a rest ride, after 1 minute, so as you say, probably the load went through the left coil and proved too much. So I don’t think that the starting problem was originally down to the coil as the starting problem existed before the coil went. I confess to being very inexperienced with electrics, but if the battery and starter motor are OK, then the problem must exist between the spark plugs and the starter motor. Years ago I had a Dnepr 650 which constantly blew condensers. Is it possible to check a condenser? If it’s a bad connection or wire then I’ll need to use a multimeter to check resistance? I’ve never done this before so should I disconnect the battery first? The electronic ignition units look OK (i.e. not burned) but is it possible to check them too, given the cost of them? But why would both go? So I’m looking for a common factor, or - if it is the right pot EIU gone, then could the left coil become overloaded, as you indicated, Don-Spada? The fuses are OK.
Mulling over this during a lunchtime chicken sandwich, could it be that either a) the coil has degraded over time, causing starter problems before totally packing up or b) as Don-Spada infers, the electronic ignition control unit (EICU) on the right cylinder packed up, causing the power to go to the left coil which burnt out? Do the EICUs (£140 each!) just pack up or do they degrade over time? Can I check whether they are OK or not? I need a new coil anyway, but I don’t want to install it only to be blown again if it wasn’t the coil in the first place.
Not sure how you would check the black boxes. I’m not that familiar with the ignition system on these. Try doing a Google search to see what comes up. The important thing to find out is if it is triggering. Check the leads down to the pick ups, see if there are any bad conections.
Not sure what aftermarket systems are available for a Targa rather than replacing with a secondhand unit of unknown pedigree. Gutsibits sell a Sachse system.
https://www.gutsibits.co.uk/pr/TheShop/index.php?f=d&Model=&q=coil&spPage=2
Your right in saying that coils degrade over time so it may be that a new set of coils are needed, which would leave you with one old coil spare which could be substituted for the burned out one as a trial, ie one new coil and one old coil on the dodgy side. This would mean that if there was a repeat of the burning then youve only lost another old coil and your search would then be focussed on the ignition system itself.(hopefully its only a coil gone down) As has been mentioned the triggers are the main thing to check as its usually a defined air gap that has to be maintained and they can get crud in there
CHRIS P
Thanks Chris, I’ve ordered a new coil from Gutsibits so I’ll swap over to check. Being an electrical newbie, I spent last night pondering the wiring diagram and continuity checking with the buzzer on my multimeter - never done it before but it’s interesting to compare the diagram to the actual wiring and connectors. It’s opened up a whole new world! I’ve even uncovered some butchered wiring to the front brake switch which I’ve never noticed before. So far all the connectivity is there between the coils and the EICUs, but there seems no way of checking them - they are totally enclosed. When you say the ‘triggers’, do you mean the pick-ups? Are they behind the blue plastic cover of the electronic ignition until in the place where points would normally be situated? It looks all pretty clean in there. Here’s a picture of the burnt out coil - it is bonded in plastic so I can’t take it apart unless I hacksaw through.
You could try rotating the engine slowly and see if the triggers are working. I would assume they work the same as a set of points and basically are a pair of switches to earth.
On the coils, you should find one wire that feeds power into the coils (Switched to live when you turn the ignition on) this wire is usually white.
The other wire to each coil should basically intermittently connect to earth, so with a multi meter set to resistance, one probe on the chassis and the other on the second coil wire. As you turn the engine over, you should see the circuit make and break.
It is the point where the circuit breaks that causes the HT side of the coil to spark. You just want to know if it is connecting on and off.
I haven’t drawn a 750 Targa diagram yet but here is the link to Carl Allison’s one. Beware that on some of his diagrams some of the colours can be wrong, but this will help you to trace what connects to where http://www.thisoldtractor.com/guzzi007/schematics/1990_750_Targa.gif
I cannot find a good enough copy of the factory wiring diagram to be able to check the colours for you.
Thanks chaps,
Chris,
I’ve seen the old tractor wire diags but I have the original owners handbook with a good wiring diagram, which seems to be reflected accurately on the bike, except in a few places where previous owners may have replaced the wire ends with black - tracing a short way back they revert to the book colours. Unfortunately, a scan doesn’t reproduce the diagram in clear detail, whereas a photocopy is better. I’ll try a better scan and make it available to you; failing that I can send you a photocopy.
Don-Spada,
The coil wire colours are indeed as you say. I’m hoping to get the new coil soon, so will swap 'em over and check as you suggest. Another thought: are the electronic ignition control units interchangeable? Presumably they just fire on signal from the pick-ups/triggers. If the coil section proves OK, then the idea is to swap over the control units to see if the respective pot doesn’t fire, then I’d know I’d have to part with cash for another one!
Incidentally, I’ve found the Haynes Motorcycle Workshop Practice Techbook to be invaluable. Unlike most servicing books which just say, for example, “test the circuit with a multimeter”, this book actually tells you how to do it and the reasons why. For mechanical novices like me I’d thoroughly recommend it!
You can check the triggers are switching now before your new coils arrive as you would disconnect the wire from the coil to test it.
Not sure if you would need the ignition on or not, probably on to activate the black box.
Is this article of any help:
https://isavetractors.com/blog/do-you-keep-burning-out-ignition-coils-here-is-why/
Could well be - thanks Jef. I’ve been distracted by other stuff this weekend (my wife has interpreted the lockdown as ‘pile on more DIY jobs for me’!) but I’m just off do some more tests as per advice above, fit the new coil and whilst I’m at it will change the HT leads too!
Hello All. Finally got to spend some time on the bike problem. I’ve checked all wires and connections and they are OK. Pickups were clean and tidy, so I took off the 2nd coil (right) only to find that it had blown too! Now this puts things in a slightly different lights I’ve two blown coils after a long period of starting problems. My theory is that it isn’t the ignition timing /electronic ignition control units - something is a root cause of the problem on both cylinders: Checking the wiring diagram and all the wires, it could be the regulator (in the Targa it is a joint regulator/rectifier evidently) is duff, which caused, over time, the coils to degrade due to the voltage input wobbling about (technical term!), which accounts for the increasingly bad starting problems and then finally kaputt. Can one check the regulator? There was no continuity between the wires going in and out. The only other thing on that circuit is the alternator but surely not?
Best way to check the rectifier / regulato is to start the bike up and put a voltmeter across the battery terminals. Not sure if you are in a position to be able to do this at present though. You should get around 13.8V maximum. If it goes much over that, you have a problem.
As I assume the bike has 2 separate pick ups and two black boxes, then there isn’t much else that is common to both circuits.
It was the electronic ignition wot dunnit!
Bit of a delay whilst I waited for parts, but at least the bike’s got some brand new coils and HT leads out of it and I’m now intimately familiar with the wiring diagram! Turns out that difficult starting, usually associated with fuel/carb issues (as I did) is a precursor, which gets slowly worse, which if it isn’t identified as a faulty electronic ignition (it wasn’t), will blow your coils (it did!). So these pesky Saprisa black boxes aren’t digitally either working or u/s - they degrade disgracefully over time before really throwing out their toys and going supernova on the coils.
I contribute this to the forum as a cautionary tale to all those who may suffer the same problem in future. Thanks to all who offered advice and helped get me back on the road!
Good to hear you have it sorted and thanks for letting us know what the problem was.
Did you replace the entire ignition if so what with for future reference
CHRIS P
Decided to go the whole hog and go for a Silent-Hektik system. It doesn’t work out much more than replacing the Motoplats or the alternative Sachse system and is allegedly more robust. The main lesson is that if you have rough running and cannot put it down to fuel delivery, suspect the electronic ignition straight away, if it is Motoplat (I’ve now heard several anecdotes about the original system fitted to late '80-s-early '90’s bikes).