Hi all. Apologies in advance for all the waffle. I'm new to this forum and must admit that I've never taken part before, other than to browse and gain info - but the current state of my xtz750 has pushed me to new limits . . . in short, I'm at my absolute wits end with this thing . . .
. . . bought in mint condition a few years back and absolutely loved it, until it lost it's spark, literally. Main fuse blew - RAC repairman turned up, replaced fuse - multimeter on battery, all good, gave the verdict that was probably just a tired old fuse and gave me the all-clear to carry on. Got another hour and a half motorway riding before it died again. Main fuse blown again, but new fuse wouldn't remedy it this time - result: bike did the ride of shame all the way home on the back of a salvage repair truck :(
Found fault to be a melted down regulator/rectifier (original unit) - in short, because of this; battery melted down, few of the lamps blown, generator/alternator stator melted down . . . and consequently, spark lost!!
Now . . . eons later . . . I have replaced almost everything: new battery, new regulator/rectifier, new ignition coil complete with HT leads, new spark plugs, newly re-wound stator - pickup coil confirmed healthy at same time, and a "new" ECU black box was purchased from eBay from a "reputable" German seller . . .
. . . all these new bits fitted - and STILL no spark!!! The engine still turns over (always has) on the starer motor no problems at all but still refuses to give a spark at the plugs.
I'm thinking the next, and probably last, thing I can try, is to try and confirm that the ECU black box unit is actually working. The new one I got off ebay is supposedly from a reputable seller but I really can't think of anything else that could still be causing no spark. Does anyone know how to test these units?
Any advise what-so-ever would be very, very much appreciated.
ps; I live on the south coast of England, just outside Brighton.

Hi you have significantly changed the main components so this will be difficult to check without seeing the bike and checking you have plumbed it together correctly. Once you have had a beer........

I had a start issue after I bolted my XT600Z together and this was linked to a specific Start Relay; for yours,

https://www.ebay.co.uk/itm/New-Starter- ... 2065345107

It is basically an electrical cutoff switch everything, turned on and functioned as expected but no spark. I would work outwards to inwards to the ECU - check all the electrical cut offs are not playing games , side stand, clutch lever etc.

Sorry not much help

C.

I'd be starting with a visual inspection of all the wires leading from that maion fuse outlet, looking for signs of chafing or cracked wires in case you have a shorting issue. Then I'd be goung back over it again with a circuit tester and checking all OK. Problem could have been intermittent at the beginning but now after totally cracking a wire internally hence the continuity tester. Not sutre what sort of loom it is but if you are able to unplug non essential components that might also be a way of pinning down the fault.

Are you getting power to the coil?

Good luck, sounds like a right royal PITA sort of problem.

Grounds (earths)? ignition switch? kill switch?

Thanks all for your advice, please keep it coming . . . and definitely a lot of beers been drunk while trying sort this bloody thing out - beer fridge is right next to the bike!
I did initially rule out the starter relay and wiring to all the kill switches; clutch, sidestand etc - purely because (and please correct me if I've got this wrong) that there is no problem turning the engine over on the starter motor. Put the key in and turn it on, hit the starter button, and, voila, engine cranks over no worries - just no bloody spark at the plugs. All the switches from clutch, sidestand etc, when in use, will kill everything and I wouldn't be able to crank it over . . . would I?
I have had a friend of a friend, who's an auto-sparky for cars, spent a couple of hours on it, and even he was stumped, though he narrowed it down to either the alternator stator or the ECU.
Turns out the stator was knackered - but that's now been re-wound and proven healthy again - fitted, but still no spark. Which only leaves the ECU - anyone know how to test these? Or can vouch for a reputable seller that sells them? As I say, I have 2 of these now - the original one and the new one I bought of ebay - no idea if either are working. Been told not to buy an original from Yamaha as it would of been sitting on a shelf for all these years and consequently all solder joints etc within it would be dried out and not "as new".
. . . time for a beer I think :) Thanks again everyone.

Here's a brand new one from a company I've gotten a few from not just Yamaha's . Guessed the year but all the 750's use the same ecu .

https://www.hpi.be/item.php?item=CD4613D

The only other thing I'd add is to verify the pulse gen/pick-up coil is sending a signal to the brainbox . It's the component attached to the stator wires and reads the flywheel rpm , they're well known to go bad and when they do you loose spark . Many good stators have been thrown out when it's the pulse gen that is bad since they're attached together .


.

That's really helpful, thank you.
How can I test if the pulse gen is sending a signal to the ecu?
I've put an ohm meter on the leads to the pulse gen/pickup coil, and the reading I'm getting is within specification, but how can I test it in situ, while cranking the engine over? Guessing its an on/off voltage, but how many volts is it and is it DC or AC?
Thanks again.

Mine lost it's spark as well when I first got it, turned out to be the clutch switch gone bad.
I traced the wires back to the 2 wire multiplug, dis-connected it and bridged it on the loom side.
Spark returned, no problems since.

I don't have the info to hand but it should be on the web if you look. Anyway. You can test the coil firstly by testing resistance across them and secondly by essentially hotwiring them in a way that emulates the ECU giving it juice. Only thing is that you can only touch whatever wire is needed for short period of time or else you will burn the coil out. I'd have assumed your sparky friend has done this though and that he has tried wires for continuity. Saying that, an auto mechanic will not have that clutch cutout swith on his,radar as there's no such thing in a car.