Cut it out!

Hoping someone could help me diagnose a niggly issue.

My ex police special XJ750 has a bad habit of randomly just cutting out. It’s an electrical issue going by the way it dies. Exactly like hitting the kill switch.

Bike will be running mint then suddenly die. Occurs at idle or under load. If I try and start it with key or crash start immediately after it won’t start again **unless I toggle the ignition switch off and on**. Once I’ve done a power cycle with ignition (off then on again) it fires straight back up like nothing happened.

It’s done it since I had it and I’ve completely re-wired her and taken carbs to church. Overall runs great now.

I’m suspicious that since I’ve re-wired it (new loom) and carbs, spark and fuel etc all check out that perhaps it’s an issue with the CDI? Or maybe coils?

Has anyone else had a similar issue or know what the common failure modes are for ignition modules?

Any help greatly appreciated.

 

Welcome to the forum. When you start the bike wiggle the wires going into the ignition switch to see if it cuts out. But it sounds like a faulty ignition switch. Unlikely the TCI or coils. If it runs well and then instantly cuts out it's a wire or switch issue. Even if it was related to the TCI you have two coils for four cylinders and two transistors in the TCI. They won't all fail at once. Check all the loom connections first and try and isolate the problem before getting any parts. If you have the glass fuse box change it for a blade fuse box. The original ones those clips break that hold the fuses

 

Thanks Franz. Appreciate your reply. I’ve done a bit of electrical work in the past and have removed the factory loom completely. It’s been re-wired (barebones) by me recently. I’ve replaced all factory switches, relays and fuses. This issue existed before the re-wire and now after. The only original electrical items are the TCI, Reg/Rec and coils plus their OEM connectors which is what has made me suspect them. I’ve done the ‘wiggle test’ and can’t replicate the fault. It seems really unusual hence me wondering what the failure modes were on TCI and coils.

When it does cut out it will turn over fine but not fire until I’ve cycled ignition toggle switch- again, makes me suspicious of the TCI or coils as there’s not much left so far as I can tell.

 

If your TCI failed totally bike would not run at all. Left ignition coil operates cylinders 1 & 4 and right coil cylinders 2 & 3. As the bike is running and the ignition switch from what you say is new might be a fault in the original wiring connectors you referred too. TCI you would need to plug in a spare one to check if it fixes the problem. If one of the ignition coils were faulty you would have only two cylinders running. From my experience total failure of ignition is usually not TCI or ignition coils. Is there anywhere a wire with damaged insulation is touching the frame? Do you have a Haynes manual? Have you checked the sidestand switch?

 

Toggle switch meaning kill switch on handlebar?

 

Yes- it’s a toggle I’ve added which operates an ignition relay.

Cool, thanks for your help, that’s what I was looking for. I’ll assume the TCI and coils are fine for now and revisit the connectors / switches. Cheers

 

Let us know when you get it fixed, or if you have any more questions. Cheers.

 

Cheers. One more quick question if I may- to remove factory connectors do you slide a thin metal tool in between the metal crimp connector and housing to depress the tab then pull out? They seem pretty well stuck in there.

 

After you have had a shut down and recycled to restart does the shut down happen again after a similar period? A repeating cycle? Is the toggle switch of heavy duty enough for the use? Could the switch itself be overheating and reconnecting when it cools down? Did you use a circuit breaker in the harness instead of a fuse somewhere? I guess that is obvious enough you would have already thought of it.

 

RE: connectors. Yes. There is a tiny tab that you can depress to slide the individual connectors out of the block.

 

Thanks Fuller. There is no regular frequency to the shutting off. It can happen randomly at idle in the garage without any input from me or while riding down the road. It’s truly bizarre. As for the switch, the switch just operates a fused relay so next to no load on the switch itself. In fact- the way it’s wired I can turn the ignition off and the bike will still run until I flick the kill switch which disrupts the power supply circuit to the coils.

I’m very suspicious of the remaining OEM connectors now so might make that the next job and replace them when I wire up lights etc. seems odd though that cycling the ignition switch off and on again even for a split second is enough to make it fire again. I can even do that while riding and let the clutch out without stopping and it’ll fire straight back up. If I don’t cycle the ignition though it simply will not fire. Just turns over indefinitely.

 

I use these to fit new uninsulated connectors.




This is one of the tabs you need to flatten Fuller refers too to get the wire out of the plastic connection. I cut them off if bad and replace them. The one pictured is a 6.3mm uninsulated connector.

 

Okay, that description changes thoughts. It sounds like something is saturating electrically. I really, highly doubt it is the TCI. That type of ignition either works or it does not, not really anything in between. Another thought that just occurred is to check your grounds, especially to the frame, for being loose or having paint under them. A trick on another family of motorcycles is to run dedicated ground wire from the battery, or ground buss, to the coils. Just some thoughts. Good luck.

 

sounds like what my friend with a a Kawasaki K1000 experienced. It turned out to be grounding.

 

Interesting, Looking at wiring diagram and from reading other posts I didn't believe that the coils actually needed a ground to operate?

Currently all the grounds required to make the bike run are taken back to the battery via a common lead, and also a heavy gauge link to the engine, on a clean mount point. I deliberately didn't run one to the coils. Would it be worth putting one in?

I still need to install all the wiring for lights etc so I might set something up then. In saying that, before I re-wired it (and was still having the problem, much more frequently too) the PO had used the coil mount bolts as common grounding points for a lot of the accessory circuits.

Thanks for everyones thoughts, it all helps! I got a spare connector disassembled too using a flattened paperclip haha. Will tackle connector replacement in the new year.

 

Found this on another forum. Sounds quite like my issue. Thought others may find it interesting. Might split the TCI and see if there are any obvious issues and for some testing.

 

https://www.xjcd.org/TCI_repair

 

Resoldering the TCI joints, worth a try and inexpensive. A bunch of us saying they don't usually fail could easily be wrong. And remember when running your ground wire that it need to be as large as the positive feed wire, all those electrons need to get back to the battery. Good Luck!

 

Just a thought.....Does your machine have a sidestand switch?
Those tend to get dirty and gummy, causing exactly the problem that you are experiencing.
If you have said switch, peel the boot back and spray contact cleaner at the base of the plunger as you move the plunger in and out of the housing. Once it moves very freely, just follow up with a spray of dry-film lubricant and put the boot back on. I clean mine annually.

 

Thanks k-moe. There are no interlock / safety switches currently left connected, I ran a new bare bones loom when I re-wired it.

 

Was fuse box replaced? - mine was causing intermittent cut out. (I didn't see a reference to it above).

 

Hey, sorry if this was included in what you replaced, but do you still have the original kill switch in addition to the toggle you added? I actually had my 750 cutting out similarly until I was leaving the carb clinic the other year and it wouldn't start at all. After futzing with it for a while we ended up taking the switch apart and one of the connections had a single strand of wire left where it was soldered in and that crumbled when I touched it. After replacing the switch I was back on the road.

 

Thanks CrazyGnat and Cgutz- fuse block, ignition and ALL OEM wiring loom, switches and relays etc have been removed. I’m confident it isn’t electrical baring perhaps a handful of OEM connectors which are still there but have been cleaned and look fine.