No Spark Cyl2&3 - 83 XJ750

Hi All,

I recently replaced the resistor caps (5k NGK) on all 4 cylinders and spark plugs (BP8ES - couldnt find BP7ES). After connecting everything back up, I've found that I'm getting spark on 1&4 (gonna call this coil1) but not on cyl 2&3 (gonna call this coil 2)

Checking primary resistance on coil 1 and 2, get 2.5k each. Secondary coil I get 22k each (side note - 2x 5k caps so not sure why it's hitting 22k) doesnt sound right but coil1 is working, expect coil2 should at least spark.

Checking pickup coil, both pickups are around 110 ohms.

Battery is not an issue, tested with spare
Tested with old spark plugs in 2&3, still no spark
Tested with old resistor caps in 2&3, still no spark

Bike was running prior but Cyl2 resistor cap was loose and eventually disconnected from the lead. Looked at fixing it but the connections were dirty so decided to replace all 4 caps. Have also had an issue with RPM not displaying however thought it may have been a tachometer gauge issue (was like this for a couple of weeks prior to no spark issues)

Any ideas where to look next?

 

Chack that the primary lead didn't become disconected. The Tach gets its signal from the 2/3 coil.

 

Sorry, should have mentioned i've checked connectors too. Have continuity from primary lead into the CDI.

When connecting multimeter to AC voltage between orange (coil1/4) to ground it's showing around 3.2-3.8v when cranking. Switching over to grey (coil2/3) and ground it shows around 0.4-0.7v.. points toward faulty CDI?

 

Pulled apart the CDI and did some testing on the circuits, found no obvious faults although not ruled out. Did find that someone else had messed around in there.. lots of dodgy wiring and soldering. Fixed that at least. Put it back on the bike, no change (as expected)

Switched the coil packs for testing spark, 2/3 started sparked and 1/4 nothing.. so it's not the coils.

 

TCI. Yes there is a difference, and if you ever go to work on yours in more depth it will come in handy to know that.

The common TCI failures (which really aren't that common) beyong solder joint failures are the electrolytic caps leaking, or the diodes corroding, or the transistors failing.

It sounds like you have no issue with working on electronics, so....

http://www.xs11.com/forum/showthread.php?t=38224&highlight=tci+repair
http://www.jetav8r.com/Vision/IgnitionFAQ.html

Or you could source a good used TCI.

Or
TCI upgrade options?

 

Did some testing inside the TCI and seems like the transistor for coil 2/3 is faulty. Will continue to test other components and see why it failed.

In case anyone else is interested in future, the transistors are SD1113 for the TID14-21 29R-10 TCI. Not sure how this compares for other TCI models.

Seems the SD1113 are hard to find in Australia.. I'll be trying to source one then will report back.

---- edit -
Curious to know, sourcing another TCI, I expect the 'Type' would need to match? for me it's the TID14-21 29R-10. I did search around and found a lot of other models but not an exact match. 29R stuff appears to be rare..
Any idea whether they're interchangeable?

 

The transistors tend to be damaged when someone checks for spark without having a good ground path for the secondary coil. You may not find a fault, but it is wise to look before relplacing the transistors.

TCI info here, about halfway down the page: xj-parts-catalog-section-d-electrical-system.44641
More detailed info here, again about halfway down the page:
the-information-overload-hour.27544

This thread should help you find alternative transistors.
circuit-board-level-help-required.37190
Darkfiber hasn't been on here in a while, but you might start a conversation with him and see if he can be of help.

New TCI units are being made by a few aftermarket suppliers.
aftermarket-ignition.45931

 

Hello all! Im new to here but I have had a few xj bikes. Right now I have an 1982 XJ750 that im having some spark issues with. I didnt mean to bump in with another concern but im really lost here. I recently purchased an 82 750 maxim that had been sitting since 16 so I removed the carbs cleaned the bowls and installed a fairly ok battery. I was able to get it to fire up off ether until it took gas and idled great. Came back the next morning and it will crank and crank all day but not start. I pulled the wires and tested spark and have nothing. I removed the fuse box and just bypassed all the fuses to eliminate anything that could be causing it meaning I twisted all the wires together except ignition. I had a small inline fuse laying around that I connected to it. Everything seems backwards. I have a plug out laying on the head with a wire connected and when i turn the kill switch on everything dims but the atari does not run its self checks. Now the weird part... when I turn the kill switch off i get a spark from all 4. Im really so confused. The bike had its first night in the garage since 16 I would have thought it would have been happy about it. Anything that could possibly lead me in the right direction would be awesome.

 

Hi Stoybob, very odd. Did you end up sorting this out? A multimeter and a wiring diagram are gonna be your best friend here. If you get spark then its safe to assume the ignition side is good enough at this stage. Sounds like you may have a short somewhere and you're probably gonna need to start at the beginning with a multimeter and start tracing from the battery through to the main switch and kill switch and forward. Obviously there should be no power passing the kill switch in it's off position, double check your bypassing and consider reinstalling the fuses as they're there for safety reasons. Test the installed fuse box on the multimeter to make sure there's continuity across them rather than bypassing. Until the kill switch is operating correctly with the multimeter then I wouldn't attempt to start the bike

 

Just an update, I got replacement transistors, replaced them and no change. Then found a faulty resistor, replaced it and others. Also replaced other components in the TCI but eventually was out of my depth and decided to purchase an aftermarket TCI from Ignitech (https://www.ignitech.cz/en/vyrobky/tcip/tcip.htm). Ordered it with plug and play connectors, arrived in Australia after about a week and bike started up straight away.

Still got a few other issues to sort out before taking it out on the road for a proper test but so far seems to be working