XTZ750 super tenere shows magic with spark plugs

[diadingo]

Hey guys, my old super tenere xtz750 won’t start due to missing start. But the thing is that I do have spark when the spark plugs are out.
But as soon as I put in at least one spark plug (which doesn’t even need to be connected to cap) the spark is nowhere to be found. It makes me believe that spark dissapears due to lower rpm, hovewer I don’t get why, because it seems to be spinning fst enough and you couldn’t even tell from sound that it got slower.
Wiring harness has been double checked and everything what was suspicious was rewired. Spark plugs are new. I have checked pick-up coil, ignition coil, stator, cap+wire resistanse, diodes, kill switches and all of them are according to the manual specs.
After 3 months on working on the bike I’m out of ideas on what to change. I have tried 2 TCI modules from ebay, because I thought that was the problem. My orginila TCI is damaged, I bought the bike like that.
I really need your help on what would cause the spark to disappear and if it is caused due to drop in rpm or voltage? Jumping car battery has been tried.

[diadingo]

Hey guys, so today I have eliminated 2 variables.
1st: drop in voltage - I have connected seperate battery to the starter moter, so that the system would have it’s own power. No cahnges, when spark plug is in there is no spark.

2nd: drop in rpm - I have connected 24 volts to the starter motor, (nota bene! If you do this, do it with caution, starter may be damaged by prolonged operation) thus making starter spin faster than it does with 12v and spark plugs out. No changes at all. Spark plugs in - no spark. Sprak plusg out - we have spark.

One more thing - I have tryed increasing spark gap to see if it is strong enough and it was. While spark plugs are out spark is normal blue.

From my point of view the only variable left is that the rotor is spinning unevenly while spark plugs are in, thus producing an uneven AC current in pick-up coil. But I don’t get why it should affect the spark plug in any way.

Also today I have found something interesting. I have interchanged pick-up coil wires and there was no spark at all. I don’t get why because pick-up coil produces AC current, so it ahould be of no concern in what way wires are connected, right?

Next step is to change that pick up coil (which seems perfectly fine) if I can find it.

[doggone]

I would suspect the ignition coil(s).
They will often partially fail, producing hard to fathom intermittent loss of spark or very weak spark.

[Robby]

Try running an earth cable direct from the engine to the battery negative terminal.