Originally Posted by Beezageeza

Sounds to me like you have checked out the problem in a logical way. First, carb and fuel/air supply. At one point even changing the carb completely only to be left with the same problem. If it was air/fuel supply, the symptoms would have changed measurably even if the problem remained. So, assume it is NOT the carb...

Next logical thing to troubleshoot is the electrical system. You replaced the coil, reg/rect, spark plug, leads and pretty much everything else in the ignition system. This also made no difference at all.

As the problem occurs in the rev range when ignition advances, anything that controls advance could be the culprit.- TCI and also the sensor in the front of the stator. Many TCI/CDI systems have 2 circuits (one for retard and one for advance) rather than an actual curve, so there is one possibility (dead advance circuit in TCI or the sensor which is part of the stator). Me - I'm too dumb to bench test a TCI so replacing it with a known working unit is the best option.

A left field suggestion...
1. a rat may have crawled up the exhaust pipe and died. It's amazing how much crap a family of rodents can pack into an exhaust pipe. This will have the effect of reducing the amount of exhaust gases that can leave the system and has a similar effect to limiting the air inlet. This happened to me when I restored an old Yamaha XS750 (with straight-through pipes). Had me absolutely stumped why the bike would not run. Took of the pipes and extracted about 10 litres of "rat house" from the straight-through pipes. After that the bike ran flawlessly.

Originally Posted by Beezageeza

I hope you can entertain the rantings of an old grumpy rider. First, check the pipes. This is cheap. Bite me, I'm dutch, and do not like to spend money...

THEN try with a working TCI (better if you can borrow one but you might have to buy).

THEN, think about the stator assembly and try another one.

You will notice I have ordered my diagnostics according to cost. Refer to my initial statement...

Aloha and enjoy the journey

Originally Posted by turboguzzi

the xt's flywheel has only a mark for idle advance, so even if you manged to see it through the tiny M8 hole while pointing a strobe, it will not tell you anything about the advance curve.

so you need a timing/degree wheel too and attaching it to the crank is not that easy on an xt.... done it to adjust my supermono road racer ignition, but it involved turning an adaptor instead of the flywheel nut, plus some sort of sealing of the oil splashing behind the cover.

but that was worth doing in a very highly tuned motor. the stock TCI ignitions are so reliable that you never need to really check timing with a strobe, even less so the advance curve. personally i think that you are barking under the wrong tree.

AFAIK all the TCI's for 1990 and up xt's, including the carb'ed 660's will work. CDI's are a totally different principle, need different flywheel/stator