Originally Posted by Twin-shocker
If you have not fitted a known good or new carb, then you cant eliminate the carb as being your problem. But it sounds more ignition related to me, and very possibly something quite simple.
The most common problem on old CDI systems is insulation breaking down in the source coil when the bike gets hot, and OK again when it cools down. Issues with pulse coils are very rare, but problems in either area will generally mean no spark.
I think you either need to think about looking closely at the carb, and if that checks out ok, and crankcase pressure and compression tests are both good, with reeds sealing properly, find and fit an inductive ignition complete.
New reeds, seal fine. New crank seals, sealing fine. Compression test 90 psi at this altitude is fine, two carbs absolutely spotless that have the exact same problem has to be impossible. I don't think it's mechanical, i really don't.
I guess the ignition coil could be breaking down or something but its not like its a weak spark. It's either crazy mega fat and blindingly bright, or nothing. When you go to kick these over with the plug out checking spark, it sparks quite rapidly, no? Mine kinda just every once in a while sparks, you know?