+1 for the above post, remove the restrictor from the header pipe....
i recently worked on a mates son's pw80,
i modified the airbox intake by removing the rubber factory tubes in the top of the box that suck in clean air it sit in like a grommet.
then cut the top of the air box out about 20mm wider on each side and 10mm at the front and rear, and made another steel intake out of some 20mm inside dia pipe (x4 tubes instead of the factory 3x 14mm tubes) and welded them to a 75mmx50mm piece of 1.6mm thick steel, bolted that into the top of the airbox and it makes a fairly big difference, more power and more induction noise too, nice
i also made a custom muffler to replace the rear restricted one, sounds quieter/deeper now. there is also another restriction coming off the back of the expansion chamber, i removed that
i had to richen the mixture by moving the clip down one slot on the carby needle to compensate for the mods, it can now almost keep up with his yz80/85?
the cdi unit on the 90's onwards bikes are rev limited too, if you get one off an pre 84 model they are not restricted
have you tried unplugging the cdi and spraying the contacts in the plugs with crc/wd40? might be worth a try, could be a bad wiring connection somewhere
also the coil maybe starting to fail, when it gets warm it may be arking out,
can you take it to a bike wreckers and see if they will let you try another coil on it?
good luck
