Here are few two stroke blog spots. All of them are in Greek language but still include lots of nice and interesting photos, info, links etc. 1) This one is a blog by Bill(GR), a two stroke head mostly messing with Yamaha mopeds and twin cylinder bikes. Check out his blog at terrezos2t.blogspot.gr 2) This is a blog by Kostas(GR). An untamed youth mostly working on Honda Nsr250 bikes. Check out his blog at twostroke-greece.blogspot.gr 3) And last but not least, a blog by Spiros(GR). It hasn't been updated for years but still has tons of info & links about Yamaha Rd350 bikes. Check out his blog at 31k-gr.blogspot.gr
Frits Overmars is a well known tuner and very knowledgeable on Aprilia 2T racing bikes. The below schematic with calculations, offers his point of view with a simplified exhaust concept that will give some basic exhaust dimensions to start working on.
The SPJ carb from a later RS125 bike can be fitted on an earlier NF4 bike without much issues. The carb collar is a tight fit though removing the carb from the frame looks to be much easier than the stock PJ due to the shorter body. The throttle cable fitment clears the frame nicely as well. Most probably just the fitment of the carb without a proper electronic conversion from later bikes doesn't worth the hassle and the cost but it can still be used nonetheless.
Pickit is a family of programers for PIC microcontrollers, made by Microchip Technology. The latest version called PICkit3 features a 16-bit PIC24F processor and offers a useful & convenient way for either programming or debugging PIC and dsPIC microcontrollers. Accompanying the pickit3 and available for free download is a powerful graphical user interface called MPLAB Integrated Development Enviroment (IDE). For the connection to the PC you only need a free USB port and the pickit can be connected to the target via a header and instantly used as an in circuit serial programming (ICSP) device. Making a simple Google search for motorcycle projects using PIC microcontrollers, you will find lots of stuff like CDI units, Quick Shifters, Shift Lights etc. and sometimes these projects include the HEX files so you're ready to program and experiment with some PICs with the help of Pickit3.