Maybe add some kind of systematic way to diagnose problems like
Engine does not start/run well
- Engine needs compression, correct fuel/air ratio, and spark.
Compression. Use a screw in type compression gauge to verify each cylinder is within tolerance and within % of each other.
Air/Fuel.
- Is the engine runs, is it lean/rich (by reading plugs)?
- Are the carb boots on tight?
- Fresh gas (or at least stored with Stabil)?
- Is the carburetor clean (no clogged passages, main and pilot jet clean, air screw clean, no varnish)?
- Air screw adjusted properly?
- Is the needle valve functioning? Are the oil lines purged of air and the oil pump correctly pumping oil? Is the fuel pump pumping fuel? No cracks in the fuel lines?
- Inspect the reeds for damage.
- Exhaust leak around damaged donut? Missing springs
- Powervalves misadjusted, cable siezed or barrel pulled through the top of the valve?
Spark.
- Check by resting plug against cylinder bolt and turning over (or with a inline spark tester)
- TORS adjustment needed if the engine cuts immediately upon throttle and restores after release.
- Spark plug fouled? Spark plug caps corroded or resistor bad? Unscrew and test, should be 5k ohms.
- Wire rub through from vibration can cause intermittent spark loss. Bad spots are under the motor / by the water pump, near CDI box, by handlebars, under seat to rear.
- Bad connections at connectors. Clean terminals, use electrical grease during reinstallation
- Stator/Coils (poor starting and or poor running), run multimeter tests, swap out for a known good unit
- CDI - swap for a known good box
