mitovarna

Here is a video of the bike running, with my audio commentary concerning what is apparently a lean condition evidenced by the backfire you hear.  Like many things, the advice/suggestions to deal with the condition are often contradictory...

According to online forums, the backfire could be caused by a lean condition, or an exhaust leak.  Of course, timing could be the culprit, which is evidenced by the very hot headers even at idle.  However, many mx450 engines do this, so glowing headers do not necessarily mean a lean condition.  There is no exhaust leak in the pipe, but the slip fit by the muffler is somewhat suspect, but that shouldn't cause the backfire alone.  Finally, nonstandard pipe and carb is no help, so the baseline to start is nonexistent.  Since the advent of fuel injection, no one stocks carb parts, so pilot jets will need to be ordered (already on the way...)  The joys of building and fabricating!!!  I'll get it figured.  Over the winter I will likely drop the engine and do a full inspection -- valves, timing, filters, etc.  Will have lots of time to do it!