Motorcycle Repair: tune up etc, unforseen circumstances, simple tune

Question
I have an 84 Magna waith 17000 miles.  the last time I took it out it ram great until the last hundred or so miles then it staeted running like crap.  WEhen I got it home  I removed the plugs ( plugs new when started)) two on the front were kinda black but not fouled. Due to unforseen circumstances I have not been able to get out since then.  I guess my question how often should the carb and the valves be adjusted and would this make any differance, if it happened all of a sudden?  I might add that  when I did take it out I sorta had to feather the throttle, if I tried to twist the throttle all of the way if fell on its face and I had to baby it slowley to get any power then it seemed to be ok, but still with the same [problem when I syopped and took off again.  I am going on a trip and don't whant any problems.

Answer
I tune mine up about once a year.  I check the valves, sync carbs change plugs, oil and filters.  This is probably and over kill but I hate to have a problem the road and it's relatively cheap insurance.  Your problem doesn't sound like a simple tune up problem.  With out being able to check anything, I'd recommend you look at the ignition modules or coils.  It sound like the bike has lost spark to the front cylinders.

Regards,
Rich