Motorcycle Repair: spit, throttle position sensor, spilt second

Question
2001 h-d, Heritage fuel injection.
Last year it started to spit.  It does not do it all the time.  Only between the speeds of 45 and 57.  Faster then that and it never does it and it does not do it all the time.  Some time it will go for hours and never do it and then it may do it every few seconds. Changed plugs and throttle position sensor. No other changes have been made. No check engine light or anything.  It runs and idles great, will be running along and just miss for a spilt second.( I call it a spit)  Have run many tanks of gas through it since it started so I don't think its water in fuel, but don't know what else to try.  

Answer
I have a 98 fuel injected bike and it does it every once in a while. I have looked and looked and cannot find any reason for it. The only thing I can think of is the ignition is breaking down for a moment, but I have never replaced it due to the cost.
Sorry I couldnt be more help
Mike