I hope someone can help

I've built the gen 1 interrupter and have an issue with the output in fixed mode,the signal which is coming from the output (from Pin 4 of chip) is jumping a few us and does this regardless of the PW or Frequency pot position. I've checked my circuit and wiring I've programmed 2 different chips so 3 in total and all have the same problem.
here is a video link of my circuit: https://www.youtube.com/watch?v=KqAb0Yklx74
hope this helps
I'm not to good with Arduino code but can figure it out if i know what to look for so if someone can point me in the right direction i mite be able to fix this pw jumping issue.
also were in the code do i need to adjust to increase the frequency bps from 200Hz/300Hz to say 20Hz to 600Hz?
Thanks for your time and hopefully help

Simon, UK