I just spent this weekend installing an MSD box on my 85 GMC 350c.i. I replaced the coil, cap and rotor and added the MSD all in one day. It feels like with the MSD it idles a little faster and it vibrates a little more. I can hear a couple hard bumps every now and then in my exhaust. I can definately see a little bit of performance increase but this faster sounding idle bothers me a little bit. I didnt change the plugs and they havent been changed in awhile do you think they could be my problem or is this just a normal thing after installing the MSD box? Its a 6A box so supposedly it puts out 6 sparks for every 1 I used to get.