fazer 400

hi there i have tried most places and had no luck so this is my last resort, i have a 99' fazer 400 and ever since the heavy frost i have been experiencing an intermitant lack of power which is accompanied by a noise (like someone is putting their hand over the airfilter intake) along with irratic speedo readings. When this happens the bike will only rev to about 2000rpm thus i cannot get out of first gear and can only do about 10mph with the bike backfiring as well. Also if i put an indicator on the power comes and goes with the flashing of the indicator.(So this suggests electrical rather than carburattion) I have had the bike for 3.5 years now and this is the only fault i have had with it (it has always been A1 reliable). It has beeen suggested to me cdi box but then again it could be coil/s breaking down. CAN ANYONE PLEASE HELP MY BELOVED FAZER!!!!!!!!