Right I need to loose 3.3 stone to be on the race weight. I haven't got 3.3 stone of fat so how do you loose muscle?
I'm 104kg in race clothes and helmet and need to be 84.
Ive got a diet to loose fat and iv been body building for 4 years now. No matter what I do in the gym I always pump up which can't be good?
Iv been doing cv then very light weights and loads of reps, all non stop to keep the heart rate up.
Should I be cutting out the weights altogether?
Would love some weight loss tips 
I only know how to get big
You mention your weight. How much body fat are you carrying? Most people like to talk about how much weight they have but never mention how much fat % they have. This shows the muscle they really have.
It seems that you could possibly lose quite a bit of fat due to the fact that you say your strength has decreased recently. If you were a lean 100kg, this wouldnt neccessarily happen.
Just because you pump up, it doesn't mean you are getting and bigger, its mainly just a feeling that will subside after a few days.
Diet is the most important part of training. Control that, and you may get to your target (depending on many factors including genetics). But losing 20kg will take a while, so as mentioned earlier, you may do best to find another class of racing.