I have a 91 yamaha fzr6 and I'm getting spark on the left and the right but not in the middle ones why is that?

Distributor cap, wires or rotor. There may be carbon traces in the cap.

Carefully examine the middle spark plug wire for cracks, which are allowing it to short out to ground. Replacing the wires will likely solve the problem.

Also check wire routing. Wires that are next in line in the fireing order should not run parallel right next to each other.