bikeracer

You need the bars so the bike doesn't fall on its side when cornering,but those bars are ridiculous,they need to be shorter and sticking straight out.
The previous owner was probably trying to steer it like a car,it's the opposite for a bike,the front wheel needs to turn opposite to the steering input to make the bike lean into the corner.
Just stand the bike upright and see what happens when you move the steering,the bike needs to fall sideways in the same direction as the steering input.If it doesn't reverse the steering on the TX.Those bars at the moment will not let the bike lean.

You don't need reverse on a bike.

Suggest you scrap that existing steering linkage and just use one long rod through the servo arm pivot with a spring on each side and a collet to hold them in place at each end.You need to be able to hold the bike on its side and the front wheel should flop to one side without moving the servo.you can always tighten the springs for more steering as you get used to it.
The existing steering looks too much like a direct link and you'll never control the bike like that.

.