Sup guys Here I am with another question, I'm using my cougar now and I wanted to make a burnout of curiosity. but when I step on the brakes and then the gas It does not stay. It slowly moves foward. I will bleed the brakes for this but if this does not solve the problem, what else can it be? The booster? What!    

You could try backing the rear brake drum adjustment off slightly. Be careful though, for every little bit it is backed off the drum the lower the brake petal will go before the brakes really apply.  

Are your front brakes disc or drum?  If drum the fronts may need some tightening as well.  If you over tighten them though you run the risk of over heating the brakes and severely reducing your braking power.  It's a whole system so everything has to be balanced to be safe and keep things from failing.

My Thunderbird has a tough time too. I often wonder if it's the C6 trans because my Centurion in dense air and a little lite on the brake will start below 1500rpm.  

Put the nose up against a parked import and floor it!  Or you can try backing off the brake pedal, after flooring the gas, until the tires start spinning.  I carry a lot of weight in the back of my car so sometimes i have to floor it, let off the brake to let the car lurch forward and then hit the brake again.

And if all else fails get out the oil pour some in front of the tires, and let 'er rip.  

As much as I like the import idea, you'd have to wash your car afterwards :/