Technical brake help

i have a 34 with disc front and rear with a 7" single booster. brakes work fine. but when i press the pedal the motor reves up about 900 rpm. can not find any leaks any where.

 

You could have a vacuum leak in the booster, or your idle mixture isn't adjusted properly.

 

When stepping on the powered brakes changes the running characteristics it's a pretty safe bet to say that there's something wrong with the booster.

Disconnect it, plug it, and run the car to verify