Ok I searched this question and seems nobody is talking abount this.
I set up a acceleration system with bricks of "Servo Control Motion" being actaveted by an property whith number that is kind of a velocimeter. I push the accel button and it add to the property and subtract when not pressed. The higher the number of property activate the Stronger "Motion Actuator", (corrent have 10 motion actuators in sequence each stronger than de last)
I Got that problem when the character is in mid air, while accelerating he's falling very slowly, stop the motion and he will fall normaly. It was actualy occuring with the "simple motion actuator" in "linear velocity" so a read in the manual that the "servo controler" fixes that problem. I tested it alone and seemed to work fine while falling. but after that I put it in sequence to simulate acceleration of a cart the problem of the slow fall was back. I don't know if i changed other option in phisics of the character to be hapening this.
I cold set up an sensor to stop all te Motions actuator while he's in mid air, but it will stop the motion foward when he's falling, and i want to keep the foward velocity while in air.