If your timing is changing due to decoupling, there is something serious wrong.
I also agree with this.
To me... A 47uF cap on a power rail feed to a motor would discharge MUCH faster than you indicate with a motor as a load.
0.1uF Caps are all about really short spike/dip (aka noise) control. 47uF is about power rail smoothing... but from what you describe you would have needed to add a value closer to the thousands of uF not a relatively small 47uF. You can often find 47uF in the back end of regulator circuit to stabilize the regulator itself and it would technically not change how much stored voltage is available to your circuit much beyond your source voltage being removed. (IE, a period only measurable with a O-SCOPE, in my opinion)