[Shotimes] Lack of power??

[Shaun & Meggen Livermore]

I finally got the old beast back together! (heater core replacement)
She seems to run fine, but I've noticed that once in a while it starts
to lack power.  From a stop you press on the gas and she'll go, but
accelerate slowly.  She put, puts like she is going to die, and then a
few seconds later the power kicks in.  Forgive me if my explanation is
weak.  Any ideas of what is causing this?  And how to fix it.  Thanks!
 
Shaun
91 plus 128 K