Sounds like you may be having a prob with it being too lean. You will be rich when you first fire it up ad the car will lean out when you run it and bring it up to temp.
What temp are you going to the starting line with? CHeck this and then check again after a five minute run.
If you are coming off hot and idling high (after your run) but you are going on the starting line at reasonable temps and idle level, then you might have an air leak. Now if you do not leak or go hot all of the time but you do after your tank goes down to a certain level, it may be your tank.
Try fueling your tank and let the motor continue running when you think it is idling high. If the idle goes down then you know.
Pressure lines can do this as well. When in doubt....change the lines.
Let us know what you find.