I was poking around with the time machine again last night and I was able to determine that there has been some unauthorized meddling on the contraption. Every time the apparatus gets to working pretty good and building up some acceleration something happens causing the propulsion thrusters to reverse into the retro mode and slow the thing down. After analyzing the electronic servometer, I was able to determine that the controls had been reversed by a remote control bought at Radio Shack and operated out of the Federal Reserve headquarters in Washington, D.C.
Apparently Ben and the Feds don't want to acompany us back to 1974 and they are willing to keep throwing an occasional $200,000,000,000 at the banks to keep us from making the trip.
I will either have to develop an electronic device to jam the Feds remote or find some other way to get through the blizzard of money that they are flooding the atmosphere with.
I can not make a reliable prediction when we will get back to 1974 when I have to fight with an evil empire like the Fed. This is the moral equivalent of economic war.