Okay, the hint is that I had just gotten through working with the throttle switch and linkage. Also, when I pressed on the accelerator, the engine did not rev, indicating a broken linkage somewhere to the throttle. In this case, the plastic housing on the throttle linkage was so brittle that I had previously snapped off the hold-down clamp (Figure 1) while working on the throttle switch. I thought that I could get away with just snapping the plastic socket of the link end onto the metal ball of the throttle without using the plastic hold-down clamp. Wrong! The cupped end of the link would not stay on the ball when the throttle was rotated. I ran back home and got some wire and wired the plastic housing around the ball (Figure 2) so that the linkage would not slip off, and then drove home. Later, I got a spare throttle linkage (one with a good plastic hold-down clamp) from the junkyard.

Figure 1. This is a throttle end link with a good
functioning hold-down clamp.
Figure 2. The temporary fix was wire wrapped
around the plastic end link to hold it onto the metal
ball of throttle.