A warning about an odd problem
So I fired up the 258 this morning to drive to work, and right away I noticed the accelerator pedal was really sensitive. My first thought was that the floor mat was hung up, but it was not.
I ended up taking off my shoes so that I could get a better feel for the pedal. That helped me drive better, but there was still a problem somewhere. I was using my toes to press the pedal; it was that sensitive. It almost felt like the throttle wasn't snapping back to the idle position quickly.
So I'm driving to work and started to wonder if it was even safe to drive. It was a short 4 mile trip on slow roads, so I kept driving. All I could think was, "What is the heck has crapped out now?"
The one thing I knew was that I had NOT changed anything under the hood the day before, so that make the problem even more of a mystery.
I got to work OK, popped the hood, and looked at the MC2150. Right away I saw the problem: The bracket that holds the throttle return springs had gotten loose, pivoted around, and the springs were not pulling against the throttle mechanism. They were basically slack.
As far as I can tell it was only the weight of the factory throttle linkage assembly (metal brackets and a metal shaft) was the only thing pulling the throttle closed.
So, this exposes a major flaw in the usual method that people use for the MC2100 conversion: The throttle return springs connect to a bracket that's only held in place by one bolt (one of the bolts used to connect the carb to the adapter plate). Ideally, the bracket should be held down by 2 bolts so that if they get loose, the bracket doesn't move out of position, and your throttle will still snap to the closed position when you let off the pedal.
I always worried about this design, but figured that if I tightened the bolt enough then it would hold OK.
Time to fabricate a proper bracket for the throttle return springs.
"I give you a republic, if you can keep it." - Benjamin Franklin