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Unread 09-08-2011, 10:10 AM   #1
Ken4444
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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.

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Unread 09-08-2011, 11:35 AM   #2
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That's a good idea. Also, you might want to place two springs there in case one breaks. I drag race and the track insists on two springs for that reason, and it seems like a good one to do for all my vehicles. It's a spring within a spring.
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Unread 09-08-2011, 11:36 AM   #3
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I do have two springs (one inside the other), and they pull fairly hard which is probably why the bracket pulled out of place.
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Unread 09-08-2011, 01:11 PM   #4
80cj
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I would suggest that anytime you notice a problem like that, turn the engine off and investigate immediately even if it mean getting to work a few minutes late. Imagine if you had a AMC 360 power CJ and that happened.
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Unread 09-08-2011, 01:25 PM   #5
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Quote:
Originally Posted by 80cj View Post
I would suggest that anytime you notice a problem like that, turn the engine off and investigate immediately even if it mean getting to work a few minutes late. Imagine if you had a AMC 360 power CJ and that happened.
Agreed. Since I hadn't been under the hood changing anything, and it had driven fine the day before, I couldn't imagine anything being really broken.

The other thing that was going though my mind was that the outside air temperature was about 60* and really dry; a huge improvement from the string of humid, hot 95 to 100* days we've had for the last 3 months. Anyhow, I was thinking that the cool, dry air was possibly related. In retrospect that was totally foolish though.
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