I have the 258 with the Carter BBl and I too was having it die at idel and any time I used the clutch! I first changed the fuel and air filters (was time anyways). Found that this did not fix the problem so I shot some wd40 around the vacume lines and found no change in motor noise (rpm). So I decided to remove the carb for a rebuild/cleaning.
NOTE :I am not a master mechanic but a brave weekend wrencher.
I followed the limited info in my hayes manual as well as looking up the carb link listed above. I tore apart the carb and soaked the mid section with the float bowls and used spray cleaner on the rest of the carb. I followed the drill out instructions for the idle pickup tubes and reassembled the carb. While I had the carb off, I tightend the manifold bolts (had a leak near the fire wall). replased all the parts and fired up the ole-Jeep. after a small warm-up she runs better than ever.
I found the info in the carb ling to be of great value and well written.... THANKS>