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4.2 Starts cold dies as butterfly opens ??

920 views 8 replies 5 participants last post by  mickcollinsb16b 
#1 ·
I got this YJ as a project for my grandson. Have done some work (timing chain, ford ignition, intake manifold, vacuum lines, Alt, and radiator). After I got it back together it started right up but was rough. As the butterfly opened it smoothed out, still at high idle, and then stumbled and died when fully opened at lower idle. Have tried it again and same thing.
It acts like a vacuum leak but I have not found one "yet". On the other hand, when it starts cold, it seems rich. Could it be the metering pins or something I overlooked?
Not sure where to start so any help would be appreciated.
 
#5 ·
I had already double checked all the vacuum lines and replaced a couple of bad ones. That doesn't mean I didn't miss something. Been cold so not much done but I plan to check them once more and try disconnecting them one by one at the carb. I also want to check that the stepper motor and metering pins are working.
 
#6 ·
I lost all my old files, but someone on here should remember there is a great write up on these carbs and how to clean the top part where the gas goes in when at idle. Look down in the Carb. while it's running and see if the gas is dribbling out of the two ventures in the top part of the carb., if so that is the part that gets clogged up and will keep it for idling correctly. Good Luck and hopefully someone will come through with that write up on this 4.2s..
 
#8 ·
Thanks this is very good , but the main one I was thinking of goes into cleaning just the nozzles in the top part of the carb., but this is a great wright up on a complete rebuild.
 
#9 ·
If you are gonna dive into the rebuild of the original stepper carb I seriously recommend locating the OEM MOPAR rebuild kit. I found one in Iowa in Aug of 2013. It has the ever critical instructions. There are almost 80 pieces to the carb and highly recommend. You can find it still. I ended up finding 2 other dealers (1 was in Nebraska and Kentucky I believe). Just call your local dealer and they can do a nationwide search and give you a couple of leads and start there. My instructions were lost when I moved otherwise I would send them to you. I had a Ca Jeep as well. Never got it to run very well and went ahead and started converting it to MPI.
 
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