Joe C,

After all my dumbass troubleshooting, I went ahead and followed the
instructions to clear the idle tubes. Forget sludge in the tubes, one
of them had a huge chunk of metal stuck in it! I pulled the chunk out,
put the carb back together, and it runs great! This was a rebuilt carb
fresh from the parts store!!

Note to others: From all the notes I could find, clogged idle tubes
were supposed to look like a rich condition. Not in this case! It ran
like it had a horrible vacuum leak.

Thanks!

-rev


Oh, and apparantly someone already invented the old model ignition
module in the new model engine - it's called the "Nutter Bypass" and
there are far easier ways to do it.




The Reverend Natural Light wrote:
> Greetings.
>
> I'm working on a 1990 Jeep YJ, 4.2L I6, that won't idle. From 1200RPM
> up, everything's fine. It runs smooth under power. It won't idle at
> all.
>
> The previous owner replaced the carb with an older non-computer
> controlled unit. He made the decision to use the older carb because it
> was cheaper and simpler and someone knowledgeable (?) told him to. I
> believe it never ran right while he owned it.
>
> I have:
>
> 1. Checked for vacuum leaks.
> 2. Made sure the EGR valve is completely closed.
> 3. Replaced spark plugs and checked cap and rotor (old plugs were worn
> but tan).
> 4. Verified functional vacuum advance function.
> 5. Verified electric choke function.
> 6. Tried various settings of the idle bleed screws. Currently 2 turns
> out.
>
> No help.
>
> Since it has an ECM controlling spark but no electronic carb, I figured
> the computer controlled spark could be an issue. So, I picked up a new
> spark control module for a non-ECM jeep and wired it up to the
> distributor following the wiring diagram for an older jeep. Now there
> is no computer control whatsoever.
>
> No help with idle, but the throttle response seems a bit crisper.
>
>
> It appears to be running lean at closed-throttle because it will idle
> if I manually close the choke flapper. This leads me to believe that
> the problem is not the common "idle tubes" issue which causes a rich
> condition. It really feels like a bad vacuum leak but I can't find it.
>
>
> I'm completely out of ideas. In all honesty, I'm a lot more
> comfortable working on fuel injection. A grizzled Jeep veteran could
> probably whack it with a hammer and it would purr like a kitten. Any
> advice?
>
> Thanks!
>
>
> -rev