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Discussion Starter · #1 ·
Is there a good source showing which vacuum lines can be removed? I don't care anything about smog, I just want to clean up the engine bay. I know there's the FSM, but something more direct on what to pull off?

'89,4.2, ax15, hei conversion, original carb.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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If you have and HEI and an aftermarket Carb a 4.2 without the PCM, Everything can go except the Dist advance, the 4wd vacuum to the Cad, the vacuum for the defroster vents and the lines to the charcoal canister.
If you still have the Stock carb and PCM I wouldn't touch a thing except to make sure they are all in good condition.
 

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You can do a Nutter bypass and keep the stock carburetor. As part of the Nutter bypass, you set the needles in the stepper motor and unplug the harness from the stepper. With the Nutter bypass, you can remove all the vacuum hoses, leaving only the ones that Got it at last mentions.
Google Nutter Bypass if you're interested in how it's done. Before you actually Nutter your Jeep, post here for a couple tips.

If you install a HEI distributor after doing the Nutter bypass, you've already set the needles in stepper motor on the carb.
I bought a re-man Carter BBD without a stepper motor to run with my HEI. In my opinion, that's the best setup if you don't have to pass emissions. I could probably pass emission testing because I keep my motor tuned up. If it wouldn't pass, it's probably from blowby rather than carb issues.

There's been some discussion about running distributor vacuum from a carb port or from the manifold. I found better results running my distributor vacuum from the manifold.

Good Luck, L.M.
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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There's been some discussion about running distributor vacuum from a carb port or from the manifold. I found better results running my distributor vacuum from the manifold.

Good Luck, L.M.
You Rebel You.....
Still haven't made the switch myself yet, But everything I've read points to that making more sense. It's most likely good advice, though the carb guy I bought my Motorcraft from included coming off the carb.
 

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You Rebel You.....
Still haven't made the switch myself yet, But everything I've read points to that making more sense. It's most likely good advice, though the carb guy I bought my Motorcraft from included coming off the carb.
Try each one. Probably the only practical way to tell the difference for us guys without sophisticated test equipment is with the good ol' seat of the pants dyno.
For me, if I didn't allow my old heap to warm up a bit before taking off, it would occasionally pop while accelerating from a shift until it warmed up. Not really a back fire, but a pop out the carb.
From time to time it would "run on" or "diesel" when I shut it off. Since going to manifold vacuum, it doesn't do it.

These old heaps all have a long and varied history. Some have been run hard and put away wet. Others have been run wet and put away hard. Meaning some have had a hard life, and others have had a hard life with little maintenance. Then there's always the Bubba factor.
At the age that YJs are (my build date is 4/11/1986) they can be anywhere from 33 years old to the youngest at 24 years old. Engine condition can be anywhere from a brand new professionally built long block to some rusty old pot that a farmer uses to pull his manure wagon and only adds oil when it begins to knock.
My engine is worn and will require replacement some time in the not too distant future. Plus, I live at 6500' altitude and it's difficult for even a new engine to develop vacuum. The best I can get on my vacuum gauge is 11 inches. At sea level this would be around 15 inches.

If a person is at sea level he might develop more vacuum and the ported vacuum could work better.

Here's an article that states ported vacuum is what we need to run to our distributors.

https://www.motor.com/magazine-summary/mastering-the-basics-reading-a-vacuum-gauge/

Another poster here presented a well written article stating to use manifold vacuum. Based on what the other poster posted, I tried both. My intuition was to run ported vacuum, but my tired old 4.2 seems to like manifold vacuum better. Maybe I should have simply retarded my timing a bit and kept the ported vacuum.

Now that I've really muddied the waters...…

Good Luck, L.M.
 

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Thanks Gottagofast for the Super Chevy link.
Now this thread has both sides of the discussion located in one handy place. We can keep track of this thread and the links so that when the discussion of ported vs manifold vacuum comes up again (it will) we can refer back to this thread.

Good Luck, L.M.
 

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Yeah riiiiiiight.... like we really won't forget where we posted this stuff.... lol

Maybe we need a nutter, vacuum advance, and other carby stuff sticky....
 

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I thought about starting a thread with a similar title earlier today.
It might be something like "YJ carburetor tips & tricks". Then posters can post their opinions and experiences with the OE Carter carbs, the MC2000 series carbs or a Weber carb.
From time to time I post a link about cleaning the idle tubes in a BBD carb. I have to go back to my paper YJ file and thumb through it to find the address of the link. It'd be handy to have it as a sticky.

I'll get on it as soon as I have some spare time. Hopefully in the next few days.

Good Luck, L.M.
 

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Discussion Starter · #10 ·
I thought the nutter was to bypass the old distributor. I see there is something about adjusting some needles on the carb as well. I've replaced the stock distributor with an HEI setup. Do I need to do any wiring then for the Nutter, or is it just some carb adjustments?
 

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The Nutter bypass instructions should have directions on how to manually set the stepper motor needles. With the stepper motor needles manually set, leave the plug to it disconnected.
With a HEI distributor installed and the stepper motor disconnected all the emissions controls are bypassed. Also, the PCM no longer has any function.

If I remember correctly, the Nutter bypass bypasses the PCM (computer) but allows the ECM (Engine Control Module) to continue functioning. The HEI bypasses both and puts the tune up technician (you) in control of, and responsible for, the timing and carb settings.
That's if I remember correctly.

Good Luck, L.M.
 

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If you have and HEI and an aftermarket Carb a 4.2 without the PCM, Everything can go except the Dist advance, the 4wd vacuum to the Cad, the vacuum for the defroster vents and the lines to the charcoal canister.
If you still have the Stock carb and PCM I wouldn't touch a thing except to make sure they are all in good condition.


I actually don’t have my canister hooked up either. I read debates on either side, and I don’t have a gas smell that some reported with it gone, so my OCD against clutter won out and I’ve kept it disconnected, getting rid of a few more lines.


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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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I actually don’t have my canister hooked up either. I read debates on either side, and I don’t have a gas smell that some reported with it gone, so my OCD against clutter won out and I’ve kept it disconnected, getting rid of a few more lines.


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I think with the CTO removed the cannister is basically useless at this point. I just never felt the urge to Remove it. Probably should have when I replaced the coolant tank a few weeks back. Nice to know it isn't necessary.
 

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I’ve read that some people get vapor smell without it. And I’m sure it somehow contributes to emissions, but the PO has all the lines crossed when I bought it and I just never put it back together. The actual canister is still there, but no lines attached. I HATE engine clutter, and I’m sure I’m going to pull something important one day. Haha.


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