1990 wrangler 4.2 Vac lines. Bringing her back from the dead - Jeep Wrangler Forum
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Old 09-28-2018, 02:44 AM
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1990 wrangler 4.2 Vac lines. Bringing her back from the dead

So I was able to acquire my first Jeep, was told it was going to go to scrap, decided from the previous owner to let me keep it. Got it back to the house, found it has a few issues but my main concern is to get the engine running. Been sitting in a field for a few years, it’s in rough shape l. Flushed the fuel out, new fuel, could tell the carb was gummy. Rebuilt carb. Have seen most people have a Webber but this is a Holley, not sure if that was a previous upgrade that people has done. I’ve got it to idle after warmed up, pretty sure the choke isn’t working correctly, any advise on that would be appreciated, but after looking at the vacuum lines that have been pieced together (looks like someone didn’t have enough so the pieced everything together). A lot of lines were off and kinda guessed where they went, it ran somewhat decent so I think I’ve got it close. Questions are: Is the nutter delete acceptable for the Holley carb? Can I delete most of the lines, I saw the front diff has the lines running to it and have found the linkage upgrade so I’ll be going with that to remove a few more. On top of the valve cover has a block, one main line with looks to be 3 tees and a handful of wires coming off of it. Not a clue what’s that for. Again, new to the Jeep world. Any advice would be greatly appreciated, I’m sure I’ll have a few more questions to come. Thanks

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Old 09-28-2018, 03:56 PM   #2
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I ran an old Ford Holley on mine for a while. This was a long time ago so I certainly don't remember the specifics, but I did get rid of most of the vacuum stuff. A lot of it went to emissions stuff. If you need emission testing in your area then you will need to make it all work as it was designed. If you don't, get rid of as much as you can. You will need vacuum to the distributer and the 4wd. That's about it. The 4wd is a little complicated. the vacuum runs to the t-case and to the front axle. There is a storage ball under the battery and a few filter type things. Maybe they are regulators of some sort. You mentioned a Posi Lock or something similar. That would eliminate all this stuff so not a bad way to go. Make sure you get some vacuum caps to plug any spare ports on the carb.

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Old 09-28-2018, 04:43 PM
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Luckily I don’t have emissions here in VA, I’ll do the posi lock just to get rid of the vac lines to help clean it up and wasn’t 100% what is needed beside the carb and vacuum advance, PVC, intake. Dose the transfer case need it or is that only to engage the front axle?
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Old 09-28-2018, 06:02 PM   #4
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I don't care for Posi Lock, but in your particular situation, it might be the way to go.
On a stock setup, the vacuum lines run to a switch on the transfer case. When the TC is shifted into 4X, the switch sends vacuum to the front axle to engage a collar that puts the front axle into 4X.
With the Posi Lock, you don't need any vacuum to the TC.

I suggest you look into a Nutter bypass or a HEI distributor.
The Nutter bypass is close to free. My HEI distributor was $150.00 plus the cost of a relay, some wire and a few terminals. In my opinion, the HEI distributor is the way to go if you don't have emission testing.
With the HEI distributor, you eliminate the computer (PCM) , all the emission controls and the ignition control module (ICM). You can discard all the vacuum lines except the one to the power brake booster and the one to the distributor. I left a vacuum line to my charcoal canister to pull fumes into my engine, rather than allow the fumes to pollute the atmosphere.
Most folks that are running a HEI agree that the Jeep runs better with the HEI.

For more assistance, you can Google:
Nutter Bypass
HEI distributor
YJ vacuum system for transfer case
MC 2100 carburetor
MC 2150 carburetor

The stock carb on a YJ 4.2 is a Carter BBD. A Motocraft or Holly carb was and is a common upgrade. The MC (Motocraft) carbs seem to be less finicky than the Webers.

Other posters that are running Hollys or MC carbs should chime in with the difference and their opinions.
I'm unfamiliar with those carbs, but I kinda-sorta think they're related.

Good Luck, L.M.
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