78 CJ5 MC2100 Vacuum - JeepForum.com
 
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post #1 of 10 Old 06-01-2020, 10:09 PM Thread Starter
DeltaJeep38732
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78 CJ5 MC2100 Vacuum

New here but not new.. had an account that I cannot get into from my old email as the recovery email won’t come through.

About the jeep because I figure out how to fill out my profile:

78 CJ5 that I’ve had for 6 years or so with a 258 that according to research is either a 78 model or an 82 model based on the “plate” in front of distributor. MC2100 carb using the eBay adapter plate. Everything else is basically “stock” (no other mods).


Rebuild (new pistons, rings, crank turned, etc.) happened over the winter and the ole girl is running like a top, except for one issue: it would appear I’ve got some blow-by (oil leak from dipstick), which was the whole point of the rebuild in the first place 🏼 .

I’m trying to find out where I should connect my PCV to vacuum, as all the diagrams I find show a port in the center of the carb on back side at the base, and my MC2100 does not have a port there. Instead, there is a port on a 45 on back side closest to valve cover. Is this where I connect my PCV? What about the larger side of the PCV? Where does it go? I’ve been reading that was emissions stuff that I don’t have anymore, but want some clarity as all the diagrams I can find point me to a port that does not exist on my Jeep.

My hope is that pulling this vacuum through the PCV will alleviate my blow-by problem and we can move on.

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post #2 of 10 Old 06-01-2020, 10:33 PM
LJameson
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The port you are looking at is for the choke pull-off. It sounds like you got an earlier mc2100 that doesn't have a PCV port. Instead, those older carbs had a spacer between the carb and the intake manifold that had a port tapped into it for PCV. And since you're PCV is not hooked up, I can almost guarantee your blow-by problem is caused by that.




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post #3 of 10 Old 06-02-2020, 12:07 AM Thread Starter
DeltaJeep38732
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Quote:
Originally Posted by LJameson View Post
The port you are looking at is for the choke pull-off. It sounds like you got an earlier mc2100 that doesn't have a PCV port. Instead, those older carbs had a spacer between the carb and the intake manifold that had a port tapped into it for PCV. And since you're PCV is not hooked up, I can almost guarantee your blow-by problem is caused by that.



This is exactly where all the diagrams show a port that I do not have. Is this spacer a common thing that I’d be able to pick up at a parts house or more like a junkyard find?

ETA: I have a port on the rear of the manifold that currently has a plug in it. Could I put a hose barb there and connect to it? My understanding is PCV needs manifold vacuum vs the ported vacuum used for timing advance. This might not even be a source but thought I’d mention it just in case.

Last edited by DeltaJeep38732; 06-02-2020 at 12:30 AM. Reason: Added Info
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post #4 of 10 Old 06-02-2020, 08:53 AM
Matt1981CJ7
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I wouldn't use the manifold vacuum port on the #6 intake runner for the PCV. That would suck all the dirty blow-by gases into just one cylinder, instead spreading it out over all 6 cylinders. That could cause excessive carbon buildup in #6.

I would get the base plate adapter, like the one pictured above, and hook your PCV up properly.

Matt


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post #5 of 10 Old 06-02-2020, 10:41 AM
Hurricane4
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Will this work?

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post #6 of 10 Old 06-02-2020, 11:08 AM
LJameson
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Quote:
Originally Posted by Hurricane4 View Post

That looks like the part. I know a lot of older Ford small blocks that had a 2100 used the spacer.

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post #7 of 10 Old 06-02-2020, 11:13 AM
Hurricane4
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Agreed. Almost looks identical. Kind of pricey at $40.00. I remember when you could almost buy a new 2-barrel Jeep carb for that.

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"Success is not final. Failure is not fatal. It is the courage to continue that counts"
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Jeeps I Have Owned in Year Order:
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post #8 of 10 Old 06-02-2020, 11:56 AM
oldschool74cj5
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hello
here a little late but i can tell you what i have done in the past. if you have taken your egr off. then you simply add a tread inthe block off plate. installing a fitting to the upper port where the egr was. that will distribute the stuff from the pcv to all the cylinders. since i still have manual brakes i just used the port for where the vacuum fitting os for the brakes on the aluminum 2 barrel manifold.

oldschool
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post #9 of 10 Old 06-02-2020, 09:07 PM Thread Starter
DeltaJeep38732
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So, I’ve got the plate/spacer ordered, may be here by the weekend but not counting on it. I’ve asked this question to ehrmannamp and I’ve gotten no response so far, seems typical in my past communications with him. Will I need longer bolts to go from carb to my adapter plate?
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post #10 of 10 Old 06-07-2020, 01:34 PM
Mister4x4
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I guess I went a little weird with mine. The MC2100 on mine is from a '60s Mustang or Falcon (my pal hooked me up), and I used a Mr. Gasket adapter (no PCV port, like on the pics above). My PCV is hooked up to a port on the intake. Mine's a 1980 with a stock 1bbl intake.
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