MC 2100 - NON-smog vacuum line question -
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Unread 10-04-2010, 03:07 PM   #1
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1989 YJ Wrangler 
Join Date: Sep 2010
Location: Wenatchee, Washington
Posts: 32
MC 2100 - NON-smog vacuum line question

Well, I ordered an MC2100 from the guy on e-bay. I ordered the non-smog kit thinking I would get rid of as much junk under the hood as possible. The carb is on its way, but I found the instructions for his kit online:

On page 40, he gives instructions for vacuum lines. I also intend to do the nutter bypass. My concern is that if the new carb does NOT have ported manifold vacuum he says to just leave the vacuum line disconnected.

Question #1 - Anyone running without vacuum advance? How does it work?
Question #2 - Anyone running manifold vacuum with MC2100 and Nutter Bypass?

Should I send the carb back and get the smogger version?

Below is a pasted section of his instructions -

"Most distributors from this era have several simultaneous methods of advancing the
ignition timing. Base timing (the lowest amount of advance ever achieved) is usually set
around 8-12 degrees BTDC (14-18 high altitude). In addition to this, spring-loaded
centrifugal weights will further advance the timing (as much as a dozen or two degrees)
as the engine speeds up. The third and most complicated method is the vacuum advance.
There are several different methods that Jeep employed to implement the vacuum
advance feature, but it essentially works like this: A CTO (coolant temperature override)
switch uses engine coolant to sense when the engine has warmed up. When it's cold, the
distributor is advanced using manifold vacuum, so the ignition is advanced farther when
idling than it is under load. When the engine warms up, the distributor is advanced using
ported vacuum, so the ignition is advanced farther under load than it is at idle. MOST
Jeeps will NOT have this particular CTO switch and will run their vacuum advance
directly into “ported” vacuum. This will properly advance the spark at W.O.T. (wide
open throttle) and under highway speeds. You will lose the advance at start up, but with
the new carb, you will still be OK on the coldest of days."

makarov9mm is offline   Reply With Quote Quick reply to this message
Unread 06-30-2011, 05:05 PM   #2
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Join Date: Aug 2009
Location: Oklahoma
Posts: 15
I'm dealing with the same question. I installed the MC2100 via the same kit.

Moving away from the distributor the vacuum advance Ys in with another line and then to manifold vacuum.

Should I disconnect the Y and reroute the dizzy advance to a ported source?

The published diagrams don't seem to readily identify the source of the other branch of the Y. What should be done with this line?

Thanks in advance!
SoonerMed is offline   Reply With Quote Quick reply to this message
Unread 06-30-2011, 05:51 PM   #3
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1988 YJ Wrangler 
Join Date: Apr 2007
Location: Rio Rancho NM
Posts: 4,298
Keep your dizzy on manifold vacuum, here is why
You will also gain by using a pre smog dizzy, source
And this is the one I used

4.7stroker is offline   Reply With Quote Quick reply to this message
Unread 07-01-2011, 11:35 AM   #4
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Join Date: Aug 2009
Location: Oklahoma
Posts: 15
Thanks for the links, Dwayne. Looks like I'll need to wade into the ported vs manifold debate again.

Any insights into the line y'd in with the vacuum advance?

Thanks again.
SoonerMed is offline   Reply With Quote Quick reply to this message

bypass , carb , mc2100 , nutter , vacuum

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