MC 2100 frustrated jet question -
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post #1 of 7 Old 06-10-2010, 09:35 PM Thread Starter
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1980 CJ7 
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MC 2100 frustrated jet question

I have installed a 1.08 venturi MC 2100 on my 258. I have it pretty well tuned in, but it still runs a bit rich. I have no. 48 jets in right now. I also think I have a vacuum leak somewhere, as my mixture screws are turned all the way in and it runs the best. My question is, after trying to remove the current jets, and boogering up the slots, (they are really tight), what is the best way to remove. Drill and easy out? Tell me you haven't ever used a flat bar and a pair of vice grips to work on something? If I can only get one out? is there a problem with having two different sizes installed? 1-46 and 1-48? It does run right now, so I'm close to saying, "if it's not broke, don't fix it", but the gas smell? Thanks...

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post #2 of 7 Old 06-11-2010, 04:41 AM
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Originally Posted by engchase View Post
I also think I have a vacuum leak somewhere, as my mixture screws are turned all the way in and it runs the best
You need to get that problem fixed first. Those mixture screws should be out at least about 1 1/2 turns. Until you find your leak you'll never get it right.

I have the same carb on my 258 - 1.08 w/48 jets (air/fuel mix runs best at 2 3/4 turns out). It runs a little on the rich side - but that is where it runs best - and that is with the system Nuttered with the Team Rush upgrade and a MSD 6A box.

Trying to solve your rich problem by changing the jets (and yes they need to be the same) while you have a huge vacuum leak is the wrong way to go about it. Find the leak and everything else should sort itself out.

No matter where you go, there you are.
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post #3 of 7 Old 06-11-2010, 07:08 AM
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Check for blown power valve. It will cause the idle mixture srew adjustment problems and the rich mixture .
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post #4 of 7 Old 06-11-2010, 01:36 PM
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Get the largest flat head screwdriver you can find that will fit in the slot on the jet, stick it on top of that stuck jet, and rap on the end of it of the screwdriver handle with a hammer. Don't get too carried away or you'll crack the carb housing, but I did that with some stuck jets and got them out that way. I'm running 47's and am going to try 46's next to see how they do. Mine are close enough with the 47's, but a hair on the stinky side sometimes so I'm gonna try the 46's and see how they do.

85 CJ7 258, borla header, Team Rush, MC2100 ,optima batt, Warn 8274, agr super box 2 & pump, T5 w/ B&M shifter, centerforce 2, superior 1 piece axles, warn hubs 2.5 in lift, 31" BFG MT

85 CJ7 258, A/C, T176, MC2100, Team Rush, Warn XD8000i, superwinch hubs, 3in lift 31" BFG AT/KO
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post #5 of 7 Old 06-11-2010, 02:37 PM
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Sounds like a blown PV could be your issue. If you had a backfire or your jeep disealed recently then I would suspect it blew the PV. If you pull the cap that houses the PV and there is gas in it then it needs to be changed.

As for the jets, 48's were slightly big for me and eventually had to goto 47's. 46's ran my jeep way to lean however. They both need to be the same size. As mentioned before if you take a large flathead screw driver and tap the end of it as you slowly rotate the jet they should eventually work themselves loose. You can get new jets here but they can be pricey once shipping is added in:

Ford Motorcraft 2100 2150 2V Parts Page

The PV is just a standard flow holley PV. If you have trouble finding the replacement 2 stage from the rebuild kit then you can use a holley PV. I believe the walker 2 stage PV is p/n 7029. Around here it will run around 20 dollars once shipping etc is added in. Hope that helps, and goodluck!
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post #6 of 7 Old 06-11-2010, 08:31 PM Thread Starter
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I replaced the power valve recently, and it hasn't backfired since. I have considered the PV, and may need to check it again. I really think the possible vacuum leak is part of the problem, I just can't find it unless it is on the underside of the intake manifold. Believe me, I have sprayed a couple of cans of brake cleaner trying to find it.

I want to put the new jets in to see if it helps. I just want to hit the main problem rather than treat the symptoms.............

Here is where I got my replacement jets. (that I don't have installed yet)

The price is for a pair of jets. Shipping is very quick.

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post #7 of 7 Old 06-11-2010, 10:14 PM
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Pick up a small propane bottle from your local hardware store (under $10). Crack the nozzle and move it around the carb, intake, etc. Be sure to check the base/adapter gasket. It works, IMO, better than a spray. Is the choke still attached to the side of the carb? If not, there is a hole there that needs to be plugged.

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