MC2100 Carb tuning - JeepForum.com
 
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post #1 of 8 Old 01-14-2009, 08:42 PM Thread Starter
Kwish
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1982 CJ7 
 
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MC2100 Carb tuning

Well, I installed a MC2100 carb on my 4.2L last spring, and it seems to be running quite rich. Atleast Im guessing its rich from the massive backfires haha. Anyways, if anyone has tuned a MC2100 could anyone either help me with some pictures, or telling me which screw to turn? I have only found the screw to adjust the idle.

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post #2 of 8 Old 01-15-2009, 08:56 AM
kavephish
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There are two screws for idle mixture adjustment on the MC2100, both on the front/bottom of the carb. Make sure they are both turned out the same amount from bottom (ie. turn them all the way in till they TOUCH, not HIT, bottom, then back them out two turns to start) Hook a vacuum guage up to manifold vacuum and start your engine. You are looking for 18-21Hg CONSTANT on the vacuum guage. Turn one screw, then the other, bit by bit, until you reach maximum attainable vacuum on the guage. VERIFY your timing is correct. If this does not help you may have to rebuild your carb. Kits are cheap and easy to install - other than the float/needle and spring, there are no little parts that will go flying out if you open it up and shake it around - very easy rebuild. You may have also blown the power valve on the front/bottom of the carb (looks like a little 1 inch bowl). You will have to pull the carb off to check it. Take out the 4 screws holding it on....if there is gas in the 'bowl',the valve is bad. The valve will come with a rebuild kit, or you can purchase it seperately.
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post #3 of 8 Old 01-15-2009, 11:04 AM Thread Starter
Kwish
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Ah, alright thanks alot! now all I need is a vacuum gauge
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post #4 of 8 Old 07-03-2009, 10:43 PM
oldskull44
 
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motorcraft 2100 power valve question on 304

Quote:
Originally Posted by kavephish View Post
There are two screws for idle mixture adjustment on the MC2100, both on the front/bottom of the carb. Make sure they are both turned out the same amount from bottom (ie. turn them all the way in till they TOUCH, not HIT, bottom, then back them out two turns to start) Hook a vacuum guage up to manifold vacuum and start your engine. You are looking for 18-21Hg CONSTANT on the vacuum guage. Turn one screw, then the other, bit by bit, until you reach maximum attainable vacuum on the guage. VERIFY your timing is correct. If this does not help you may have to rebuild your carb. Kits are cheap and easy to install - other than the float/needle and spring, there are no little parts that will go flying out if you open it up and shake it around - very easy rebuild. You may have also blown the power valve on the front/bottom of the carb (looks like a little 1 inch bowl). You will have to pull the carb off to check it. Take out the 4 screws holding it on....if there is gas in the 'bowl',the valve is bad. The valve will come with a rebuild kit, or you can purchase it seperately.
I have a question regarding my carb on an 80 jeep with a 304. all stock.

I have problems with it running rough. sometimes it barely runs and it seems to change every time I hit a bump. I just got a rebuilt carb and I was told the electrical system is okay (it was put on a scope). I checked for vacuum leaks with carb cleaner at the base of the carb.

I was wondering if a back fire would blow the power valve and cause this problem. Or is there a different sympton of a blown power valve?
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post #5 of 8 Old 06-12-2019, 10:20 PM
swanny88
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I know this is an older post but it has some great information.

I am trying to fine tune my 258 that has a Clifford intake and a mc2100 carb. Have a variety of jets available as well. When I hook up my vacuum gauge to the intake manifold I noticed the needle bounces rather than remaining steady. The movement is not large, it just bounces about 3*. I suspect I may have an intake leak but when I spray fluid around it the engine doesn’t seem to change. My idle is somewhat rough as well. What things should I look for?

Swanny
1983 CJ 7, 258, 3 speed auto
Colorado
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post #6 of 8 Old 06-12-2019, 11:35 PM
OrangeCJ-5
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Is it doing one of these things?
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post #7 of 8 Old 06-13-2019, 01:57 AM
Matt1981CJ7
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Quote:
Originally Posted by swanny88 View Post
I know this is an older post but it has some great information.

I am trying to fine tune my 258 that has a Clifford intake and a mc2100 carb. Have a variety of jets available as well. When I hook up my vacuum gauge to the intake manifold I noticed the needle bounces rather than remaining steady. The movement is not large, it just bounces about 3*. I suspect I may have an intake leak but when I spray fluid around it the engine doesn’t seem to change. My idle is somewhat rough as well. What things should I look for?

Does it just bounce at idle, or does it bounce at all RPMs?

Matt


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post #8 of 8 Old 06-13-2019, 09:00 PM
swanny88
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Thanks guys it bounces at all rpms. The engine was fully rebuilt about 1 Year ago with new rings pistons, etc. I wonder if it’s my gauge.

Swanny
1983 CJ 7, 258, 3 speed auto
Colorado
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