How to adjust choke on MC2100? - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep CJ Forum > How to adjust choke on MC2100?

Eliminate Hood Flutter!!!Thursday Savings BlastIntroducing MONSTALINERô UV Permanent DIY Roll On Bed Line

Reply
Unread 04-24-2013, 05:33 PM   #1
sarfu
Registered User
1974 CJ5 
 
Join Date: Aug 2011
Location: Point Pleasant, NJ
Posts: 236
How to adjust choke on MC2100?

Hi Guys,

I have a newly rebuilt Mc2100 carb on my 304, V8 and everything is fine except when I start it for the first time of the day.
It starts fine but then idles rough for 1 to 2 minutes before the fast idle kicks in, after that it is fine and runs beautifully all day, it is just that first cold start that I have this annoying rough idle, so where should my choke be?


sarfu is offline   Reply With Quote Quick reply to this message
Unread 04-24-2013, 06:54 PM   #2
Matt1981CJ7
Web Wheeler
 
Matt1981CJ7's Avatar
1981 CJ7 
 
Join Date: May 2011
Location: Elbert, CO
Posts: 10,468
Are you setting the choke by flooring the throttle before you start? Do the choke flaps close completely when you do so?

If so, hooking your distributor up to manifold vac, if it's not already, will drastically improve cold starts.

Matt
Matt1981CJ7 is offline   Reply With Quote Quick reply to this message
Unread 04-24-2013, 07:33 PM   #3
sarfu
Registered User
1974 CJ5 
 
Join Date: Aug 2011
Location: Point Pleasant, NJ
Posts: 236
Yes, pushing throttle to the floor once, and yes choke flap closes completely, she starts right up runs fine for a few seconds and then starts to idle rough for a couple minutes like she is not getting enough gas.
Brand new fuel pump, fuel filter and hoses, also replaced all my vac hoses with new and made sure all was nice and tight, re-torqued the carb to manifold bolts, no vac leaks that I can find.
She runs awesome after this initial couple minutes.

My distributor vac hose is hooked up to a cto switch on the thermostat housing where it has always been.
I did not have this issue with my old mc2100 carb, only after the rebuild.
sarfu is offline   Reply With Quote Quick reply to this message
Unread 04-24-2013, 09:29 PM   #4
86cj74.2L
Web Wheeler
 
86cj74.2L's Avatar
2004 WJ 
 
Join Date: Jul 2006
Location: Stouchsburg, PA
Posts: 6,759
When its first started and starts to run rough crack open the choke plate a little farther and see if it smooths out. It most likely will. Which means choke is too aggressive.

If it gets worse opening choke a little more then its not tight enough.
86cj74.2L is offline   Reply With Quote Quick reply to this message
Unread 04-24-2013, 09:44 PM   #5
jeepdaddy2000
Registered User
1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point Oregon
Posts: 6,237
Quote:
Originally Posted by 86cj74.2L View Post
When its first started and starts to run rough crack open the choke plate a little farther and see if it smooths out. It most likely will. Which means choke is too aggressive.

If it gets worse opening choke a little more then its not tight enough.
X2
Most MC carbs have a choke pull off, either internal or external. these are adjustable. Most carbs are set in the 3/16ths range with the engine running and cold. You can check by using a drill bit (don't drop it!) to measure the opening.
jeepdaddy2000 is offline   Reply With Quote Quick reply to this message
Unread 04-25-2013, 12:06 AM   #6
86cj74.2L
Web Wheeler
 
86cj74.2L's Avatar
2004 WJ 
 
Join Date: Jul 2006
Location: Stouchsburg, PA
Posts: 6,759
Same with the BBD. The choke plate snaps completely shut when its set. And as soon as the engine starts the choke pullback (which is operated by manifold vacuum) opens it up .095.
86cj74.2L is offline   Reply With Quote Quick reply to this message
Unread 04-25-2013, 08:05 AM   #7
sarfu
Registered User
1974 CJ5 
 
Join Date: Aug 2011
Location: Point Pleasant, NJ
Posts: 236
To adjust the choke plate opening do I turn the screw on the high idle cam and it needs to be on the second step down correct?
sarfu is offline   Reply With Quote Quick reply to this message
Unread 04-25-2013, 01:15 PM   #8
86cj74.2L
Web Wheeler
 
86cj74.2L's Avatar
2004 WJ 
 
Join Date: Jul 2006
Location: Stouchsburg, PA
Posts: 6,759
Quote:
Originally Posted by sarfu
To adjust the choke plate opening do I turn the screw on the high idle cam and it needs to be on the second step down correct?
One of the motorcraft users will need to answer that question.
86cj74.2L is offline   Reply With Quote Quick reply to this message
Unread 04-25-2013, 03:28 PM   #9
jeepdaddy2000
Registered User
1971 CJ5 
 
Join Date: Jan 2002
Location: Eagle Point Oregon
Posts: 6,237
The choke plate opening (or duration) is adjusted by rotating the black cap on the side of the carb. You will need to loosen the three screws (or drill out the rivets on later models) in ordeer to rotate it. The easiest way to set the choke is to run a garden hose on the choke housing, using the water to cool it. I like to set mine so the plate lightly snaps shut when I tap it with my finger in the closed position.

The choke pull off is a piston inside the housing(early models), a set screw on the top of the airhorn (intermediate), or an external vacuum motor on the side of the carb (late), usually behind the choke housing.
Early models weren't adjustable. The intermediates are adjusted by rotating the screw in or out to get the desired gap. Late models are adjusted by bending the linkage.
Start the engine and measure the gap between the plate and the side of the carb. Distances vary, but 3/16ths is a good place to start.

Once these adjustments are done, you can adjust your high idle. This is done using a screw that sets on a cam. High idle settings vary by model, altitude, and transmission type. I usually run mine in the 700RPM zone (manual trans), with it dropping off to a preset 500RPM's at idle with the cam disengaged. Colder weather may require a higher idle.
The steps on the cam are adjustable by bending the linkage rod.

Make sure that when you are done, the choke is completely open and the high idle is disengages with the engine warm.

All of these adjujstments can be modified by you at any time. If you go out in the dead of an Alaskan winter and find the idle is too low (screw), choke comes off too quickly (low idle before the engine is warm enough) or won't completely open (black cover) when warm, or it runs lean/rich on initial startup (choke pull off), you can make the adjustment on the spot.
jeepdaddy2000 is offline   Reply With Quote Quick reply to this message
Unread 04-25-2013, 04:37 PM   #10
sarfu
Registered User
1974 CJ5 
 
Join Date: Aug 2011
Location: Point Pleasant, NJ
Posts: 236
Problem solved, I adjusted the fast idle cam screw to open the choke flap a little.

Thanks very much for the input, much appreciated.
sarfu is offline   Reply With Quote Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Thread Tools






Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.