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Unread 05-18-2012, 07:44 PM   #1
orengutan
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new MC2100: no idle

Hey folks,

so I've picked up a MC2100 no smog unit from the ebay guy. it came in a nice box with seemingly everything I needed: awesome!

from the instructions and emails, I understood that it comes pre-tuned with what should be the right idle settings, so I avoided touching those screws for now.

I installed the carb, plugged everything that needs to be plugged (pulse air activator valves, moved PCV to a T on the manifold), did the nutter (dist to starter, etc).

Unfortunately, I still can't get the jeep to idle. I've blindly adjusted the dist timing, assuming that I can get it close enough to a running stage and then use the light to set the timing, but I can't get any idling.

I can get the jeep started by flooring the pedal though. it'll run, very unevenly, and as soon as I stop gassing, it dies.

I re-installed the carb, thinking maybe I have a leak in one of the seals (used RTV this time), but nothing. same problem.

so, I have some guesses based on theory, but I dont know how to check these things:

1. not enough fuel on idle? it does run when I floor itů the unevenness of that running might be due to misadjusted timing?

2. something is still leaking air. somewhere. it's not the carb seating though.

3. I have a manual choke now. I dont know if that would affect this. I've tried with it closed and opened, and halfway, and so on.

4. something else? there's a lot of left over cables from the carter systemů

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Unread 05-18-2012, 07:49 PM   #2
superj
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get a vacuum gauge from your local autoparts store.

to start it, find tdc and make sure your distributor rotor is pointing at the spark plug wire for number 1. that should be close enough to start. blindly turning the distributor might have messed you up enough to not start anymore. having to floor it to start makes me think your time is that far off. once you get it to start, we will give you instructions on using the vacuum gauge to set your carb properly
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Unread 05-18-2012, 08:15 PM   #3
Jax89Jeeper
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You should also check that your idle screws on the carb are set to the correct initial setting. Turn them all the way IN carefully making sure they bottom out, but don't tighten them down any further. Then turn them back OUT to 2 1/2 turns each, this is the correct starting point and it can be tuned from there using a vac gage. You should also make sure the idle screw on the throttle arm is not backed too far out... The fact you can get it to run at WOT could be timing, but if it ran before the carb install it is more likely the base carb settings are off.
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Unread 05-18-2012, 08:17 PM   #4
orengutan
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these might be obvious questions, so I'm apologizing in advance, but I'm learning as I go

how do I find tdc without taking the engine apart? do I just plug the vac gauge into spark plug 1, measure the pull and find the 'peak' of vacuum?

and how would this make it start+idle properly? or is this setting 'base' timing for me?
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Unread 05-18-2012, 09:13 PM   #5
superj
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to find tdc easily, pull the number 1 spark plug and put your thumb over the hole while you have someone turn the crank over with a ratchet. when the engine is on tdc, the air in the cylinder will push your thumb off the hole.

base timing would be about 8 degrees but getting it roughed in, one of hte ways i listed above will get you close enough that it should start, if the carb is not all funky. set the carb like jax89 said to but make sure to NOT turn the two little idle screws on the bottom of the carb that point outwards in too tight or they will enlarge the little mixture hole and ruin the carb. turn them in until they lightly bottom, or stop turning easily. the curb idle speed screw is on the throttle arm where your throttle cable attached. its on the bottom of the arm and pushes the arm away from the stop when you turn the screw clockwise, which opens your throttle plate and raises your idle.
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Unread 05-21-2012, 05:54 PM   #6
orengutan
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Ok. So. Very interesting stuff that I've always wanted to understand. Thanks for the tips guys!

Assuming that spark plug 1 is aiming toward the front of the car, I've set TDC and pointed the dist at spark 1. Minimal, if any, improvement.

I also made sure that the idle screws are set to 2.5 turns, and played around with the screw on the throttle that sets idle.

None of these things have resolved my problem. Still no idle... I don't want to blame the carb because I did have ****ty idle before I nuttered it, so somewhere between nuttering, advancing the dist (I used a light at that point), and applying rtv, I screwed things up.
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Unread 05-21-2012, 07:56 PM   #7
superj
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where did you rtv? and, did you restart after doing the nutter or did you do all your mods at once? did you happen to remove the spark plug wires? the way you say unevenness of the running makes me wonder if a plug wire got switched with another accidentally? but if you didn't pull hte wires, that will not be a problem.

all you did was pull your old carb, put the adapter and new carb on and nutter? ok, first things first, unhook all vacuum lines from the carb and plug lines and cap ports on carb. make sure the port under the carb, the big one that goes to the valve cover is capped. all lines that were disturbed during your previous mods need to be capped or plugged.

start jeep. does it run better? if so, we know the carb is on right and one of the vacuum lines is not right or leaking
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Unread 05-21-2012, 08:17 PM   #8
orengutan
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I RTV'd on the manifold, and again on top of the adapter to the carb. basically, where I used to have normal gaskets, I used manifold liquid gasket marker (we dont have the same brands in canada that you guys do, so not actual "rtv". it's high temp, fuel safe, etc etc). it's pretty solid, so I dont expect any vac leaks.

there is only one port, and that's port vacuum on this carb. I actually have it plugged at the moment to help me diagnose what is happening. the other port, from manifold, goes to the brake booster/PCV.

so, I installed the new carb, started the jeep without vac advance hooked up, and it ran pretty unevenly, but mostly stayed running. I then nuttered, and ended up here. the wiring from the ignition module to the dist is basically it, given that I dont have the carter to modify. could I have missed a step there somewhere?
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Unread 05-23-2012, 11:49 AM   #9
orengutan
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is it possible that somewhere along the lines in my testing I messed up the distributor or the ignition module, causing these symptoms?
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Unread 05-23-2012, 12:41 PM   #10
orengutan
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actually that probably doesn't make sense. increased gassing wouldn't affect the ICM+dist voltage, I guess?
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Unread 05-24-2012, 10:19 AM   #11
orengutan
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what is this? a hot air choke hole? gonna block that off and see what happens…
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Unread 05-24-2012, 11:39 AM   #12
MTPKTS
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WOW!!! Thanks.

I am getting ready to do the same thing to my YJ, Got a new MC 2100 from a guy in Colorado. It came with all the stuff for the swap including the info for the nutter. I just hope I don`t have the problems you are having. Good luck figuring it out. Please post your findings incase I have some of the same issues.
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Unread 05-24-2012, 12:05 PM   #13
orengutan
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I am really at a loss here. out of guesses. I guess I'm going to start replacing things until I find something… starting with a battery.
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Unread 05-24-2012, 12:11 PM   #14
superj
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so what the heck is that empty hole you posted a picture of? any vacuum there?
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Unread 05-24-2012, 12:22 PM   #15
orengutan
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I dont know. I taped it off. zero difference. taped off anything else that looks like a hole around the choke.
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