Yet another MC2100 situation - Page 4 - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #31 of (permalink) Old 07-10-2009, 12:08 PM Thread Starter
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There are 8 possible configurations and I have tried each of them, test drove in each, no change. The linkage itself could possibly use some tweaking though. Guess I didnt think about that, even though I read it in someone elses thread. Oops. I will also check the float level again this weekend. Maybe the accel pump isn't always being fed a good amount of fuel to properly function. I will also check psi from the fuel pump to make sure it can keep up with carb delivery. Thank you for the reply, it got me thinking again.

'88 YJ
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post #32 of (permalink) Old 07-10-2009, 07:44 PM
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"""""I did not turn them in to see if it died. I started at 2 turns out each and adjusted evenly from there. """""

Why don't you want to follow instructions? Setting the mixture screws properly also sets the transfer circuit - the transition between Idle and main run.
It's not rocket science.

What happened when you followed the instructions using propane called out in "propane trick?

We cannot help if you don't do what we say.
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post #33 of (permalink) Old 07-13-2009, 09:28 AM Thread Starter
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Let me re-phrase, I have not had the time to simply turn in the mixture screws all the way to see if the jeep will die. I have not had the time to connect a tube to the carburetor throat via the air cleaner and run it back to a bottle of propane in the cab. I have done this in the past and it has helped greatly with the diagnosis of carburetor problems.
I hope that this won't cause any negative feelings but in my defense, another reason why I went away from troubleshooting the carb was a response that you made in one of your replies at the beginning of this thread:
Two carbs, both with the exact same symptoms? What are the chances 10 more will be any different?

My feeling - ignition.

So I went with that, your suggestion. So really, have I not done what you have said? I have been working with the ignition lately. My plan now is to copy and paste to Word this thread and go through the suggestions step by step to diagnose the problem, not moving to the next until one is ruled out.

I also have planned to organize, in a logical sequence, some sort of a "try this" or "have you done this" write up so that people can go to it for general ignition and carburetor troubleshooting before coming to the point where a new thread about the MC2100 is required. A sort of catch all for those that don't like to search. Is there one already in place? Most likely. And yes, I would like to have someone else proof read for errors before it gets posted. Have I been guilty of asking before searching? Definately. Was I this time? Most of you will say yes and as of now, I believe you to be correct. When I started this thread, I didn't feel as though I got the correct answer from the search results. But in turn, it all has led back to very similar issues others have complained about. I am willing to save the experts some time by collecting info from this thread and others and posting it either as a sticky or as a tech article, if it is authorized. And, most importantly, I will give credit where credit is due.

I will let you know the outcome of the troubleshooting. Thank you again for your valuable time.

'88 YJ
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post #34 of (permalink) Old 07-13-2009, 02:46 PM
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"""""I have not had the time to simply turn in the mixture screws all the way"""""

Funny, the time it takes to turn the screw in 1, 2, or 3 turns to find the point where it stumbles, then back it out 1/2 turn is less than it took to write why you didn't have time to do it. It's a few simple twists of the wrist.

That sets the carb to very close to where it should be. It gets the idle mixture close as well as the transfer circuits. If it's still not right after that, I suggested looking into the ignition.

But - you seem to know all that, so why did you take the time to ask initially?
Writing and posting it it took more time than should have taken to track down the problem. It's not rocket science, just following a logical sequence.

Have a good day
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post #35 of (permalink) Old 07-14-2009, 09:29 AM Thread Starter
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I never said that I didnt set the idle mixture screws, they are set. I said that I did not screw them in all the way to simply check if the engine would die, an even easier task to accomplish. Therefore, I went with your's and TR's guidance (along with the other folks') and checked into the ignition system as suggested.
Why did I post initially? I answered that in the previous post I believe. I was looking for something that I missed. It isn't rocket science, like you said. Following a logical sequence is where I think a lot of people's questions stem from. "Jeep aint runnin right so I pulled the engine only to find a leak in the carb base plate. I did this this and this, what next? Put the engine back in and turn the key"...Sometimes people, no matter how knowledgable they may be, need a little guidance to overcome their frustration.
I've learned a lot about a lot just by reading posts from others, or starting a thread of my own.
I have a great deal of respect for those like yourself and TR. It takes a good person all together to use their personal time and knowledge to provide this information to the community...and all we have to do is pay for the ability to log onto the internet. I'm sure people post questions on here EXPECTING to get an answer, and they almost always do. Believe me, I have been using the information given to me.
Thank you again for your time.

'88 YJ
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post #36 of (permalink) Old 07-14-2009, 12:50 PM
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It's very unusual for an engine to die because one screw is turned all the way in. But if the carb is really misadjusted or defective it can happen.
Usually when the screw is turned all the way in it just runs slower - and still should run smooth. That's a valid test. The "stumble point" is only about 1/2 to 1 turn out from fully closed (time? - 1 second?)

WHY? Each side of the carb feeds 4 cylinders on your V8. Look at the runners on the intake manifold.
The carb's left side feeds the 2 end cylinders on the left side, and it feeds the center 2 cylinders on the right side, for a total of 4. The other side of the carb feeds the other 4 the same way. Yes, there is some mixing of gasses in the plenum where it's open (sometimes,) but essentially they are 2 independent systems.

If you look at the firing order, you'll find those are every other cylinder in the firing order.
And they are also a balanced set.

If all 4 of those cylinders were to quit firing, the other 4 will still fire, and since they are every other one, and mechanically they are balanced, the engine will run fine, smooth, just not as much power.

If one side of the carb isn't working, and you shut off the other, yes it will die. And when you shut off one side and it doesn't run smooth, it shows that one of the remaining 4 has a problem.

We did not go into a deep explanation as to the how and why, we just needed to know the reaction. It's only 1/2 to 1 turn anyway, but it tells alot.
On here there isn't room or time to get deep into theory if we are to help. Just believe us - unless you think we are crazy.

I think we both have been on here long enough for you to realize I don't believe in throwing parts at something - guessing - I'm a believer in testing, then verifying, then if needed, replace. Yes, there are some that are the opposite, "replace everything in sight till it works."

I never ask anyone to use sophisticated test equipment unless it's absolutely needed, even though I own most of those things.

KISS is my byline.
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