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Unread 10-18-2011, 02:27 PM   #1
paintguy
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MC2100 Problem>>>Help Please!!!

Hello All -- I haven't posted in a while but I used to be very active on the boards helping out when I used to work on YJ's so sorry for now coming and posting a new thread b/c I have a problem. Thank you in advance for any and all help I know I will receive here!!

I have an "89 YJ Laredo with the 4.2 automatic -- I did the "nutter bypass" about three years ago with the MC2100 and it has been running awesome until last week -- I hit a decent mound of gravel in the road from the heavy rains and she sputtered a little and then picked back up again and ran fine until a 1/4 mile later I pulled into the local gas-n-sip and she just stalled?? She has never done this before...I started her back up and she started hard and idled funny and stalled -- also, the smell of sulfur ("rotten eggs") spewing in the air when I got out?? I did replace the cat a few days ago with no change (it was under warranty from Advance so no monetary loss).

The biggest thing I can tell you is I can turn my air/fuel mixture screws all the way in until they seat and she doesn't stall or anything?? they are usually set 3.5 turns out each. Also, the plugs are black. Seems like something failed that is making it run rich (hence the rotten egg smell out of the exhaust) and the black plugs. Why can I turn the air/fuel screws all the way in?? I am thinking something in the carb failed that is causing it to run rich. It "lopes" at idle sometimes and sometimes it idles fine?? Usually it will stall when coming to a stop in gear unless at give it a little throttle?? Starting is hard also hot or cold?? I did replace the fuel filter and checked the hei unit internally to rule those out. I also put 10g of fresh gas in and a little lucas fuel treatment to rule water in the fuel out.
I look forward to any and all responses to my thread -- THANK YOU!! AND PEACE TO ALL!!

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Unread 10-18-2011, 05:34 PM   #2
raynmaker
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could be a few things. any of the diaphrams or gaskets on the carb could be bad. Your ignition modual might have failed. or your fuel pump might be having issues.
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Unread 10-18-2011, 05:51 PM   #3
Thumper01
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you also might want to pull your distributor cap and check to see if it is carbon tracking: firing where it is not supposed to. make sure your distributor is tight and has not come loose changing the timing.
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Unread 10-18-2011, 05:55 PM   #4
mudsweatNgearz
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Sounds like a timing issue.
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Unread 10-18-2011, 05:59 PM   #5
4.7stroker
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I would pop the top off of the carb and make sure that the float needle is seated. You can run the engine with the top off of the carb to see what is going on in there.
Sounds like the bump dislodged the float/needle from it's seat causing flooding. You could have also sucked some crud up into the filter causing a lean condition(not likely because of the black plugs).
Not likely ICM or fuel pump because it will start it just runs like garbage.

Dwayne
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Unread 10-18-2011, 07:23 PM   #6
lah2420
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I second what 4.7stroker said. Sounds like the needle/seat has a problem or the float got dislodged somehow. I had needle/seat issues at one time and it would visibly shoot gas into the throat of the carb at idle.
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Unread 10-19-2011, 05:23 AM   #7
paintguy
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ok -- i did take the air cleaner off the carb and do not see any fuel at idle dripping or spraying into the carb from the venturi tubes at idle -- is this what your are referring to stoker4.7? also, i have to turn up the idle to about 1000 so it does not lope and then stall to do this -- would that "mask" any dripping or spraying b/c it is not at normal idle rpm? I will try to do it at 750 rpm and report back. Also, where is the float needle located and how can i check if it is seated or not? I probably have to take the carb off to check or possibly dislodge the float if it is stuck right?
One more thing, I changed the fuel filter just to rule it out and the old one rattled inside like a big pvc valve when I shook it and the new one is solid inside like it should be -- is this a clue to anything??
Thank you all for the replies so far -- i (we) will get this thing figured out before I move to a weber (which I hope I do not have to do!)!!
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Unread 10-19-2011, 06:24 AM   #8
4.7stroker
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To check the float level you hve to take the top off of the carb. It is usually held on by 5 screws.
You will simply remove the screw holding the choke flap rod and remove the tear drop piece of linkage from it.
Remove the screws that hold the top on the carb.
Use care and lift the top, try not to rip the gasket.
The float level should keep your fuel level 1/2" below the rim of the bowl.
BTW some pics will go a long way to making sure you get it back together right.

Dwayne
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Unread 10-19-2011, 07:18 AM   #9
paintguy
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OK 4.7stroker -- thank you. I actually am thinking it is something in my hei -- maybe a short in the coil? i bought it from CRT Performance when I did the nutter bypass about 3 years ago or a little more. I am almost done now cleaning the hei out/tightening/inspecting it. Also, I have just noticed that advancing or retarding the timing via the hei doesn't make too much of a change -- it should stall out if I retard too much or idle crazy high if advanced too much right?!! I hope it didn't skip a timing gear but will get the timing light from my buddy today to rule that out. Lastly, the engine doesn't want to turn off in park or neutral sometimes especially when the engine is at normal operating temperature??? It will shut off in about 5 seconds or when I give it throttle or shut it off in drive??
Any ideas about those new findings/issues? I will report back soon -- thanks again everyone for the replies especially you 4.7stroker!
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Unread 10-19-2011, 07:24 AM   #10
oldtime_ironman
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Pretty sure its the carb, regardless. Especially with running rich and running on. Even if the float valve seats, the float arm could have bent. So I would first be sure its seating properly, the check (measure) the float height.
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Unread 10-19-2011, 07:39 AM   #11
paintguy
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actually the engine does not want to shut off in park or drive unless I give it some throttle?? no change after cleaning hei contacts and internals and making sure anything is tight. I believe, from all your replies, that it is either the timing chain skipped a gear, the carb is letting in too much fuel or the coil is shot and grounding out. BTW, she runs pretty good at highway speed or under hard acceleration, but not as good as she did before the bump and this issue??? That really makes me think it is not a timing issue but a float/needle issue -- any thoughts on that? Thank You!!!
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Unread 10-19-2011, 07:50 AM   #12
mcmud
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Idle mixture screws having little/no effect added to the irregular idle (sometimes rich, sometimes lean)and what reads as dieseling are classic symptoms of having the throttle plate (idle speed screw) set to far open. Back off on that screw to the point that the mixture screws come into play.
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Unread 10-19-2011, 07:24 PM   #13
4.7stroker
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If you had a bad coil it would not run.
If you had skipped timing it would not run good at highway speeds.
Part of the art of trouble shooting is to be able to eliminate systems by looking at the symptoms then only looking at what makes sence.
I am going out on a limb and say it is your carb or fuel related.

Dwayne
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Unread 10-20-2011, 10:53 AM   #14
Alabamaranger
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I would check the power valve. We put a 2150 on a vehicle last night. The idle screws had no affect. It was running RICH so bad it was loping. Removed the carb and took the cover off the power valve (bottom of carb) and the power valve was loose - hand tight - plus it had fuel inside the cover when removed. Not suppose to be any gas in that cover, if you do -it's bad or loose in my case.

Anyway, I had a new power valve so we stuck on in and tighen the cover back up. Put it back on the engine and ran like a top.
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Unread 10-21-2011, 02:18 PM   #15
paintguy
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Well, here is what I have found: The carb has an air leak at where the throttle linkage arm exits the side -- this happened with the first mc2100 I installed when I originally did the nutter bypass -- luckily, the guy I bought the carb from sent me another and it solved the issue. The reason I know it is leaking where the throttle linkage comes out of the carb, is that when I spray carb cleaner directly in that spot with the red spray tube the motor will attempt to stall. This explains why my air/fuel screws can be turned all the way in and not greatly affect how it runs (which it normally would in the past). The question is, is why when I hit the bump in the road did this happen?? I can't answer that at this time, but I do not believe in coincidences....
Thank you all for your help -- I am just glad I know what is going on with it now and plan on trying a new redline weber carb because all the mc2100's are remaned.
Does anyone have a pic of their mc2100 throttle linkage where the spring(s) are on the driver;s side of the carb? My only thought is that I had two springs and one flew off when I hit the bump!! I can't remember if there was a second one on there b/c there are two linkage arms on that side???
Thank you!!
PEACE!!
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