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Discussion Starter · #1 ·
I am having a strong sputtering / stuttering while accelerating, so much so that the Jeep is almost undriveable. I have started to suspect the carburetor. I have timed it, retimed it, checked vacuum advance, checked spark plug gap, etc. This is a "rebuilt" carb, and when I got it I was unaware of two important things: it was rebuilt in 2007 (wow) and it has 1.23 size venturi holes. I just checked the side stamp on the carb. I had been wondering why it was sputtering / running so bad, and I think this could be the issue.

I bought a rebuild kit and was debating earlier whether or not to rebuild it, until I saw that. I am going to go to a junkyard and try to find a MC 2100 with size 1.08 venturis. I guess my main question is, could this finally be my problem?? I have been adjusting the idle mixture screws, timing, trying to track down other causes all day yesterday. It seems to idle fine, if I work the throttle by hand it sounded fine (up until today and it got more "gaspy") but when I try to drive it, it sputters like hell. Thanks, and I'm sorry that you guys are having to deal with me so much. I am new to carburetors, mechanical timing, etc, and have been reading / learning so much these past few weeks. Thanks for being so helpful, patient, and knowledgeable!
 

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You mentioned you checked the plug gaps, but did you check to make sure a wire didn't get crossed by accident? Mine was doing the same thing and I figured out my wife had crossed 2 plug wires helping me one day...
 

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Discussion Starter · #3 ·
Yeah, we chased them down yesterday and all is well (unfortunately) - I was wishing for an easy fix.
 

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I would almost guess its a vacuum leak at the carb to intake gasket. Check it by letting it idle then spray starting fluid around the carb and intake mating surfaces if the idle rises you've got vac leak. Im having the same problem right now and thats what I have found. The trouble im having is finding the adapter to intake gasket. Good luck with yours
 

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Put the origional Carter BBD back on it :rofl:
 

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Discussion Starter · #7 ·
I sprayed around the base with starting fluid - no leaks. And I've got most everything else capped off (useless emissions stuff). I am pretty sure it's not a leak, but I guess it still could be! Gonna try to find a Motorcraft with 1.08 stamped on the side. Could the 1.23 that I have now be feeding it too much gas, and constantly keeping it too rich?
 

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I sprayed around the base with starting fluid - no leaks. And I've got most everything else capped off (useless emissions stuff). I am pretty sure it's not a leak, but I guess it still could be! Gonna try to find a Motorcraft with 1.08 stamped on the side. Could the 1.23 that I have now be feeding it too much gas, and constantly keeping it too rich?
Did you try spraying where the intake meets the head it could be sucking air there also. What size jets you running? You will have to remove the top of the carb to see down in the float bowl.
 

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I didn't see in your posts that you checked the fuel filter or fuel pump?
 

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Discussion Starter · #10 ·
I didn't see in your posts that you checked the fuel filter or fuel pump?
Both are brand new. I bit the bullet and ordered the right carb today (1.08). I'm 74% convinced that the CFM differences were causing the mixture to be WAY too rich. I sprayed around the front of the intake manifold-to-block gasket, because I do have a SLIGHT oil leak there, but it didn't change RPM's.

Off topic, but I found a guy selling 5 carburetors for $30 total. 3 Rochesters, 1 Holley, and 1 Motorcraft (but 1.23 venturi size). I'm assuming they're all in need of rebuilds, but I'm wondering how much I'd be able to get from them on eBay or other places - I'm thinking at least $20/ea?
 

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I don't know enough to be definitive but I recently had an issue with my 2100 1.08. The venturi cluster was damaged (I damaged it cleaning it with Lemon Juice). I asked similar questions about venturi size since 1.08 seems harder to find these days and I was wondering about swapping venturi cluster. Like you, I was advised you could not to change sizes of just the cluster. I also searched ebay and found 1.14 and 1.21 to be cheaper preseumably since there more avaiable than the 1,08. However, in my search I found also found this:

#108 is 450 cfm, #114 520 cfm, and #121 575.

I read that the 1.21 is basically for the 360; possibly 4 barrel. So if you are running it on 304 2bbl, I suppose you could be right about running too rich. Although I have read posts where some people are running 1.14 w a 304. Not sure if I found anyone using a 1.21 but you should search the threads. I'm sure there is someone that has at least tried it. I ending up posting an add on this forum for an old 2100 I could use for parts. I picked up 2, popped in the venturi cluster (1.08) and it started right up and seems to run pretty good (after a cleaning and rebuild of course).

Please see my thread on a beginners experience with cleaning a carb

http://www.jeepforum.com/forum/f8/craigslist-cj8-build-1555241/

Please let us know your results with your new carb....
 

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i agree with the 1.08 being the much preferred size for most applications. i rebuilt the 2100 when re-doing the engine (read: no more smog junk) on my 1983 ford ranger, 2.8 v6. along with the duraspark swap, it has been running great for the past 5+ years. good luck for sure.
 

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Discussion Starter · #14 ·
I swapped the carburetor today with the 1.08. Not much, if any, of a difference. I'm pretty sad/disappointed about now! The spark plugs are NOT black/fouled - they have a nice ash-tan look to them, and I double checked the gaps. I have a limited lifetime warranty on the cap/rotor, so I am replacing those tomorrow. If you look in the cap you can see how the rotor button has BARELY contacted the points, scraping away at them ever-so-slightly. I am also getting a new set of plug wires, to rule that out. I checked the rubber hoses coming from the gas tank to the steel lines, and they weren't bent - I had a problem a few months ago where I wasn't getting any fuel, and it turned out I had a kink in the rubber hose coming out of the gas tank, so I replaced both of those with fresh hoses. I will fine-tune the idle mixture screws tomorrow, but I think it won't make a huge difference. Vacuum advance line from the distributor is hooked up to the side of the carb, and I set the timing to 12 advanced. It will idle pretty well, and even when I sit there at an idle and manually work the throttle cable, it will accelerate / act responsive. Then, when I drive it under load, it wants to lurch forward / back and hesitate like hell. It almost stalled out on me today!! I pulled the distributor to check the teeth on the gear for wear / damage, and nothing. Guess that's a good sign! Could it be my ignition coil? I was told if it wasn't getting a hot enough spark under load, that it could cause symptoms like this. I just don't know! Thought the carb was going to solve it.
 

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Such as is common to man

Great thread, thank you for sharing your journey. I am struggling with the same thing. I upgraded to the Motorcraft 2100 last winter on my 1982 CJ7 straight 6cyl snowplow war wagon. I bought the carb from a jeep carb expert with lots of experience (Gronk). I was happy all around with Gronk. As I recall she ran much better after the Motorcraft was installed. However after sitting all summer, she does not want to run right. sputters, dies under load, need to tickle the accelerator pump to keep it running, (thus the pronoun 'she'). Drained fuel tank back to front, new filters, new fuel pump, flow is good; fuel supply is not the problem. I tightened the carb mounting bolts and resealed all the unused vac ports. Used propane to sniff out vac leaks, found none. I will repeat this leak test with starting fluid and check all the way back to the block/intake manifold joint. My gut tells me its a vacuum leak. Primary symptom is when I holding a steady high idle with the accelerator pedal, I expect it to hold steady at that RPM indefinitely and smoothly. However what happens is the engine performs correctly for about 2 or 3 seconds and then starts coughing, sputtering dying out. It sounds like it is not getting enough fuel into the cylinders. Again fuel supply to the carb is good. So if there is a vac leak then there is not enough vac to pull the fuel through the carb ??? Not sure how a carb works in detail. Any thoughts gentlemen?
 

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Reviving an old thread.....again.
Two weeks ago switched carb on Gramps out from Solex to MC 2100 on '81 CJ5, 258 I6, 4 spd. This carb came from Mongo228's Klooge, which it was running good on his Jeep with same engine, but I have some added emissions equipment he did not have. Hence, having issues getting the carb to smooth out and run properly, and thought JF members might have some good input to advise, as it is driveable but with some issues.
Note - the carb itself has settled down and idles/raps up good in driveway, with a little tweaking, but seems the emissions equipment might be to blame for the poor driving performance. Auto choke does not seem to work correctly at any setting, and when driving cold, wants to cough and fall between shifting up and trying to accelerate. Runs better the more it gets up to normal temp. Sounds like cough is from back fire preventer, and guessing fall is possible vacuum feed/timing adjustment needed.

I will get pics, and project summary tonight, to better detail the issues.

Thanks all
 

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The very reason I had to get rid of my '85 Nissan 4x4 was vacuum leaks... not from gasket mounting surfaces, though. The hoses themselves had grown brittle over the years and when cold would shrink (which would open up cracks creating the leaks)... when they warmed up, they fattened up, plugged the cracks (and leaks) and it ran great.

I would start up the truck in the morning, and it idled great! Once I put it in gear and tried to drive, it bucked like a bronco until it had truly 'warmed up.' The afternoons were no big deal - ran fine. Nothing I tried seemed to work. I first swapped plugs, then cap & rotor, then wires, then coils (Z-24 engine, dual-firing = 2 plugs per cylinder & 2 coils w/a giant 8-hole dizzy cap), then even went so far to swap carbs - bought one from a salvage yard and rebuild it - no change. None of those things seemed to work because after changing them, I'd run the engine for a little bit, which was then warm - no issues. But then first thing in the morning during fall when the temps were dropping a bit at night, that problem crept back in.

I even caved in, went to the Nissan stealership and let their technicians take a crack at it - to no avail. They actually made things worse - it wouldn't even start, and then the [*******] mechanic jumped the idle up to 2000rpm and called it good. After paying almost $200 for them to tinker with it, I demanded the service manager make it right, since they'd made it worse, and he reluctantly agreed for me to drop it off the next morning... to which he called me a few hours later and said my ECU was bad. Finally! OK - how much would that cost? $1600+. WTAF?! He argued with me that even though the ECU was 'only' $400, there was more to it that simply taking out the driver seat, swapping the ECU, putting the seat back in, and making adjustments to the carb afterward. Ummm - B.S., and EFF that! They'd done enough, so I struggled with it a few more weeks, then finally traded it in on a '78 K5 Blazer Mongo and I had been drooling over for a few weeks, and later bumped into the kid that eventually bought my Nissan, and he'd swapped the vacuum lines to fix it. He'd also smashed in the driver door, broke the windshield and a couple of headlights, and crunched the bumper - while 'boonie bouncin' as he put it. Lesson #1 hard learned of 'never sell a car you care about to anyone in the local area... especially, not to someone you know.'

I pulled my hair out for a few months over that - ask Mongo - and was pissed to find out the whole issue was resolved with less than $10 of new vacuum lines. I loved that truck - it was bad-***. I still miss it, actually. (I actually miss all my cars I don't have anymore - they were all cool in their own ways).

Vacuum hoses. Don't ignore 'em.
 

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That is the next step, as the carb (as I see it), is running as best it can. Had a vacuum issue last spring, and upon changing a couple hose connections, created a similar problem. So going to work off FSM vacuum diagram and connect like it should be. One of the PO's had the fuel return line, hooked up to emissions switch on valve cover drawing vapor off the tank direct, and into the air pump system pushing to the exhaust manifold. When we put the 2100 on, with dual port filter, traced the return line and found how it was connected. Rerouted it for return line, now need to replace vapor feed through charcoal canister. In doing that, will also need to correctly hook up other vac lines correctly, and I think it will run like it should.

Driveable, and a HUGE improvement over the old Solex carb (keeping it in a box marked "Historical Item" for training purposes), and will get the vac issues sorted.

Thanks for feedback :)
 

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Ok MC2100/114 guru's...
Seems my 55 yr old 2100 is suffering from wear around the main throttle shaft, primarily on the outboard side where the throttle cable attaches.
In the driveway when starting cold, it runs like crap, and need to keep bobbing the pedal to keep it running. The more the engine warms up, it will eventually idle, but still up/down a little on rpm's. Checked for leaks around base plate, single vac port on the carb, and all other vac lines on the engine to make sure nothing is overlooked. Carb had rebuild about a year ago, ran just a little, then drained/bagged and shelved. When I got it for Gramps, we (Mongo228 and I) went through it to make sure all was good, then installed it and had some vac leak issues. The major ones have been resolved, but finding one still around the base of the casting, on main throttle shaft.

Looking for input as I want to repair this carb, and asking if there are different size shafts available for replacement, or do I drill/sleeve the casting with existing shaft? My assumption is the aluminum casting is softer metal than the shaft, so asking for "best" advice before moving forward, from any/all the MC2100 vets out there.

Also thinking of taking the auto choke off, and going with a manual choke cable. Grew up with the manual type, so very familiar with them.

Thanks for feedback.
 

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