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Unread 12-07-2013, 06:24 PM   #1
Wrenchtosser
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1990 YJ Wrangler 
 
Join Date: Jul 2012
Location: Roseburg, Oregon
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Rough running/stalling after Nutter and Motorcraft 2100 install

Hey guys, need some help troubleshooting this one on my 1990 YJ 4.2l....

Just finished installing a newly rebuilt Motorcraft 2100 carb (from the eBay guy everyone seems to recommend) then completed the Nutter bypass mod.

Symptoms:
- bad miss throughout RPM range
- rough idle
- seems to buck and surge, especially around 1200 rpm
- stalls after driving for short period of time at relatively steady state RPM

Here's some background info:

- Carb installed correctly, checked for vacuum leaks.
- Linkage adjusted
- timing 8 degrees btdc, dist vacuum now ported, as per Nutter instructions
- the two idle mixture screws set (in tandem) to obtain max vacuum at idle
- fuel pressure checked and correct, new fuel filter and pump
- EGR vacuum connected correctly
- tune up parts are about a year old but in good shape, plugs are 6 mo old

At this point, Im kind of getting to the end of my list of things to check. I was having this same issue before the Nutter and carb swap, but it does seem worse now. I had hoped (obviously) the carb swap and Nutter would fix these crappy running issues.

As mentioned before, this is a 1990 YJ with a 4.2l and manual trans

Ideas? Suggestions?
Im running out of ideas.

Thank you in advance.

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Unread 12-07-2013, 06:30 PM   #2
superj
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I would bump the Timing up a little. 10 or 12. Also, run some extra grounds in the engine area. Not sure if you have a ground problem but they normally help

If you cap the vacuum at the carb and try it out, does it do the same thing? We just got my buddies jeep going and it was having a heck of a time. Capped the vacuum port at the carb to recheck everything and suddenly the jeep ran perfectly. Something is up with his vacuum advance but now its toooooooo cold to work on the jeeps
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Unread 12-07-2013, 06:44 PM   #3
Wrenchtosser
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Quote:
Originally Posted by superj View Post
I would bump the Timing up a little. 10 or 12. Also, run some extra grounds in the engine area. Not sure if you have a ground problem but they normally help

If you cap the vacuum at the carb and try it out, does it do the same thing? We just got my buddies jeep going and it was having a heck of a time. Capped the vacuum port at the carb to recheck everything and suddenly the jeep ran perfectly. Something is up with his vacuum advance but now its toooooooo cold to work on the jeeps
And I know what you mean about too cold to mess around with this as its been in been in the 20s this week, and supposed to be about 8 degrees tonight, but I have to get this running so I can drive it, or its a long, long walk to town!

I've messed with the timing and idle speed both, and had no improvements. The rough running and poor idle seems just as crappy no matter what I did there. Ill give the vacuum cap a try for sure, thanks for the idea.
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Unread 12-07-2013, 07:17 PM   #4
Old4X
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The nutter instructions are incorrect on vacuum source for the advance. The engine will run better, make better power and get better gas mileage with manifold vacuum.

You will have to retune your carb and adjust the advance limiter in the dizzy to make it run right. When close you can fine tune it with the advance can adjustment screw.

Which "window" on your advance plate are you using now?

And what are you using for an air filter (flow rate?)

Are you using a stock type fuel pump and filter?

Is your vent system to the charcoal cannister hooked up and operating properly?
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Unread 12-07-2013, 07:18 PM   #5
Old4X
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Also, what is your vac reading at idle?

Have you run a compression test?
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Unread 12-07-2013, 07:37 PM   #6
Wrenchtosser
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Quote:
Originally Posted by Old4X View Post
The nutter instructions are incorrect on vacuum source for the advance. The engine will run better, make better power and get better gas mileage with manifold vacuum.

Which "window" on your advance plate are you using now?

And what are you using for an air filter (flow rate?)

Are you using a stock type fuel pump and filter?

Is your vent system to the charcoal cannister hooked up and operating properly?
Wow, this is the first Ive ever heard that manifold was better than ported with a Nuttered 258. Honestly, I ran manifold vacuum at first and had a severe off-idle hesitation. After changing my distributor vacuum feed to ported that problem went away.

Answers to the questions:

Distributor advance plate window: I haven't made any changes there at all, so it is still on the factory setting

Air Filter: Currently, no air filter is on this carb as the adapter I ordered was missing parts. As my primary problem is a bad miss, I wouldn't suspect air flow problems, but I've been wrong many times before.

Fuel pump and fuel filter: both stock replacement parts

manifold vacuum reading: I wish I would have recorded it...I wasn't really looking at numbers when I was tuning the carb, just trying to achieve the highest possible readings. I can tell you the needle was 25% of the way around the dial, however I have no idea how many inches of vacuum that was, and as it is 20 degrees right now with a foot of snow on the ground and the garage where my tools are and jeep is parked 25 yards from the house, Ill have to wait to go look at the gauge again to check it!

Last edited by Wrenchtosser; 12-07-2013 at 09:39 PM..
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Unread 12-07-2013, 08:03 PM   #7
Old4X
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If you nuttered it and left the dizzy stock, you are leaving most of your performance and gas mileage on the floor. Ignition advance was largely controlled by the computer. Your centrifugal advance is limited by a limiter plate. If yours is still stock the limiter window (there are 2 on each plate something like 5 and 7 , or 14 and 18, IIRC) is probably the 5 degree window. The computer added more as needed according to what the sensors told it. Your has has the smog plate (5,7) pre smog dizzys had the other (14,18)

With a stock distributor and a nuttered ignition, it is like trying to run it with a sock stuffed down the carb throat. You are running your ignition as much as 13 degrees retarded from what the engine needs for the load.

There are plenty of writeups on this, sorry I do not have the links right now, but it is common knowledge on these Motorcraft Duraspark systems.

On vac reading, you should have around 21" at idle minus an inch/thousand feet above sealevel, more or less depending on conditions. Needle should be steady
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Unread 12-07-2013, 08:12 PM   #8
Old4X
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There is a bit of a disagreement on vac source for advance. Ported is more for emission controls and is why it was first introduced. Automobile engines had run manifold advance exclusively until the emission stuff started.

Ported will make the engine run hotter at idle, as it retards the ignition.

Once you get everything dialed in, try it both ways and check gas mileage and drivability on several tanks on each. Your driving style may suit the ported , but for me, the manifold is way better as far as power and fuel mileage.
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Unread 12-07-2013, 08:19 PM   #9
superj
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Here you go.

http://www.jeepz.com/forum/cj-yj-tj-...stributor.html
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Unread 12-07-2013, 08:33 PM   #10
Wrenchtosser
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Quote:
Originally Posted by Old4X View Post
If you nuttered it and left the dizzy stock, you are leaving most of your performance and gas mileage on the floor...with a stock distributor and a nuttered ignition, it is like trying to run it with a sock stuffed down the carb throat...On vac reading, you should have around 21" at idle minus an inch/thousand feet above sealevel, more or less depending on conditions. Needle should be steady
Wow, I really appreciate this info. I had actually done a great deal of reading up on this before doing these mods, and I have to say that this is first I've heard about additional distributor mods being necessary to make the Nutter mod work correctly. But as you've obviously been able to obtain some impressive results (22 mpg!), I'm listening to the voice of experience.

As far as that miss goes, I'm actually starting to wonder if I have a bent push rod or something. Im not really hearing a lot of funky mechanical noises from my engine, however is sure is acting like this may be the culprit. You asked about a compression test - I don't have tools for that, unfortunately.
However, as I need to replace the VC gasket anyway, Im going to pull the valve cover as soon as can get a new gasket and check for bent push rods, and broken rockers and valve springs.
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Unread 12-07-2013, 08:47 PM   #11
Old4X
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You can borrow a tester from an auto parts store, they require a deposit for full value, but refund on return.

Your vac gauge can tell you if you have valve issues. A steady needle at idle says a lot about the health of the engine. Instructions that come with the gauges tell you what other than steady readings mean.

Also, do you know how much slack you have in your timing chain? When I got mine, I had over 16 degrees of slack. Replacement is recommended for anything over 6 degrees.
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Unread 12-07-2013, 08:48 PM   #12
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You said you checked well for vacuum leaks. Did you check torque on the intake manifold bolts in the head? They tend to work loose.
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Unread 12-07-2013, 08:54 PM   #13
Wrenchtosser
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Quote:
Originally Posted by Old4X View Post
You can borrow a tester from an auto parts store, they require a deposit for full value, but refund on return.

Your vac gauge can tell you if you have valve issues. A steady needle at idle says a lot about the health of the engine. Instructions that come with the gauges tell you what other than steady readings mean.

Also, do you know how much slack you have in your timing chain? When I got mine, I had over 16 degrees of slack. Replacement is recommended for anything over 6 degrees.
Compression tester: Yep, borrowing one is a good idea. Problem is I live out in the mountains, in the middle of nowhere and it is about an hour drive to anything that resembles a town...but when I go there to get a new VC gasket, Ill borrow that tool, too. Trying to do as much as I can with what I have here, first.

Vacuum gauge readings: I forgot to answer one of your earlier questions, but I remember my vac gauge needle being dead steady, not wavering, which (to my understanding) would indicate good valves/pushrods/springs, etc...right? I got the gauge at a garage sale with now instructions, however Im sure I can find more info on using it on the good ol' internet!

Timing chain: My engine has 190k miles on it, so I have no doubt it needs a new one. But - before I started having Carter BBS carb issues, I was amazed how strong of a runner that engine was. For the mileage, it seems to be very solid. Hope Im right.

Thanks again for your time and sharing of info.
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Unread 12-07-2013, 08:56 PM   #14
Old4X
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"Vacuum gauge readings: I forgot to answer one of your earlier questions, but I remember my vac gauge needle being dead steady, not wavering, which (to my understanding) would indicate good valves/pushrods/springs, etc...right?"

That is my understanding
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Unread 12-07-2013, 09:10 PM   #15
Wrenchtosser
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Also, forgot to mention - I was pulling about 14 - 15 inches of vacuum, but since you said I should have been seeing about 21, that makes me wonder. I seem to remember the needle being steady during the reading, only moving when I adjusted the idle mixture screws.

I live at about 1400 ft, but that wouldn't get me to 14 inches. As that was a garage sale gauge, I wasn't trusting the reading's accuracy...mostly just looking for consistency and the highest vacuum inches I could pull. That gauge may be way off, for all I know, or I have vacuum problem somewhere.

Last edited by Wrenchtosser; 12-07-2013 at 09:39 PM..
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