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How to - Nutter Bypass

414K views 505 replies 176 participants last post by  KDub1984CJ7 
#1 · (Edited by Moderator)
Ok, for all those who want to perform the Nutter Bypass to eliminate the Electronic Control Module from your '83 and later CJs and YJ's with 4.2L engines & BBD carb, here's the how to.

I know I had a lot of questions before doing it about how to, etc., and I've seen a lot of others asking questions, so I figured why not create this so that, hopefully, most questions are answered. A little preparation on the front end saves a lot of headaches on the back end, right?

This is NOT a 'why should it be done post? For that, you should do other searches and then come back to this if you decide to do it.

It's easy to do, and it did benefit me. I no longer have the rough idle, including my Jeep's 'cough' during idle. My gas mileage prior to the bypass was 16.2mpg. After filling it up and emptying a tank, it was at 18.7mpg. That was with a lot of stop and go and even a little mudding.

Also, a BIG THANKS!! goes to Mike Romain, who read over, corrected, and helped a lot with this write up. :cheers2:

So without further ado, here it goes. Step by step (with pictures!!). :2thumbsup:

Stepper Motor Needle adjustment: Steps 1 & 2

Step 1: Adjust the stepper motor needles in the carb so that the shoulder sticks 1/8" into the carb.

Stock stepper pins run in the middle of their travel which is when their shoulder is 1/8" to 1/4" away from the carb wall (closer to 1/8" is preferable). Several people have set their pins at this level and have reported improved results over the 'full rich' setting in John Nutter's original setup. Some of these jeeps have also passed emissions testing with the needles set in this position. Of course, it's a Jeep thing, and your results may vary.

To get your stepper pins the way you want them, the easiest way would be to remove the stepper motor from the back of the carb and adjust the pins, then re-insert and affix the motor to the carb. Ensure you did not move the pins when re-inserting the motor.

Another option is to adjust your idle mixture screws on the front of the carb while the engine is running: Out (counter-clockwise) - to have the stepper pins move into the carb and create a full, rich condition, or In (clockwise) - to have the pins move into the stepper motor to create a more lean condition.

Step 2: If you choose to adjust the stepper pins using the idle mixture screws method, once the stepper pins are at the level you choose, turn the ignition off and unplug the electrical box from the back of the stepper motor (remains unplugged forevermore).



Re-routing wiring: Steps 3-11

Here is a link to a diagram of before and after wiring... Blog | Earthlink

Step 3: Find the orange and purple wires at the distributor.



Step 4: Follow the wires through the wire loom to where they enter the firewall (it may be necessary to remove the loom).

Note (Read prior to Step 5): It is sometimes recommended that you do not cut into the wires inside the loom. Rather, add two new twisted wires for the full length. One reason is YJ 258's have different color codes in the harness than CJ's. This will also leave it as close to the original as possible so future owners, or you, may change it back if this is desired. In this case, you could add two new twisted wires from the Ignition Module end to the Distributor end.

I did not do it this way. I went ahead and cut the wires at the firewall. If you prefer to do it the way I did, follow ahead. If not, perform the following steps by adding new wires end to end.

Step 5: Cut wires 3"-4" from the firewall. I brushed my unused ends with 3m electrical coating, then wrapped them in electrical tape just because I felt better about it rather than just leaving them exposed.

Step 6: Find the orange and purple wires at the ignition module (under the washer fluid reservoir). I had to remove my washer fluid and overflow reservoirs to get to the module.



Step 7: Cut the wires at the ignition module. I protected the unused ends here the same way as in step 4.

Step 8: Cut two lengths of extra 16 gauge wire to reach from ignition module to the firewall where you cut wires in step 4. Or to the distributor if you chose that method. Hint: If using the same color wire, mark each end of one as 'purple' and the other as 'orange'. Or, do as I did and simply color both ends of one wire, so you know which wire goes to which color once they have been twisted.

Step 9: Twist the two lengths of extra 16 gauge wire together just as the stock orange and purple wires are twisted. (This helps with insulation from outside electrical interferences). Hint: I read this trick elsewhere, and it really helped. Put one end of the wires in a 'C' clamp or something similar and the other end of the wires in an electric drill. Then twist. This made the process a lot easier. Twist until you meet about the same coil as the stock wires.

Step 10: Attach your extra 16 gauge wire from the orange at the ignition module to the orange from the distributor.

Step 11: Attach your other extra length of 16 gauge wire from purple at the ignition module to purple from the distributor.



Vacuum hose move. Steps 12-13

Step 12: At the carburetor, remove the vacuum line that is currently going to the distributor and plug the outlet you just removed it from.



Step 13: Find the ported vacuum line just behind the choke coil on the valve cover side of the carb and remove this line. Using a 'T', attach the distributor vacuum line to the other vacuum line you just removed.



Adjust timing to 8* BTDC. Steps 14-25

Step 14: Warm up the engine to operating temperature, then shut it down.

Step 15: Unplug the vacuum line at the distributor and plug it in.

Step 16: If using a timing light, follow the instructions to hook it up. Should be like this: Clamp the pickup onto the #1 plug wire, then hook up the negative lead to the negative side of the battery, then the positive to positive on the battery. Ensure no wires are in the way of fans, belts, or hot engine parts.

Step 17: Locate the timing marks on the front driver's side of the engine. The lowest mark is -2 degrees. You want the timing to be at the 6th markup. Each timing mark equals +2 degrees, counting up from the bottom.



Step 18: Loosen the bolt, which is below the distributor on the right hand side, slightly so you will be able to rotate the whole distributor.



Step 19: Start the vehicle.

Step 20: Take the timing light and aim it at the pulley to the left of the timing marks you found earlier. When the light flashes, you will see the notch in the pulley. You want it to be at 8* BTDC (+/- 2*). Check the timing marks on the front of your engine; however, on all in-line six cylinder engines, it should be the 6th markup.

To advance the timing move the ENTIRE distributor counter-clockwise. To retard the timing, go clockwise. DO NOT move the distributor by holding at the top. Move it from the bottom. You could get shocked otherwise.

Step 21: Turn the engine off.

Step 22: Lock the distributor in place by tightening the ½" bolt.

Step 23: Start the vehicle and re-check the timing. If it is of any, follow steps 18 through 22 again until it is right.

Step 24: Turn the engine off and clean up your mess, be sure to replace the vacuum hose you removed in step 15.

Step 25: Adjust the idle mixture screws on the front of the carb to the 'best lean' idle mixture and re-tune your carb.

Step 26: Enjoy a great running Jeep!!

Next for me...TEAM RUSH!!
 
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#2 ·
This is awesome...I wanted to do this while I was home to my new toy while I was on leave but didn't because I am not the smartest grunt in the world and I need pics. This thread will definately be saved for when I get home, and the madness will begin!!! Awesome post, and kudos to Mr Romain and the Arkansas Cheese Head!!!:thumbsup:
 
#8 ·
not really part of Nutter, but I also recommend remounting the ignition module up high on the passenger fender . It's much easier to work on, and it keeps the module cooler (and away from water).
OK...this brings me to my total nOOb question...I wanted to do this mod while I was on R&R leave, but I was unsure where the Ignition module is, or even what it looks like. Now I have a pic, but is it stock located on the driver or passenger side fender (I don't have a windshield wiper bottle in the veh to reference)? If it is on the driver side, how hard is it to relocate to the passenger side?
 
#6 ·
Great post and very helpful pictures. It's an easy mod but I still wish I had this post to reference when I did mine. Great job man.
 
#13 ·
I appreciate all the great responses. I was hoping it would come in handy. I know I really could have used something like this when I did mine!!! Like I said, though, I can't thank Mike enough for taking the time to work with me on this. Got to give him credit too!

I just thought for sure that by the time it reached 200 hits, someone would say "oh, you forgot this or missed this" but I'm am overwhelmingly suprised that hasn't happened yet.

Seriously though, if anyone does find something missing or screwed up, let me know and I can edit it.

Brian
 
#22 ·
Seriously though, if anyone does find something missing or screwed up, let me know and I can edit it.
Brian
Brian, great job. It should be a sticky. I would however also like to see before and after wiring diagrams side by side. It will give one an overview of the wiring they are changing.
A question about this mod. What are we actually doing? Since a carb is disconnected electrically, in what way are we changing the way a distributor operates. What was it doing that we stop or, what are we making it do that it didn't ?
Thanks again Brian, Mike, and all through history that have found out this secret big bang low bucks mod.
 
#15 ·
Are there any negatives to the nutter bypass?
Yes, it is technically illegal for street use because it disables emission controls.

Written the way John Nutter wrote it, it will also not pass emissions. Written the way luckycheesehead wrote it, it 'can' pass emissions.

The fact that it still passes the tailpipe emissions easily 'and' gets better mileage which is 'better' for the environment doesn't matter to 'some' emissions testers.

Here in Canada, every one I have done has passed emissions easily with numbers similar to mine: On the ASM 2525 test I got 589 NOx, 16 ppm HC and 0.11% CO.

Other than that, it just puts the engine in a 1981 or older state of tune, nothing else.
 
#16 ·
The reasons that Nutter posts are hard to find is that Nutter was pulling them. I guess it was so popular but illeagal that he was pressured into removing the posts/articals.

Some boards will not even let you post about removing and exhaust system or making any changes to the emmisions system. Try to ask about dropping the cat on the Quadratec forum and you'll bet hammered by the moderators. Seems like they don't want to run the risk of being party to anything illegal.

Even if it works and runs better with lower emmissions it's still illegal.
Fortunatly 25 years is the limit in my state for testing.
I wonder if I can still get in trouble if someone pulls me over for a vehical inspections. Techniclly I just don't have to get inspected. Nothing gives me permission to remove anything. Hmmm... I Know muffler shops won't touch my jeep.
 
#21 ·
The ground can't hurt.

And we want 'our' engines to run like 'yours' or pre 82 tune.
 
#25 ·
I bought my Jeep last April and with the electric control it ran like poop. Anyway to get what I'm asking I had got a pre-82 carb without the electric control and tuned it and it runs great passes emissions with flying colors. Now when I did that I didn't do the purple and orange wire part. Should I?
 
#26 ·
To the best of my knowledge, no. You did the modification the expensive way, by getting a new carb. The Nutter Bypass performs the modification the cheap way, by getting new wires.
 
#30 ·
The NUTTER BYPASS IS FOR JEEPS 1982 AND NEWER WITH THE BBD CARTER CARB. IT MAKES THE BBD CARB ACT LIKE THE 1970'S AND early 1980'S CARB THAT DID NOT LOOK AT THE ENGINE OPERATION TO ADJUST THE CARB SETTINGS

This is a nice write up on the Nutter ByPass!!

If the JEEP OWNER goes thru this, Nutter, upgrade or change I would also recommend upgrading the cap, rotar, coil, and plug wires. I noticed you pics used the OEM Jeep grey distributor cap. This change gave me 2.5 mpg inprovement with out changing a single thing. This is often refered to as TeamRush Upgrade. I STRONGLY RECOMMEND BOTH, NUTTER & TEAMRUSH.

TeamRush by JeepHammer
http://www.junkyardgenius.com/ignition/jeep/heicompair.html

Regards,
Fred
 
#32 ·
Quick question. I finally attempted the nutter / luckycheesehead bypass tonight and ran into an issue. When I went to disconnect the vacuum hose that runs to the dizzy, the other port at the "V" shaped tee was capped off also, but in the above pics, there appears to be a line running to somewhere. So I now have both of those ports capped off, but does the 2nd port need a line running somewhere?

Anyway, I moved on from that and finished the bypass, and I still couldn't really get the engine to hold an idle. I worked with the timing light to tell that I was keeping the rpm's at about 680 when I set it to 8 degrees. I plan on searching to try and find topics about setting the idle on the carb and all that, and I have the parts to attempt to do the Team Rich upgrade tomorrow, so I am just wondering if it sounds like I am on track, or should the Heep be keeping an idle better now with just that much done.
 
#34 ·
I have no first hand experience with the 4 banger but have 'talked' online with folks that have done it. They did not seem to have trouble.

The only gotcha is the ability to set the mix on the carb. I am guessing you have access to the carb mix screw down front or can get the cover/plug off it?

Other than that it was the same with the wires and the timing adjust needed. As I have mentioned here and there, i prefer to use two new wires when doing this job, rather than mess inside an old wiring harness.
 
#35 ·
Originally Posted by limegreenCJ7
Are there any negatives to the nutter bypass?


YES!!!!

ITS STILL A CARB!!!! Carbs became obsolete in the 70's, even the best carb cant handle rocky, bumpy steep inclines...which leads to stalls and restarts and broken parts! Do whatever it takes to get fuel injection!!! The difference will blow you away

Tom
 
#36 ·
Originally Posted by limegreenCJ7
Are there any negatives to the nutter bypass?

YES!!!!

ITS STILL A CARB!!!! Carbs became obsolete in the 70's, even the best carb cant handle rocky, bumpy steep inclines...which leads to stalls and restarts and broken parts! Do whatever it takes to get fuel injection!!! The difference will blow you away

Tom
LOL!

Properly tuned, the carb runs well enough for us, we run sand pit and ravine walls with our 258's and go until its so steep the tires start chewing in, while holding a 'nice' 450 rpm. Mine has never stalled from angles. My friends that have tuned their carbs with me around also run these pit walls and they don't stall out either.

You have to get the float right 'and' use two freaking wrenches when putting on the gas line so you don't wreck the float setting by compressing that easily compressed 'fat' gasket washer on the needle seat fitting the gas line screws into.

FI is also a compromise that cannot match a properly tuned carb for gas mileage. Yes, with gas prices like they are and the need to pass an emissions sniffer, my carb gets a major tune at least every two years so it gets 22 mpg highway (under 65 mph) and passes the emissions sniffer with low numbers.
 
#38 ·
I have the Chevy HEI distributor on my 258 already. I made that change so long ago that I can't remember what the original wiring looked like. The HEI has the purple and orange wires going from one part of the disty to another. I assume that one end of the wires go to the control module inside the disty. What part of the bypass wiring can I do with the HEI distributor installed? Does anyone know? I no longer have the old orange and purple wires from the firewall to the distributor.
 
#40 ·
ok...when i did this nutter bypass i ran into two problems i was missing 2 vacume lines so i only have the vacume from the distributer to the side of the carb, and those two biger ones on the same side of the carb...are the other two important? also my jeeps a 87 yj...could it be that its set up a litle bit differnt than the cj?
 
#42 ·
I also just bolted on a Ford 2bl Carb. does that allow me to eliminate the comp.??
I can't help on the gear but yes, the computer can now be put to sleep although why you would go with a Ford carb vs the Carter-Weber that was on there.....
 
#45 ·
The center post of the motor will move in steps. I think the right place for the pins is on the step that first captures the pins between the backboard and the side of the stepper motor. So when the board just goes below the lip, that should do it.

This should have the pins with their shoulder about 1/8" from the back wall.
 
#50 ·
I find that mid setting gives me and the folks I have helped a nice 21 mpg 'and' the emissions sniffer likes it there also. The fact the sniffer likes it and it gives a sweet top end response implies it sets the mix right. My plugs burn normal.

That mid setting has the shoulder of the pins sticking about 1/8" from the back wall when it is back together.
 
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