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Post-MC2150 swap: to Nutter or not?

3K views 37 replies 8 participants last post by  jth0033 
#1 ·
Hey all,

I performed the MC2150 carb swap last weekend. Everything went on flawlessly, I didn't have to adjust anything. Per the instructions (I bought it from the ebay guy), I hooked up the system to get it running, but didnt do the Nutter bypass (it says to get it running, do the bypass AFTER you make sure it runs/idles).

Anyway, I let it warm up and drove it around the block and at highway speeds. It drives perfect. No misfire, sputter, hesitation, etc. So my question is, do I need to do the nutter at all? I subscribe to the "if it aint broke, dont fix it" philosophy. I spoke to my mechanic buddy (a real, certified, mechanic...not shade tree) and he said if its running fine to just leave it alone. Always looking for second, third, or fourth opinions, I contacted the ebay guy. He said this:

"I have run many setups w/o doing the bypass, however... I still recommend it. It will eliminate the computer and problems down the road from the equation. I say do it."

What "problems down the road" is he referring to? I have the proper wires and also have a timing light, so I can do the bypass whenever. Basically, Im looking on what the cons vs. pros are in this matter. I havent been able to see what my MPG is with the new setup (since it was just installed and the jeep is a weekend vehicle), but I have noticed that throttle response, idle, and "powerband" is much better than the Carter. Plus, no more hard starting.

Thanks everyone!
 
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#2 ·
I switched out the distributer for an HEI one but before that I ran it without nuttering and I never had a problem. Either team rush or HEI, but upgrading the ignition is definitely your next mod.
I never worry about my comp now..in fact it is safe in a box in my garage:laugh:
 
#4 ·
Well, if you changed the carb, you pretty much de-smogged it also. So now you have a computer adjusting your timing with part of the system missing. Do you really think a computer like operating with missing data?

I'd nutter it, change the distributer to an earlier one (more advance in the distributer), remove all the computer wiring etc., and not look back. Anytime I can remove a possible issue to make trouble shooting other issues later on easier, I jump on it. Certified Mechanics like trouble shooting problems, they get good money doing it. Some mechanics won't work on modified vehicles, so, you are pretty much on your own, simplified it now is what I would do. Good luck with your project.
 
#5 ·
Well, if you changed the carb, you pretty much de-smogged it also. So now you have a computer adjusting your timing with part of the system missing. Do you really think a computer like operating with missing data?

I'd nutter it, change the distributer to an earlier one (more advance in the distributer), remove all the computer wiring etc., and not look back. Anytime I can remove a possible issue to make trouble shooting other issues later on easier, I jump on it. Certified Mechanics like trouble shooting problems, they get good money doing it. Some mechanics won't work on modified vehicles, so, you are pretty much on your own, simplified it now is what I would do. Good luck with your project.
Thanks Peter. I wasnt sure how much the computer really did, I was also curious about why some people Nutter and some dont (and never experience any problems).
 
#6 ·
Since you have the team rush upgrade, you are most of the way there. The distributer you might get is part number 30-4691 from advance auto on line about $70 I think. It will use all your team rush parts. I always take my old distributer gear off the old distributer and put it on the new distributor. Just so I don't have a new part wearing/breaking in on my old part. I sure most people don't do this, just be sure you get it on the right way. Mark the gear on the side the rotor is pointing to and put in on the new distributor the same way.

Take you time removing the computer wires. Open the harness and remove the wires one by one from the firewall end. You engine compartment will look a lot neater when it all done. Good luck.
 
#7 ·
Since you have the team rush upgrade, you are most of the way there. The distributer you might get is part number 30-4691 from advance auto on line about $70 I think. It will use all your team rush parts. I always take my old distributer gear off the old distributer and put it on the new distributor. Just so I don't have a new part wearing/breaking in on my old part. I sure most people don't do this, just be sure you get it on the right way. Mark the gear on the side the rotor is pointing to and put in on the new distributor the same way.

Take you time removing the computer wires. Open the harness and remove the wires one by one from the firewall end. You engine compartment will look a lot neater when it all done. Good luck.
I followed JeepHammer's 'how-to', since he did invent it ;) But, I didnt change the distributor or coil (he said I didnt have to). I still noticed a tremendous difference and even more so after the mc2150 swap. The only thing I didnt do was Nutter... thats why I posted this thread, Im on the fence on whether or not I should nutter now, wait and see, or not do it at all.
 
#31 ·
Just finished my Nutter (well, earlier today). Monkeyhouse and the others are totally right, its worth it. I hate to get on the "its awesome" bandwagon before Ive put some road miles on it, but having driven it around the block a few times after, I have to say I notice a difference.

I also talked to the ebay guy about how I hooked up my carb and found out I had some stuff off. Got that corrected and done the bypass...seems to be running better than ever now.

As far as timing, its pretty straight forward. Get a timing light and a distributor socket/wrench if you dont have them already to make your life easier. This was the how to I followed: http://www.jeepforum.com/forum/f8/how-nutter-bypass-522262/. The hardest part for me was actually cutting the wires to get the whole thing started... to much anxiety over that haha. Once I bit the bullet, it all was pretty straight forward.

It turned out for me that it ran better by advancing the timing just a little than the recommended 8*TDC, but it also says +/-...I fell into the + category

Thanks everyone for their input and help. If I remember, Ill post up again in a week or so to give everyone an update on how she's running :cheers2:
 
#9 ·
jth0033 said:
I just completed my motorcraft swap and haven't done the Nutter yet. Interested to see what everyone says about it. I want to do it, but have never done timing stuff so I'm afraid to adjust it and mess something up.
That's why I posted. I'm sure I'm not the only one wondering :)

I've never adjusted timing either and I don't want to do something that isn't going to make a tremendous difference. "not broke, don't fix it"
 
#10 ·
Since you did the carb and the Rush your computer really doesn't have much to do anyway.
It can't materially effect the timing, just the dwell. In Jeeps of our age the only inputs are vacume and O2. not throttle, crank, temp or anything really technical.
Put it out of it's misery and you will have one less thing to worry about.

Computers are for fuel injection and distributerless ignitions anyway.
 
#11 ·
vadslram said:
Since you did the carb and the Rush your computer really doesn't have much to do anyway.
It can't materially effect the timing, just the dwell. In Jeeps of our age the only inputs are vacume and O2. not throttle, crank, temp or anything really technical.
Put it out of it's misery and you will have one less thing to worry about.

Computers are for fuel injection and distributerless ignitions anyway.
I've looked on here for a picture guide on how to do the nutter. The most definitive has the pictures removed for some reason. Do you know of another one?

The one on here shows you cutting wires (purple and orange) at the ICM. Another thread says to SPLICE into the purple wire. Which is correct?
 
#12 ·
Go to the FAQ's. Under engine/carb swaps there are three writeups on doing the nutter. The only reason most people do not do the nutter is because they have to pass emissions testing. The nutter bypass is a simple thing to do, people who are scared to death to work on engines do it and are happy they did. If you can swap a carb, you can definitely check timing. Go to autozone, they have a timing light there for 40 bucks. Everyone should feel comfortable checking their timing. It's easy and you will feel better knowing what it's set at. And you are cutting and splicing. You are really just cutting the computer out of the mix. Now both of you get out there and do the nutter! lol.
 
#13 ·
monkeyhouse said:
Go to the FAQ's. Under engine/carb swaps there are three writeups on doing the nutter. The only reason most people do not do the nutter is because they have to pass emissions testing. The nutter bypass is a simple thing to do, people who are scared to death to work on engines do it and are happy they did. If you can swap a carb, you can definitely check timing. Go to autozone, they have a timing light there for 40 bucks. Everyone should feel comfortable checking their timing. It's easy and you will feel better knowing what it's set at. And you are cutting and splicing. You are really just cutting the computer out of the mix. Now both of you get out there and do the nutter! lol.
I have a timing light, 16 ga orange and purple wires (10'), wire cutter/strippers, and a 16ga splice. I have to replace the clutch master cylinder this weekend & I'll prob go on and nutter to since I have it all. I can always reverse it if something goes wrong (haha I hope).
 
#15 ·
Ok, now I understand a little better what you are asking. No, nutter will not make a tremendous difference if it's running to your satisfaction right now. People that have done the nutter and added the better distributor have noticed a difference. I know I sure did, I would not say a tremendous difference, but, I would not go back either. My main reasons were to remove the 25 year old connectors and replace them with new GM Weather Guard Connectors, inspect/update the wiring, remove items that can cause problems down the road with no benefit now, and to have components they were designed to work together i.e. simple carb, simple ignition system, simple charging system etc. These are simple engines that were burden with stop gap measures to make them meet smog laws. Sometimes not too effciently. I very pleased with the way it runs now, and not so much before.
 
#16 ·
Peter Nuss said:
Ok, now I understand a little better what you are asking. No, nutter will not make a tremendous difference if it's running to your satisfaction right now. People that have done the nutter and added the better distributor have noticed a difference. I know I sure did, I would not say a tremendous difference, but, I would not go back either. My main reasons were to remove the 25 year old connectors and replace them with new GM Weather Guard Connectors, inspect/update the wiring, remove items that can cause problems down the road with no benefit now, and to have components they were designed to work together i.e. simple carb, simple ignition system, simple charging system etc. These are simple engines that were burden with stop gap measures to make them meet smog laws. Sometimes not too effciently. I very pleased with the way it runs now, and not so much before.
I did the team rush weekend before last. It was nice, but it still sputtered. I than did the carb swap and it was like a new engine. I'm happy thus far with the result. I didn't nutter, because of the above mentioned reasons, but I suppose I will to see if it makes it that much (or even a little) better.

I want the engine to run at it's max efficiency and performance. I know it's not a sports car, but I want smooth acceleration and no "poppin'-n-snappin'" at higher rpm. I was curious about the downside to nuttering, if there were no issues right now with it. Or, what those issues COULD be down the road from doing it or not :)
 
#19 ·
Your mechanic buddy is spot on in that the micro computer would control timing and I'll add with regard to retard as well as advance. I say would since having removed one of the most important being the BBD, of the 11 total components in that loop of input and to output signals. As it is now the computer is stuck in open loop in the start up or possibly the warm up phase.

And in regard to your buddy saying the computer was important, again he is spot on, it was, just as long as all of those components were functioning as intended. The so called 'team rush' Ford big cap upgrade had zero effect on the computers function but the carb change did.

Do the bypass.
 
#20 ·
Given the age of the YJ, I doubt it was working like it was supposed to. I found vacuum lines that had been eliminated (just hanging loose) and others that were capped. Im sure all that totaled up to performance robbing. Since Ive Team Rushed and done the MC swap, Ive noticed gains in power and throttle response (not to mention better idling and better RPM range). I havent tested the MPG because of all the idling Ive done while working on it, it wouldnt be fair to assess that right now, but my guess is it'll be slightly better.

I discovered my clutch master cylinder had a small leak, so Im changing that this weekend and doing the nutter to. She'll be like a whole new jeep :2thumbsup:
 
#21 ·
Ok, I want to make sure I have the nutter steps:

1) trace orange & purple wires from distributor up firewall
2) cut wires a few inches from firewall
3) find orange and purple wires at icm
4) cut orange wire at icm; splice into purple icm wire
5) connect orange wire from distributor to orange icm wire
6) splice (not cut) purple distributor wire into purple icm
7) time distributor to 8* TDC

Did I miss anything?
 
#22 ·
you are making it way to complicated. You do need to trace the wires, just to make sure they don't change colors anywhere. All you are doing is cutting the wires coming from the distributor and the wires coming from the icm and taking two pieces of wire and connecting those wires. Most people have orange and purple at both ends, a few do not.
 
#23 ·
monkeyhouse said:
you are making it way to complicated. You do need to trace the wires, just to make sure they don't change colors anywhere. All you are doing is cutting the wires coming from the distributor and the wires coming from the icm and taking two pieces of wire and connecting those wires. Most people have orange and purple at both ends, a few do not.
Thats sorta what I said :)

I saw two different write ups. One says to cut the purple icm wire, another says to splice the purple wire. I just wasn't sure which was (or if both were) right. I'm going to attach the wires near the firewall to keep things tidy.
 
#26 ·
Cut the wires. Don't splice in.

My 1990 was orange and purple on each end. I didn't follow them, if it is the twisted pair, you know you have the right ones.
you might wanna do some more research. Basically you got lucky. There is a reason they said to follow the wires through the loom. Carelessness is never gonna be the best policy, especially with vehicles with several owners over 20 or so years.
 
#27 ·
I've opened up the loom since then. There is only one set of twisted wires. Even without the color coding, you can tell which are which from where they originate from.

There isn't any reason to open up the loom if you don't want to, unless you aren't sure what you are looking at.
 
#29 ·
monkeyhouse said:
you might wanna do some more research. Basically you got lucky. There is a reason they said to follow the wires through the loom. Carelessness is never gonna be the best policy, especially with vehicles with several owners over 20 or so years.
I think in some yj's the wires can change from orange and purple to another color (green comes to mind for some reason).

Thanks all for clearing up that you cut the purple icm wire instead of splice. I figured It made more sense to cut it, but I've never done this before :)

I'm going to use weather resistant butt connectors and heat shrink to tidy up and connect the wires.
 
#33 ·
Of the mc2150 or what exactly?

The Nutter was done by step by step from the link I posted earlier. The Team Rush upgrade was done by the write up that JeepHammer had done. Pretty much all my upgrading was done via JeepForum threads. For that, I plan to join as a supporter ASAP :2thumbsup:

If you need photos of the MC setup, shoot me your email and Ill email them to you, with as much detail as I can. I also plan to post up a write up on what the final MC2150 should look like, once Im certain that its how its supposed to be. The ebay guy has been indispensable with my questions! Some say that he charges to much for his carbs, but it was money well spent in just having some one I could email/call to get my YJ running like new again. I thought it ran great when I got it, but that was nothing compared to now.
 
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