CJ7 Overwhelming Exhaust Smell - JeepForum.com
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post #1 of 18 Old 05-15-2019, 06:04 PM Thread Starter
gkoz19
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CJ7 Overwhelming Exhaust Smell

I installed a Motorcraft 2150 carb on my 1986 CJ7 and the exhaust smell is overwhelming, which leads me to believe it's running rich. I've troubleshooted the things below and at this point I'm not sure what else it could be. It idles and runs fine, the spark plugs are a bit black.

-Motorcraft 2150 bought brand new on eBay
-Performed Nutter bypass
-Adjusted timing with timing light
-Adjusted idle adjustment screws with vacuum gauge
-No exhaust leaks
-Currently has .48 main jets, I tried .46 but it ran like crap
-Exhaust exits rear driver side corner and is angled 45 degrees down

I bought it from California, so I'm not sure if something emissions related is causing it? The Jeep was a mess when I got it, there were many things that are plugged or cut that I tried to fix as best I could. This is my first CJ.

Any help or ideas are appreciated. I'm located in Cleveland, OH.

Thanks,
Greg

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post #2 of 18 Old 05-15-2019, 10:22 PM
Eazyrider805
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Is it like a raw fuel smell or Exhaust smell? I know you stated that it is an exhaust smell but being that you just installed the carb makes me wonder. When I used to work on motorcycles a good way to tell if their was an exhaust leak is to spray soapy water on the exhaust to see if it bubbles might help isolate the cause. I am from CA and its a pain to have these vehicles smogged. I dont know what the laws are in Cleveland but maybe try to remove the smog equipment or work around it? I bought my CJ7 with the Howell fuel injection on it already due to the fact that of the SMOG laws in CA. I would highly recommend the Howell fuel injection kit if you get sick of trying to tune and mess with the carb.

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post #3 of 18 Old 05-15-2019, 11:03 PM
BagusJeep
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It was a 1986 so was CEC computer emissions. A real mess normally.

So you have Nuttered and replaced the Carter BBD feedback carb with an MC, a common upgrade.

Have you changed the vacuum hoses to a simpler design? I see a large red hose in the pics, not sure where that is going. The dizzie vacuum advance will run best on manifold vacuum, not the ported vacuum it had in 1986.

The distributor also needs some work, the mechanical advance in 1986 was limited to 6.25 degrees as the CEC computer controlled the rest. This would benefit from being 13 to 18 degrees. Look up how to open up the dizzie and flip the advance head and it will run better.

The ignition system needs to be in tip top condition. If you have an old set of leads and cap etc consider the Teamrush upgrade when you come to do a tune up. The larger dizzie cap etc. will get a cleaner spark. I did have Jag V12 cap crack which sent soot out of the exhaust, these things need maintenance.

Are you using a mechanical or an electric fuel pump?

Did you adjust the carb floats etc before installing?

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post #4 of 18 Old 05-16-2019, 10:25 AM Thread Starter
gkoz19
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Quote:
Originally Posted by Eazyrider805 View Post
Is it like a raw fuel smell or Exhaust smell? I know you stated that it is an exhaust smell but being that you just installed the carb makes me wonder. When I used to work on motorcycles a good way to tell if their was an exhaust leak is to spray soapy water on the exhaust to see if it bubbles might help isolate the cause. I am from CA and its a pain to have these vehicles smogged. I dont know what the laws are in Cleveland but maybe try to remove the smog equipment or work around it? I bought my CJ7 with the Howell fuel injection on it already due to the fact that of the SMOG laws in CA. I would highly recommend the Howell fuel injection kit if you get sick of trying to tune and mess with the carb.
It's hard to describe, but I'd say more of an exhaust smell than raw gas. My clothes are saturated in the smell if I drive with the top down. Since it's over 25 years old, I do not have to get an emissions test done, thankfully. Rather not spend the money on the fuel injection kit, but may have to resort to it down the road.
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post #5 of 18 Old 05-16-2019, 10:31 AM Thread Starter
gkoz19
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Quote:
Originally Posted by BagusJeep View Post
It was a 1986 so was CEC computer emissions. A real mess normally.

So you have Nuttered and replaced the Carter BBD feedback carb with an MC, a common upgrade.

Have you changed the vacuum hoses to a simpler design? I see a large red hose in the pics, not sure where that is going. The dizzie vacuum advance will run best on manifold vacuum, not the ported vacuum it had in 1986.

The distributor also needs some work, the mechanical advance in 1986 was limited to 6.25 degrees as the CEC computer controlled the rest. This would benefit from being 13 to 18 degrees. Look up how to open up the dizzie and flip the advance head and it will run better.

The ignition system needs to be in tip top condition. If you have an old set of leads and cap etc consider the Teamrush upgrade when you come to do a tune up. The larger dizzie cap etc. will get a cleaner spark. I did have Jag V12 cap crack which sent soot out of the exhaust, these things need maintenance.

Are you using a mechanical or an electric fuel pump?

Did you adjust the carb floats etc before installing?
I haven't changed the vacuum, but will look into making it simpler.

Haven't messed with the distributor, but will make these changes.

Not sure on the fuel pump.

I did not adjust the float, but will research that too.

Thanks for the suggestions. I'll report back soon hopefully.
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post #6 of 18 Old 05-16-2019, 11:37 AM
John Strenk
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You might need a new air filter.

If you can find a different housing to hold a larger air filter, that might be a good idea.
You don't have power brakes so it might be rather simple.

Definitely look into upgrading the distributor to a TEAM RUSH configuration. This will give you a better spark making for a more complete burn.
To make it real simple, look into a GM HEI conversion. I think they run anywhere for $100 to $300 but having a good ignition system make tuning so much easier.

If you don't have a good spark, it's hard to make carb adjustments work.


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post #7 of 18 Old 05-16-2019, 01:25 PM
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post #8 of 18 Old 05-16-2019, 02:28 PM
uptillnow
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I was looking at my notes, when I worked on a few of these 2100/2150's.

1.08 venture #47 jet (1.08" x 25.4 = 27.43mm venture)
1.21 venture #46 jet (1.21" x 25.4 = 30.73mm venture)
6.5 power valve @ 3000 ft and up
7.5 power valve up to 3000 ft
the power valve choice was estimated at 80% of the driving at these altitudes, seemed to work well. This is my guide for jetting the Motorcraft, more High Performance modifications take more fuel...

The simplest/best upgrade for your timing/ignition issue is the H.E.I. distributor. ($100.00 to $300.00) You would get a normal advance curve, rather than an emissions total advance curve of 6.5 degrees like Bagus Jeep stated, better starting, better acceleration, more power, etc..

The cheapest way to get a more normal centrifugal advance is to change/turn your advance head in your Motorcraft distributor. I stole these pictures from Matt, and have used them many many times explaining when you take the computer out of adjusting the timing (Nutter by-pass) you are left with very little total timing. We "flip" the advance head to the 18R slot. This gives about 18 degrees of advanced timing position. You still have the Duraspark ignition, but with the "Team Rush" upgrade and flipping the advance head you will have reasonable timing throughout your RPM range. Take a look in the "PEEP" hole to see what advance slot you have.
Check these pictures out...
UTN
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post #9 of 18 Old 05-17-2019, 08:07 AM
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Quote:
Originally Posted by gkoz19 View Post
It's hard to describe, but I'd say more of an exhaust smell than raw gas. My clothes are saturated in the smell if I drive with the top down. Since it's over 25 years old, I do not have to get an emissions test done, thankfully. Rather not spend the money on the fuel injection kit, but may have to resort to it down the road.
Where does your exhaust exit your Jeep? If it comes out the back and not the side behind the driver's side rear wheel you are sucking the fumes inside the Jeep. I also agree with John about the air cleaner. Driving with a dirty air cleaner is like driving with a choke engaged.

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post #10 of 18 Old 05-17-2019, 05:51 PM
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my 76 had exhaust smell pretty bad , I ended up adding a good 8" to the length to get rid of it. Right now it is down at a 45 and about 7" past the rear of the body. ANd no more smell.
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post #11 of 18 Old 05-17-2019, 06:59 PM
terre
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sealed the tailgate

I had the same issue, with the the top all secured down and the windows zippered shut for winter. Installed some window seal foam strips in between the tailgate and tub. Took 90% of it away. With the windows and doors off I still get some exhaust inside. Kind of a band aid to a more deeper issue. It was interesting to note the above entries on the spark, carb and advanced corrections that will help burn the gas more completely.
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post #12 of 18 Old 05-18-2019, 07:18 AM
Shawn Watson
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What are the mixture screw limits compared to where yours currently are?

The reason I ask is that on a Weber, if you're lean on the idle jets and drawing from the progression circuit at idle, it'll stink up both yours and your neighbor's house with that noxious, eye-burning smell.

Does a Motorcraft have transition slots that can be diagnosed like a Holley by flipping the carb over to see how much of the slot is exposed below the throttle plates?


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Last edited by Shawn Watson; 05-18-2019 at 08:30 AM.
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post #13 of 18 Old Yesterday, 07:08 AM Thread Starter
gkoz19
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Quote:
Originally Posted by uptillnow View Post
I was looking at my notes, when I worked on a few of these 2100/2150's.

1.08 venture #47 jet (1.08" x 25.4 = 27.43mm venture)
1.21 venture #46 jet (1.21" x 25.4 = 30.73mm venture)
6.5 power valve @ 3000 ft and up
7.5 power valve up to 3000 ft
the power valve choice was estimated at 80% of the driving at these altitudes, seemed to work well. This is my guide for jetting the Motorcraft, more High Performance modifications take more fuel...

The simplest/best upgrade for your timing/ignition issue is the H.E.I. distributor. ($100.00 to $300.00) You would get a normal advance curve, rather than an emissions total advance curve of 6.5 degrees like Bagus Jeep stated, better starting, better acceleration, more power, etc..

The cheapest way to get a more normal centrifugal advance is to change/turn your advance head in your Motorcraft distributor. I stole these pictures from Matt, and have used them many many times explaining when you take the computer out of adjusting the timing (Nutter by-pass) you are left with very little total timing. We "flip" the advance head to the 18R slot. This gives about 18 degrees of advanced timing position. You still have the Duraspark ignition, but with the "Team Rush" upgrade and flipping the advance head you will have reasonable timing throughout your RPM range. Take a look in the "PEEP" hole to see what advance slot you have.
Check these pictures out...
UTN
I flipped the advanced head in the Motorcraft distributor to 18 degrees and performed the TeamRush upgrade. What a difference! Runs smoother and the exhaust smell is significantly reduced. I no longer smell like a lawn mower after driving it.

Thank you all for your feedback and help.


-Greg
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post #14 of 18 Old Yesterday, 10:58 AM
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Greg,

Glad to hear your advance slot change over to the 18R slot was so successful.

I have a friend in Utah at 8500' who I talked into flipping his advance head to the 18R slot. He was so excited with the results, he went to many of his CJ-YJ friends and flipped their advance head as well. Then, he thought because of his altitude, he pulled his distributor apart again and filed one side to advance even more than the 20 degrees total advance from "HIS" 18R slot. He runs 22 degrees at 8500 feet and is very happy. He didn't think this would change things very much and is pleasantly surprised.

I want to add here that "I" have never seen a 6.25 to 6.75 slot in a Motorcraft distributor. The only ones I have seen in Jeeps are the 13R / 18R advance slots. And the 13R slot is where the advance arm operates it's 13-14 degrees mechanical/centrifugal advance. This changing slots is a huge difference in timing for economy and all around performance gains.

And, that all being said, running manifold vacuum advance will increase the idle speed which will allow you to close the throttle plates with your idle speed screw.

A major improvement in centrifugal advance and actual spark energy increased over the Duraspark ignition is the HEI distributor. Just sayin

UTN
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post #15 of 18 Old Yesterday, 11:23 AM
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Quote:
Originally Posted by uptillnow View Post
...
A major improvement in centrifugal advance and actual spark energy increased over the Duraspark ignition is the HEI distributor. Just sayin

UTN
And you won't accidentally burn up your ICM by listening to your radio with the engine not running. Yes, there is a Accessory position on the ignition switch but probably most people don't know it.

The HEI shuts itself off when the engine stops. The DuraSpark keeps on putting out power, overheating the coil or burning out semiconductors in the ICM.
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