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Thumper gets another Mod

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AKoller View Drop Down
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    Posted: 09 Mar. 2020 at 9:21pm
For the last 3 years I have been fighting the Rochester 2 Jet that was on the Dauntless V6 in Thumper. It would always run great on the road but when I get it on the trail I could never get it to run how I would like when I got into off camber situations. I honestly felt it was unsafe the way it was for the fact I sometimes have a tendency to get myself into precarious situations and then it dies. Sometimes it would refire sometimes not. I've been told that it was one of the finest off-road carburetors ever made but I just never found that to be the case.

Well after trying everything under the sun to try to get it to run how I would like off-road I finally decided enough is enough. I decided to install a Motorcraft 2150 with Metcalf's "off-road kit". I know this isn't anything new and many of you guys running Dauntless engines already done this. I couldn't find much information about this swap online so I thought I would record my experience with it here.

I started with ordering a cheap knock off 2150. A good (not wore out) OEM unit is just really hard to find and from what I've read people have had good luck with these import units.



I removed the old Rochester and bolted on the RPC adapter (P/N R2086). I found that the exhaust ports that run to the base on the 2 Jet on the stock Dauntless intake manifold were going to be an issue. By leaving it how it was it would blow exhaust up into the carb because the adapter plate didn't block off the ports all the way off. I drilled and tapped the ports to 1/4" NPT and installed pipe plugs (I forgot to take pictures of this step.) Once done with this I reinstalled the adapter.



After getting the 2150 mounted in place, fuel lines run, choke and throttle hooked up I found that the power valve cover was touching the thermostat housing on the intake. The 2150 came with the deep cover to accommodate a 2 stage power valve. So I had to find a 2100 power valve cover so I would get the clearance I needed.







After going for a drive I found the power valve wasn't correct. It would idle fine and once I got to speed it would run fine but it would fall on it's face during acceleration. After running a vacuum test at the intake I figured out what power valve I needed. After installing the correct power valve it runs out great. By reading the exhaust and plugs I feel like I'm really close on jet size. To be sure I figured I would order a wide band gauge. It should be here later this week.

I went out and did some testing on Saturday around my property and put Thumper on some angles that were frankly kinda scary in order to try to see if I could get the carburetor to have any hick ups. It ran perfect the whole time. Next month it will get a real test at The Willys Rush @ Rush Springs Ranch.



1950 CJ3A "Thumper"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote NCtoy Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 1:36am
Do you have the part number for the power valve you used? I saw your other post on Facebook and was hoping for some under hood pics. Does it run different overall, or is it only really noticeable on steep terrain?
My 2g hasn’t had much trouble running on angles, but it has something of a dead spot just off idle that I can’t seem to get rid of. Maybe a carb swap is the best solution, although it kind of seems like giving up. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 12:10pm
Originally posted by NCtoy NCtoy wrote:

Do you have the part number for the power valve you used? I saw your other post on Facebook and was hoping for some under hood pics. Does it run different overall, or is it only really noticeable on steep terrain?
My 2g hasn’t had much trouble running on angles, but it has something of a dead spot just off idle that I can’t seem to get rid of. Maybe a carb swap is the best solution, although it kind of seems like giving up. 


The overall on road performance has changed. It is noticeably more responsive and I feel like it has a bit more power.

The power valve will vary from engine to engine. To find the correct one you'll need to get a vacuum reading at the intake manifold. This is done at idle. I had 18" of vacuum at my intake. So I took 18 divided by 2 is 9. Power valves only come in .5 readings so you drop down to the next lower .5. So I purchased a 8.5 power valve. I hope that makes sense.

The vacuum reading will also change at different elevations. The greater the elevation the lower your vacuum will be. When I take Thumper to Colorado this summer I will need to do this again and install the correct power valve for the elevation. I know guys that are running the Motorcraft that don't do this and they do fine though they are probably giving up some performance.

Here is an under hood look at it now with the new carb. I had to overhaul the air cleaner where it mounts to the carb to fit the larger diameter.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jpet Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 12:25pm
Very cool!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepFever Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 12:51pm
  .
Nice writeup ! . .  I had not heard of this swap before you mentioned it. 

After first post,  I was going to ask what you plan for air cleaner,  but I see you answered that question since I was last in here. Smile  Where did that come from?      How tall is the new carb arrangement,  including adapter?

The 2GC on mine seems to be working well these days.   I used to have an intermittent off-idle dead spot.  (not during acceleration,  but just a position of throttle that would run crappy).   After installing electric choke,  that went away.  I think the heat-riser choke had some kind of vacuum leak maybe?

As you say though,  I might not know what I am missing.  

Thanks for posting this,  it will be a goto one day. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 1:16pm
Originally posted by JeepFever JeepFever wrote:

  .
Nice writeup ! . .  I had not heard of this swap before you mentioned it. 

After first post,  I was going to ask what you plan for air cleaner,  but I see you answered that question since I was last in here. Smile  Where did that come from?      How tall is the new carb arrangement,  including adapter?

The 2GC on mine seems to be working well these days.   I used to have an intermittent off-idle dead spot.  (not during acceleration,  but just a position of throttle that would run crappy).   After installing electric choke,  that went away.  I think the heat-riser choke had some kind of vacuum leak maybe?

As you say though,  I might not know what I am missing.  

Thanks for posting this,  it will be a goto one day. 


The air cleaner is from the first generation Ford Bronco with a V8. It works well where hood clearance is an issue. Plus it looks cool.

The new carb with the adapter combination is the same height as the 2Gc Rochester I took off if not maybe just a little shorter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nothing Special Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 4:46pm
I need to get one of those air cleaners for my Early Bronco with a V8 (Bronco people don't use the "first generation" designation)

I was going to post that I've got an Autolite 2100 on my Bronco and it works great.  The exhaust smells like unburned gas when driving it over Black Bear pass, and I'm sure I'm giving up some power.  But with no adjustments it works smooth from 700' elevation where I live up to over 12,000'.  And no issues on rocks either.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepFever Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 5:06pm
My son has 2100 or 2150 on his CJ-7 with 360 v8.    It has always done very well offroad,  in rocks/hills etc.

How can you tell difference between 2100 and 2150?   I tried to do a quick search,  but need to get back to work Cry.    Sounds like there are a bunch of different versions of both.   Even different venturi sizes!  

I have two carbs at home,   I always thought the one with small third "venturi" in center was a 2150, and other was 2100,  but maybe not.      I looked briefly last night,   but could not find 21xx anywhere on these carbs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 5:11pm
Originally posted by Nothing Special Nothing Special wrote:

I need to get one of those air cleaners for my Early Bronco with a V8 (Bronco people don't use the "first generation" designation)


There is one listed on Ebay right now with a buy it now price of $85.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 5:27pm
Originally posted by JeepFever JeepFever wrote:

My son has 2100 or 2150 on his CJ-7 with 360 v8.    It has always done very well offroad,  in rocks/hills etc.

How can you tell difference between 2100 and 2150?   I tried to do a quick search,  but need to get back to work Cry.    Sounds like there are a bunch of different versions of both.   Even different venturi sizes!  

I have two carbs at home,   I always thought the one with small third "venturi" in center was a 2150, and other was 2100,  but maybe not.      I looked briefly last night,   but could not find 21xx anywhere on these carbs.


Someone please correct me if I'm wrong but I am with the understanding that the 2150 replaced the 2100. They are essentially the same thing with the difference being the 2150 had changes done to meet emissions standards. I actually "deleted" some of the emissions items off of my 2150 I installed.

As far as venturi sizes go, I think the 2100 was offered in 4 different sizes. I went with the 1.08" venturi. Once again someone needs to correct me if I'm wrong.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepFever Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 8:21pm
According to one guy,   the quickest way to identify is the bottom surface.

The 2100 is curved:




The 2150 is straight




He also mentioned the power valve covers,   but said that is not sure-fire,  because sometimes they get swapped. Wink  LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JeepFever Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar. 2020 at 11:54pm
Checked out my carbs,  and both are 2150 based on the straight edge.



The one on the left in these photos has the "altitude compensation" feature.  It came from a '79 Cherokee I think.  It has the 121 venturi

The one on right is from '77 Cherokee I think,  It has the 108 venturi.  It is in better condition,  so would most likely be the best choice for a swap.



It is not important what I have,   but thought it might be interesting to show just 2 of many variations of this model carburetor.    Are there any things to look for?  that are either desirable,  or not?



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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 11 Mar. 2020 at 12:26am
I would use the 1.08 Venturi carb myself. They are rated at 287 cfm whereas the 1.21 is rated at 351 cfm. I could be wrong but that seems like it a bit much for a “stock” built Dauntless.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar. 2020 at 12:14pm
The wide band gauge I ordered showed up in the mail yesterday. With any luck I will get it installed sometime in the next week. It will be nice knowing for sure if my jetting is right. Like I mentioned in an earlier post I feel like I'm real close by reading the plugs and exhaust. This will tell me if I'm any good at checking the air/fuel mixture the "old school" way.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote drm101 Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar. 2020 at 1:34pm
The gage and o2 sensor seems reasonably priced. $124 with the weld on bung and they offer different colors. Thanks for the info!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 18 Mar. 2020 at 8:30pm
Good stuff Alan. It makes me happy to see you happy.

If anyone has any questions let me know. I will try and help where I can.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote AKoller Quote  Post ReplyReply Direct Link To This Post Posted: 13 Apr. 2020 at 1:36pm
A few days ago I decided to try and get this wide band gauge installed. In order to put the O2 sensor in the exhaust you have to weld in a treaded boss. According to the directions they want it welded in somewhere between the 10:00 and 2:00 position on the pipe. There is just no way in could get in to weld it with the exhaust in the Jeep. So I dropped the exhaust out and welded the boss in.

While the exhaust is out I decided this would be a great time to wrap it with header wrap to try to minimize heat transfer through the floor. So I ordered some header wrap and am now playing the waiting game.




Another thing I've been wanting to experiment with is removing some of the leaves out of my spring packs. I am running the Superlift 2.5" lift springs and they are STIFF!

After seeking some council from Rick G last fall I decided to remove the 2 shortest leaves. I believe that's what he did on Gus and he says it helped. It was actually a much easier job than I had anticipated. Start to finish it only took less than 2 hours. I do think I may have lost about 1/4"-1/2" of ride height. That is not a huge concern of mine since I got rid of my 33x12.50s and went to the 7.50x16s. I have lots of clearance.

Before doing this if I would bounce my body weight up and down while standing on the bumper it would only move about and inch. Now it moves way more and feels much softer. Once I get the exhaust put back on I will take it for a test run to see how it does.





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Metcalf Quote  Post ReplyReply Direct Link To This Post Posted: 13 Apr. 2020 at 6:32pm
I do wonder how the spring pack will hold up with the leaves removed.

I was surprised how fast my 1" Superlift springs sagged over a few years. I can't really complain with how much they cost at $84 per pack shipped. For that price I would buy more if they still made them.  I'm tempted to use a 2.5" spring with a 1" lowering block to start.....then pull the lowering block out after a few years once the springs sag.




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