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Discussion Starter · #1 ·
Hi guys,

Yeah, I own an 89 Jeep 258, lol. I have gained a TON of information lurking in here and other forums and sites. Please don't take this post as a grab and go. If anything, take it as a Compliment, IMHO, you cats seem to be the authority on Webers. I've gained knowledge, from 280Z, BMW2002 and other forums as well, but nothing like here. One fellow in particular in here, actually inspired me in some ways, @RallyBob if he's still around. I do not own an Opel, wouldn't mind one, certainly cool!!! But 1 look at a GT and BMW 2002, too rich for my blood, sadly.

Anyhow, us YJ and CJ guys tend to buy Webers (32/36 and 38/38's), well, very few know much about them it seems. They'd rather complain and not dive deep to learn them and tune them. I have dove deep into this realm, couldn't tell you squat about a Motorcraft or Holley, lol. But I know about DCOE's, DGAS/DGES, IDF's and more now. I actually made a 38/38 Progressive carb a couple of weeks ago mating some parts together. Not gonna lie, smoothest running carb I think I've ever felt, felt like a single barrel in continuity, but double barrel in performance, hopefully that makes sense, lol.

So know that I'm out as a totally different bird, lol, I'm hoping you guys could help me out.

In looking at tech manuals, the kit that is broadly sold here in the US uses 38/38 barrels with a 27mm Venturi, this doesn't quite match up with the Weber sizing of "Main Venturi x 1.25", but ok. Maybe because our intake doesn't accept larger than a double 38mm? I've thought about "fixing this" (the Rally Bob guy I spoke of eariler?), but I can't go back if I do-comments/insight appreciated. Anyhow, no biggie, I got what I got for now, but we are LOW RPM engines. We don't rev past 3,500 usually, 5k RPM and you should have a kevlar vest on..... to that point, the next calculation is "main Venturi size x 4 = Main Jet". This would put us at 108 Main Jet (give or take), and a 160 (give or take) air corrector. My best performance with an LM-2 AFR (I told you I dove deep) and logging was with a 150 Main Jet and 170 Air Corrector.

I have the loggings, but at home, and not there new-car post if interested. I was around 10.0-11 AFR (used 14.1 AFR for 10% Ethanol blend-I'm chasing low RPM TQ) and when I had the 190 Air Corrector would get heavy lean spikes. I know lean spikes can be normal for no throttle, etc but I was getting them at high RPM, and super lean, like 22 AFR spikes. Switch to 170 Air Corrector, and MUCH better. But I'm only at a .030 difference, not the 40 between Fuel/Air Corr jets, that Weber suggests, what gives? I have also been using 4.5mm Aux Venturis. Ditched the 4.0mm, they kept it LEAN, and when I say lean, I mean lean!! My Accelerator pump is still the 50, maybe 55?, I tried the 70, it dumped too much gas when I got on throttle, I want rich TQ, but it was stumble type rich.

One more question, if you don't mind, when the charts, like this one...
Rectangle Font Line Parallel Slope


Are used, would I be correct in assuming that a 4.2 L, 4200cc engine with 2 barrels (1 38/38) actually should be read as 2100 CC @4k RPM (my engine) for the Venturi size? So my Jeep should actually be at around 33mm or so main Venturi? Again, back to possibly my Intake Manifold being an issue?

Again, thank you for any help in this matter. If interested in that 38/38 Progressive build, let me know, I can post pics to give back to you guys, to show what I did. Because past this point, we probably don't have much in common? Unless you want to know how to build a 4.6L I6 stroker or do a lift? Lol. I mean, I'm game to see a "Monster Opel GT" if you guys are....
 

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Discussion Starter · #5 ·
Any time you’re feeding a common plenum, the ‘1.25 rule’ doesn’t apply.

That rule is based on one throttle plate per cylinder, no common plenum (Individual runners).
And that's why I came here, lol. I didn't think lf that until you said it, then it dinged in my head. I suppose the rule probably doesn't apply because a plenum adds too many variables?

When you bored out your Venturis, did you notice a loss in response in the lower RPM's? But a gain in the higher? It makes sense, to me atleast, that this would be the case, but I wonder, with a 4.2L, how it would react.

Thanks for the advice, though. I'm still kinda learning this stuff, and I sometimes over think things, lol.
 

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Discussion Starter · #6 ·
Also KEEP NOTES on everything you do so you have a clear pattern of which direction your tuning is going. Even a float adjustment can change everything. I personally HATE carb tuning. I would rather have hemorrhoids and sit on a fire ant hill.
For sure!! I did about 4 runs each in different configuration, and then I started to lose track when looking at the graphs, lol. I have since been VERY diligent on keeping notes.

For the time being, I'm using the Air Correctors and Fuel Jets. I see the Emulsion tubes, I know what they do, but I'm not sure I wanna dive into that just yet. I've got it fairly dialed in, now that I'm back home. Did another run with the 150 Fuel Jet and 200 Air Corrector. Oddly, less spikes in the Lean Dept. But I also changed my Idle jets, I was right on the cusp of 55 and 50. I think the idle jets calmed down the spiking.
I like like tuning, but it's one of those things, you can obsess about it, until it isn't fun anymore, lol. I long range shoot, too, and same thing, gotta know when to walk away, lol.
 

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Discussion Starter · #11 ·
I'm not a Weber guru, at all. I've done more research on the DGV carb than I have experience tuning them. So, I'm not going to have Rally Bob's vast experience with these carbs but I did have a couple things come to my mind.

1. Your RPM range is very low compared to most vehicles I've heard of running the DGV carb. Just look at the chart that was posted, 3500 RPM isn't even a consideration. The DGV carb is in transition till what, 2000 RPM? What I'm trying to get at, is this: a DGV tuned for your application is going to have to take this into account. We're talking diesel RPMs here. Again, I'm not a Weber guru but this jumped out at me as a significant tuning factor to take into account. I can’t imagine that a carb built to run an engine at 6000 RPM would have the same needs as a carb built to run an engine up to 3500 RPM. Your engine will spend a lot more time at low RPMs and be more sensitive to transition issues as a result I’m thinking, especially if the engine revs rather slowly.

2. The often recommended F66 emulsion tubes, might not be the right emulsion tubes for your application in case this is something that has crossed your mind. You'll need to do a lot of trial and error to tune this carb for your engine. Getting the emulsion tube right could be difficult. Never change multiple things at the same time by the way. Only change one thing at a time and see what impact it had.

What does your intake look like? Even at 3500 RPM, I would think the 38 DGAS is too small for a 4.6L inline 6.
The intake looks like this.
I'm not a Weber guru, at all. I've done more research on the DGV carb than I have experience tuning them. So, I'm not going to have Rally Bob's vast experience with these carbs but I did have a couple things come to my mind.

1. Your RPM range is very low compared to most vehicles I've heard of running the DGV carb. Just look at the chart that was posted, 3500 RPM isn't even a consideration. The DGV carb is in transition till what, 2000 RPM? What I'm trying to get at, is this: a DGV tuned for your application is going to have to take this into account. We're talking diesel RPMs here. Again, I'm not a Weber guru but this jumped out at me as a significant tuning factor to take into account. I can’t imagine that a carb built to run an engine at 6000 RPM would have the same needs as a carb built to run an engine up to 3500 RPM. Your engine will spend a lot more time at low RPMs and be more sensitive to transition issues as a result I’m thinking, especially if the engine revs rather slowly.

2. The often recommended F66 emulsion tubes, might not be the right emulsion tubes for your application in case this is something that has crossed your mind. You'll need to do a lot of trial and error to tune this carb for your engine. Getting the emulsion tube right could be difficult. Never change multiple things at the same time by the way. Only change one thing at a time and see what impact it had.

What does your intake look like? Even at 3500 RPM, I would think the 38 DGAS is too small for a 4.6L inline 6.
Here is a pic of the intake, imagine the most uneven runners you could, and a 5 year old design/draw it, lol.
Bicycle part Auto part Nickel Gas Composite material


I have thought about running a dual carb, Clifford Performance makes one. But personally, I'm kinda stuck, as I run Dual Fuel, so swap from Gas to Propane, lots of plumbing under the hood!!
Vehicle Car Hood Motor vehicle Automotive design


But, you guys are onto something I think!!! Yeah, emulsion tubes may be out, unless I plug holes. Nobody seems to make them for keeping a rich condition for longer. Wonder why? Maybe because Webers belong in sports cars? Lol. Makes sense. But I did a quick run this morning and think I found a way to "delay" the emulsion tubes. I have F50, BTW. Redline sells this carb with a 2mm Needle Valve. I noticed a while back that in the EU, most cars in the V6 variety have a 2.5mm needle, and they're even smaller, still, 3.0L. Odd, but I thought nothing of it until now that you guys said this.

My theory? If my big 4.2 is sucking up ungodly amounts of fuel, and it is, then I'm emptying the bowl earlier, turning "on" the lean side of the emulsion tubes. I switched to a 2.5mm this morning, seemed to help, actually!! This kind of changes the Lean "curve" or "turn on" timing of it, if that makes sense.

And of course, my longer run I did with this change? I popped out my SD card without turning off Record, so most data was lost, but the shorter runs seemed promising.

If course, now I may have to go back and lower my Fuel Jet settings. As I was using those tkncreat a lean condition. Sigh, where is that ant pile? Lol
 

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Discussion Starter · #12 ·
The 38DG-series carburetors were OEM on European Ford Granadas. We’re only taking 2.5 liter and 3.0 liter engines, but they revved a bit higher than the 4.2 liter Jeep engines.

Seeing how the Jeep is all about the low rpm torque, I’d say that even the standard 330-cfm airflow rating from a 38DG-series Weber is suitable. Certainly enough for 150 hp.

Boring the venturies for higher airflow may help at 5500 rpms, but you’d lose some of the carburetor’s flexibility down low.
Ok, that's what I kind of thought, but wasn't sure. Basically, I'd get an "Overcarbed" situation, vs an "under carbed" situation. The 32/36 I had on there was INSANE!! I was romping on cars at lights, lol.

Until, 50 MPH that is..... 1st gear I think got me to about 10 MPH? but it was fun!!
 

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Discussion Starter · #13 ·
I found this older thread to be a very enjoyable read, the majority of the focus is on the idle and progression stages, closer to what you have than our little 4 cylinder engines. The first half of the very long thread is really educational, the second half towards the end it looses its focus like any typical lengthy thread.


I’d be surprised if you hadn’t read it before.
It lured me in particularly when he removed the factory air corrector jets for the idle circuit, thread tapped them and replaced them with various sized air correctors, obviously there’s a whole range of idle jets to choose from, this just adds a whole new perspective on jetting the idle circuit. Some good fine tuning discussions.

Detailed pics etc of the 38/38 that you put together I would think would be of interest if you post them up here.
Too funny, I'm a part of that Forum. I don't think Shawn is in there anymore. Yeah, that place can get off the rails quickly.

There are alot of good guys on there, taught me alot, but when it comes to Weber carbs, they seem lacking in expertise, for the most part. And I took on Webers as my personal "niche" in there.

Most guys there will tune, and then when it "feels" good, call it good. As far as I know, I'm the only one that has put an AFR to it, and logged it. It actually started when I called Redline, guy said I have a Rich condition (humidity/heat in FL) for my idle. Ok, bought the High Altitude kit, fixed idle. But something wierd happened, I was SUPER lean up top In RPM's. Like, burn your eyes lean, never touched the jets myself. Then I got into the Weber manuals, noticed the jettings of Weber 38's in Europe. This didn't match "our" (US carbs) jetting at all. I posted this in Jeepforum.com. crickets, lol. I then got an LM-2 AFR, gonna figure this out . I kinda did. They are sold Lean!!! Redline has, obviously, more expertise than me, same with Pierce Manifold, I've talked to both, neither had answers to the discrepancy of US jetting vs EU, or why a smaller V6 in Europe would have beefier jettings. I don't blame them, God knows, they aren't dumb with carbs, and CERTAINLY smarter than me. And Jeep guys don't tend to push. I have a feeling, just gut, that our 38/38 kits are sold "for Jeeps" with minimal truck tuning, if any. It is probably the same carb they sell to the VW guys, lol.

I am also going to Dyno it. Again, Jeep guys..... sigh.... they will spend thousands of dollars on 4.0L head on a 4.2L block, get cams, spend thousands of dollars. And know what they say? "It feels better....." or, "yeah, definitely stronger!!", and that's it. Probably 30% of Jeep 258's have the 4.0L head mod, and not a single Dyno or even a 0-60. Nobo6can even PROVE if it's the 4.0 head or the F.I. mod that gains the supposedly 4p HP. Other guys will spend thousands and say, "I gained nothing..." lol. And they will have 2 weeks debates about "what they felt". In terms of exact performance? In the Jeep world? It's archaic. I'm trying to maybe put an end to it. Or atleast, "show for my work". If that makes sense.

You guys have time slips, 0-60, 1/8 miles, track runs, etc. Jeep guys got, "Feels better" and "I know I'm right". I'm trying to blend the worlds. For $150 Dyno run? To prove or disprove what hundreds of guys spend thousands on? IMHO, that's a decent deal, they know it, too, some are excited to see Dyno results.

I love my fellow Jeepers, but sometimes they drive me bananas, lol.
 

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Discussion Starter · #16 ·
Ok, the dual fuel bit… that is interesting. Are you running them both at the same time or only one at a time? How is the propane system working?

It’s still worth trying the F66 emulsion tubes. They are the go-to emulsion tubes for our engines, it’s possible they are the right ones to help out with a lean condition. I could be wrong, but my memory is telling me that if someone was running F50’s and struggling with a stumble at lower RPMs, the F66 tubes fixed it. Rally Bob would know more about why the F66 tubes are recommended.
The duel
Ok, the dual fuel bit… that is interesting. Are you running them both at the same time or only one at a time? How is the propane system working?

It’s still worth trying the F66 emulsion tubes. They are the go-to emulsion tubes for our engines, it’s possible they are the right ones to help out with a lean condition. I could be wrong, but my memory is telling me that if someone was running F50’s and struggling with a stumble at lower RPMs, the F66 tubes fixed it. Rally Bob would know more about why the F66 tubes are recommended.
The Dual Fuel is an either/or set up. Very few Jeep guys run both, in fact, mine is actually made for a Toyota 4 Runner. It's actually pretty amazing. It acts like Fuel Injection, as it's actually a pressurized gas, so instant into the engine. And lots of offroad guys use it instead of fuel. If you tip, it wont spill gas, if you are upside down, it wont stop-pressurized vapor. I don't use it for that, lol. I got it because I live in FL, and when hurricanes come, I can run a vehicle off of BBQ tanks. I also have a larger forklift tank I can put in the back.

I'm gonna buy some Emulsion tubes. I had some spares, and soldered some holes shut. Unfortunately, I didn't do the right ones!!! When they say "high RPM", I questioned myself, high RPM for them? Or for me? At 3,500? Welp, I got it wrong, lol. But.... learned something in the process!!! Here is the emulsion test tubes.
Wood Tool Household hardware Cosmetics Gun accessory


Here is the AFR log from before this mod'ed tube.
Rectangle Slope Purple Line Plot


11.26-14. The spikes are where I release the gas/shift. My AFR is only about 18" from my rear exhaust, so this happens, I've read.

Now, with my wrongly filled tubes, lol.
Purple Rectangle Font Handwriting Magenta


11.10-18, so, clearly, emulsion tubes do change things!! You just have to do them correctly, lol. Live and learn....
 

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Discussion Starter · #17 ·
At what point do you just jump to the Holley 2bbl? Not the DFAV, but the Holley replacement for the Motorcraft 2bbl.
I wouldn't disagree with that, lol. Because I have a Weber, a few of them. It's kind of like battery powered tools, why do I have Makita drills? Because they have some of the best battery powered saws on the market, lol.

But you do bring up a good point, I see where people talk about the Weber 38 flowing the same amount as the Holley, 390 CFM? But then some bring up the 3 inch vs 1.5 inch measure, in water? Or something? Again, truck/jeep guys not dynoing their stuff. So it makes it even harder in this hobby to decide!! There is no thread on a forum saying, "I ran 0-60 with this carb", and someone answering with, "I'm stock, too, but with this carb I ran...."

It is ALL guess work. I'm trying to change that, to be honest. Even after this carb and dyno, gonna dyno it with some other engine mods, just for records, so to speak. It also doesn't help that Jeeps vary so much. An example of a "Jeep thread", new fellow posts, "Hi, what carn should I get? The Carter BBD sucks. I just want some more power. You will see 4 answers: 1: get a V8 or 4.6 Stroker. 2: Get a Motorcraft 3: Fuel Injection & 4.0 head from junk yard. 4: Get a Weber (and this could be 32/36 or 38/38), and even more answers. What the new guy isn't aware of, is that V8 dude just wants to romp on cars at stop lights, the Motorcraft guy wants to spend no more than $200, the 4.0 guy wants to go 4x4ing and a family vehicle, the Weber guy is city driving and MPG conscious, the 4.6 Stroker guy wants to climb over trees and rocks by just letting the clutch out in 1st and climbing stuff. And they all wanna talk about how 1 is better than the other, without seeing their differences, lol. Too many options!! I'm trying to document, and see what does what, so to speak. Because to top off all those guys' builds, almost none of them have the final power numbers. So, I'm trying to be different, lol. It costs, but so be it, I'm learning.

And yeah, I know, the minute I change something, I'm gonna have to go through this all again, lol.
 
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