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Unread 10-30-2010, 04:20 PM   #76
swatson454
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Quote:
Originally Posted by uptillnow View Post
This is a very interesting and advanced experiment here. I have heard of drilling out the air bleed for usage at or above 6000 feet elevation. I believe the 38-DGES has a 1.90mm air hole and drilled to 2.00mm or 2.05mm helps allot for the Jeeps drivability at altitude. What material did you use and how did you thread the air bleed? Also, I know by reducing the size of the air bleed you would be able to use a smaller fuel jet keeping the “reasonably” same atomization and drivability and reduce the volume of fuel blowing out the exhaust. What sizes air bleed with what size fuel jet have you tried? What are your driving air fuel ratios, if you have them?
Shawn, thank you for sharing your information, I could see how you could easily ruin a perfectly good carburetor by not being careful.
UPTILLNOW
It requires a 10/32 tap and the appropriate bit. I'm having a hard time finding the allen-headed, brass plugs but you can purchase a kit from Paul at www.performanceoriented.com. Mcmud found him several months ago and it turns out that he and I have a very similar approach to carburetors. He's a really cool guy and can put a kit together for you.

You're right, the 38 is supplied with 1.90mm air bleeds and I've been around the world with them. I've gone from 1.50 up to 1.90 in .5mm increments using a pair of 45 idle jets and I do like the way they're a little leaner on entry than the 50s and quite a bit better than anything larger than that.

With 1.2mm holes in the throttle plates, the 45/1.70 was perfect. The rich entry was leaned quite a bit with the holes without adversely affecting the entire progression. The idle just wasn't quite stable enough for me. I'm convinced that an engine with a performance cam, heads, intake etc would respond extremely well to that modification. It just wasn't quite right for a stocker so the holes were soldered up.

Personally, I liked the 45/1.80 or 1.85 combo with the F50 emulsion tube. It wasn't as rich on entry as the 50/1.90 combo, which would come in around 13:1 under the lightest of input, but held on to a decent mixture a little longer than a 45/1.90 set up.

I'm currently using a 45/1.90 which seems to tip in in the higher 14s afr but I've also been playing with the emulsion tubes. Here's a shot of an F50, which is installed from Weber, an F6 and an F7 on the right.


The pattern of large holes placed higher up on the tube of the F50 makes for a lean entry and then a large amount of air is let in once activated. The F6, center, is better but tips in quite early, followed by excessive leaning on fairly large throttle opening, and then a really powerful midrange. The F7 was even richer on entry but equally powerful.

Here's my modified F7, which, after six hours of modifying and testing, we can refer to as an F-THIS

The upper holes with a 3/4 inch float drop seem to bleed off enough well depression at light throttle to allow a nice cruise on the progression circuit. When the throttle is opened quickly, the middle pattern is much more responsive than the F50 and seems to deliver a very strong mid-range punch, where the F50s always went lean, and the lower hole pattern seems to be holding the wide open throttle afr linear at about 12.6:1 up to redline using a 145 main jet, 175 air corrector combo.

I'm afraid I'm at the limits of testing accuracy with this tired old engine and without a controlled environment but this has quite a bit more mid (1,800 rpm) and upper-range power and response than the F50 and needs less jet to do it. The lean hole at large throttle opening experienced with the F50 is gone now and the mixture is more consistant. So far, so good...

Side note: I'm sure my piss-poor gears have exaggerated any lean entry that the F50 emulsion tubes may have had. A decent gear set or an automatic would likely rpm right over any leanness and you'd probably never know it was there.


Shawn

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Unread 10-31-2010, 02:48 PM   #77
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Based on previous experiences and this most recent work, I'm going to offer up some broad generalizations while it's still fresh in my mind and wait for your feedback.

The activation point and also the mixture strength of the main circuit is controlled by the emulsion tube to a much greater extent than the main jet or air corrector. It also is the key to how well the main circuit responds to large throttle openings and overall mixture consistency, once activated.

The true mixture strength or sizing of the main jet is measured down lower in the rpm range (2,500 rpm) at WOT and is influenced to a lesser extent by the lower holes of the emulsion tube.

The WOT mixture at the top of the rpm range is most influenced by and adjusted with the air corrector.

Thoughts?


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Unread 11-01-2010, 01:48 PM   #78
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Quote:
Originally Posted by swatson454 View Post
Here's my modified F7, which, after six hours of modifying and testing, we can refer to as an F-THIS


Shawn
Shawn,
Thank you for your results from testing the idle air bleed sizes vs. idle fuel jet sizes within reasonable air/fuel ratios and reasonable sensing the power results. I like your results from the idle circuit to main circuit tip-in while changing to the F6 emulsion tube, this opens up an advanced tuning and new look in power vs. fuel usage. I have used the jetting that typically comes in the 38-DGES and adjusted (lowered) the float level (18mm) to delay the main circuit entry which also helped eliminate that transitional “excess” of fuel at the end of the idle circuit entering into the main circuit. 3/4" or .19mm seems like it is too low for a float level, I will try this also. The accelerator pump nozzle is also used as a “High Speed” enrichening device. I believe the 38-DGES comes with a .70mm accelerator pump nozzle size, by decreasing that size without sacrificing the needed fuel from the pump shot should also decrease that transitional air fuel ratio a little more. I am out on that F7 E-tube now called F-THIS.
So I am going to try this F6 e-tube and lowering and raising the float level for timing the main circuit entry. This is good stuff…. Thank you again for sharing this.
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Unread 11-01-2010, 02:12 PM   #79
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So I am going to try this F6 e-tube and lowering and raising the float level for timing the main circuit entry. This is good stuff…. Thank you again for sharing this.
UPTILLNOW
Yeah, I'd love to be able to tweak things and compare notes. Very cool!


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Unread 11-02-2010, 03:01 AM   #80
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Since emulsion tubes hole and fuel levels are closely inter-related, Have you tried the engine at different angles one might find offroading? I confess that most of my Weber experiments have been done on flat surfaces at high Gee's but not starting from idle on the side of a hill. I remember it was easy to flood an engine in a high Gee turn with a Weber if the floats were mounted 90* from the way the carb was designed to work. It was always better to get the right manifold so the carb was mounted properly rather than adapting the carb to work with an OEM manifold if it meant mounting the carb wrong. I really like the Clifford manifolds that accept a number of different carbs.

You can't see the difference between those three emulsion tubes but some had various diameters also that would also effect the mixture. I remember chucking some e-tubes into an electric drill and reducing the diameters down to change the mixture.

You can see there are so many variables here a guy could go crazy modifying the carb to fit their engine.

One nice thing is that if you understand how a carb works, I mean really works, then this knowledge is also perfect if you ever go to FI and have to adjust the fuel tables. Every thing Shawn talks about how modifying the Weber to make his engine work would be invaluable if he ever went to FI. All the time you read about some FI conversion not working properly and looking for a new program or prom to get his engine to work right. So even though we are talking Webers here, this will apply to any fuel delivery unit you will ever work on.

One other thing I'd like to mention since this is a discussion on Webers is that what works on one 2 bbl manifold/exhaust setup might not work on a 79 or earlier manifold exhaust. You're going to have to learn how the carb works and what to look for to make your Weber work with your engine. Also consistency is important to testing as well as one change at a time. I had a hill that was a constant grade for about 1.5 miles that was a great chassis dyno. You could run your engine at a certain RPM to check performance on various modification.

Maybe we need a "how to check and verify changes" without access to a dyno at the end of this discussion. Plug cuts, stopwatches and mixture meters are all great to measure, I've even used a Gee meter when I had nothing else. (That's G as in gravity not G as in "Gee it works great. )
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Unread 11-02-2010, 03:06 AM   #81
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DDoouubbllee PPoosstt. I hate 5:00

Last edited by John Strenk; 11-02-2010 at 03:08 AM.. Reason: Double post
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Unread 11-02-2010, 10:30 AM   #82
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Quote:
Originally Posted by John Strenk View Post
Maybe we need a "how to check and verify changes" without access to a dyno at the end of this discussion. Plug cuts, stopwatches and mixture meters are all great to measure, I've even used a Gee meter when I had nothing else. (That's G as in gravity not G as in "Gee it works great. )
Thanks John!

There have been quite a few times when I wanted to run up the road behind the house here and do a plug cut at various air/fuel ratios and post up pics of the spark plugs. Then the thought of being on the side of the road with the hood up and a handful of hot spark plugs wins out over the idea of good information

Maybe I should just hike up my skirt and do it. The plugs are only two weeks old so we'll see...


Shawn
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Unread 11-02-2010, 12:17 PM   #83
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Thanks John and Shawn,
The ideas surrounding "how to check and verify changes" would be a very good topic, and if I don’t remember, please anyone/everyone step up and kick around some general ideas. Without having an accurate way to measure power, torque, speed etc I have resorted to using the "bracketing" methodology, add fuel till it gets worse and then back down, add air till it gets worse and back down. All of this is my “seat of the pants” analysis.
The emulsion tube changes have, for me, have always been the “Black Magic” with regards to fuel curves, fuel volume, and RPM that works for my/the application. Fine tuning dual DCOE’s on a dyno has been my experience. I like the E-tube on a drill and changing the outside diameter slightly, and having it make significant changes. The “F-This” emulsion tube is a similar type of experimenting that didn’t go in the right direction and allowed Shawn to successfully change his direction to the F6 E-tube. These sizes, the I.D. of the emulsion tube the O.D. of the tube AND the consistent position and size of the hole in the carburetor all transfer the volume of emulsified air and fuel. Again as stated earlier the float height, or, fuel height submerging the emulsion tube also becomes an important consideration in tuning at this level we are speaking about.
But back to reality here, we are still speaking of an old technology tractor engine in a Jeep that typically spins out to about 5500 RPM and develops it’s peak torque around 1200 RPM. Driving as a rock crawler, from off idle low RPM torque and power to mid range (2500 RPM) is where this “tractor” engine shines…
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Unread 11-02-2010, 01:48 PM   #84
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The “F-This” emulsion tube is a similar type of experimenting that didn’t go in the right direction and allowed Shawn to successfully change his direction to the F6 E-tube.
I chose the F7 because three days of taking notes with the three different tubes had me convinced that the F7 would require less work to get what I was shooting for. I named it the "F-This" because I nearly burned one finger while soldering and sunk a 1mm bit in another finger during the course of the day. Getting a 1mm hole collared on a tight radius is no picnic and I'm stuck with basically nothing that even remotely resembles a decent shop area.

On a serious note, I'm quite pleased with how the tube mods went and the final result. I took it slow and only made one change at a time after carefully considering what the desired result should require.

I started at the top and focused on getting the amount of initial well bleed-off that I wanted at a certain rpm and throttle.


I then moved to the middle of the tube for the weak throttle opening that I initially wanted to tackle. The lower position of holes on the F7 compared to the F6 is why I chose it as the base to work with. It was a step in the right direction compared to the F6 and F50 but I still felt that I could get some quicker response time out of it and richen the mixture up a bit so I began soldering up specific holes and testing.


I didn't take a pic of every change but that was the basic idea. I made really small changes at a time which ended up allowing me to sometimes move back up to the top of the tube or vice versa and finally landed here.


I didn't mean to make it sound like I went in there and screwed up an emulsion tube and had to go back to an F6, I tend to write like I talk with friends; which can be fun, goofy and sometimes hard to read. I'm extremely pleased at how this went but I'd be a liar if I said that I didn't enjoy having an F6 backup in case I really screwed the pooch.


Shawn
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Unread 11-02-2010, 03:58 PM   #85
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Quick question guys; I like your idea of trying to document different testing methods, especially plug reading. I'm on the fence as to its accuracy unless you've got David Vizard's or John Kaase's expertise so it could be a real learning opportunity for me and I'm sure others as well. The question is, should we tackle it here or start a new thread?

John, being in Las Vegas and probably not the worlds best rock crawler, all of my testing has been on level ground. If I ever pull any g's worthy of note, I'm in a world of trouble and not looking at the a/f monitor!

Uptillnow, I agree with you completely with midrange power being the ticket with these things. Was spark plug reading part of your jet selection process along with bracketing?


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Unread 11-02-2010, 04:14 PM   #86
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Uptillnow, I agree with you completely with midrange power being the ticket with these things. Was spark plug reading part of your jet selection process along with bracketing?
Shawn
NOPE.... While I went to A & P school and wound up being a mechanic, I just learned about lead (aircraft fuel) on plugs, I don't have a magnifing glass to look at where the ceramic meets the steel and "read" the plug in that area, I am like you to the extent that "actually" reading plugs is an educated art form. Not just "it's black and sooty" It must be rich. A lean foul on a plug will also look like it is too rich. Within the bracketing I can go to the "too" rich to the "too" lean and then know the range within that engine. This is the extent and range that I use and call bracketing.
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Unread 11-02-2010, 04:40 PM   #87
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John, being in Las Vegas and probably not the worlds best rock crawler, all of my testing has been on level ground. If I ever pull any g's worthy of note, I'm in a world of trouble and not looking at the a/f monitor!
Shawn
Shawn, I know I am preaching to the choir here, the 38-DGES does not slosh fuel over like the 32/36 DGEV. The 32/36 DGEV can be modified to block off the fuel slosh over from the fuel bowl to the throats. The 38-DGES is probably the BEST choice for even a 1300cc Samurai just for the mounting trouble they have and stalling out due to fuel slosh over when using the 32/36 DGEV. As far as the Jeep rock crawling with the 38-DGES... Well, it's still a carburetor not fuel injection. The 38-DGES out performs (I would say) all other carbs when lowering the float level to 18mm maybe 19mm. This would help the fuel "level" submerging the E-Tubes and still have that extremely good low RPM torque and control that is needed when crawling rocks at angles that would scare Evel Kneivel.
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Unread 11-03-2010, 02:41 AM   #88
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Plug cut got old fast and hard to do properly. The best was a stop watch and performing 10mph to 30 mph or 20mph to 60mph timed runs. These you can do all day under various conditions. I use to do them on the way to work each morning at various location. And easily repeated. I think you can even calculate the HP from that data if you know the weight of the vehical.

When I set up my Suzuki Samurai (32/36 DGEV?) I used the O2 sensor and cheap data logger. I think the data logger had 4 inputs so I could monitor the A/F ratio, RPM and throttle position. I got that carb so dialed in that when I went for e-check on the rollers, they recalibrate their equipment just to make sure the results they were seeing were real. Before I put on the Weber I always failed and had to go to a certified repair shop and spend my $300 before I got a waiver. Stock the Suzuki was horrible with emissions but after putting in a Isky cam, headers and Weber, it out preformed my FI car on the rollers.
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Unread 11-03-2010, 05:25 PM   #89
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When I set up my Suzuki Samurai (32/36 DGEV?) I used the O2 sensor and cheap data logger. I think the data logger had 4 inputs so I could monitor the A/F ratio, RPM and throttle position. I
Hey John, Who's "cheap" data logger did you use? I have googled them and found a huge range that won't suit my needs. I think a 4 input is plenty. Did you use a wide band O2 sensor and display?
Also, I see you have a Samurai, Yeeaaa... Do you have any trouble with "fuel slosh over" using your 32/36 DGEV?
Thanks for your input, I always re-read what you have to say.
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Unread 11-04-2010, 02:52 AM   #90
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I used a Gulton Rustrack Ranger data logger. It said it was for power data logging but the inputs were simple millivolt inputs. I've seen them go for as little as $50.00 used on ebay.

I wish I had a wideband detector but those cost more than the data logger back then. I just ended up exporting the data into excel and looked at the average voltage for my test run to see if the mixture was correct.

I bought it to hooked up some simple government issued accelerometers back in my racing days.

When I got married and my family started growing I had to trade in the Sammi for a van. But eventually I traded the Van for a Jeep. . I don't recall any issues with fuel sloshing but I did heavily modified the Weber. I even put in an electronic mixture control off some other production weber from some other vehical.
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