Weber Set-Up and Tune Discussion - Page 3 - JeepForum.com

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post #31 of 1100 Old 08-08-2010, 08:17 PM
John Strenk
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Part 2.

Butterfly valve idle position. I set the bottom of the butterflies flat with the bottom of the first progression hole and use threadlocker to fix it so I will not move it by accident or desperation, for the people who have work on DCOEs or IDA/IDFs it will be familiar, the 50 or so RPMs available with the 1/8th of a turn limit either way does not make much of a difference but it could easily mess up in the tuning of the Idle-progression circuit. Now, this is my method and I know there are other methods from people that are more qualified than myself and in no way or form I'm saying that this "is" the holy method, it is what has worked for me after hitting the wall so many times.

Reasons. When the butterfly is set at this point the three progression holes since they are connected to the idle-progression duct and don't have check valves they let air go into it leaning the mixture reaching the idle port, they together with the calibrated bushing work as an air corrector jet/emulsion tube of sorts for the idle-progression circuit. When the butterfly starts to open this first progression hole is exposed to vacuum from the manifold so now instead of letting air in it lets mixture out to keep the air fuel ratio within range, but also since it is no longer supplying air to the mixture going to the idle port this mixture is also richer which is good since the flow from this port has been reduced from the lower vacuum available, so in other words, holes above the butterfly let air in and below the butterfly let mixture out, the process is the same when each of the progression holes becomes exposed to the vacuum below the butterfly, enriching the mixture furthermore since the volume of it does not increase linearly due to the ever lower vacuum acting on them.

At idle, if the butterfly is below the first progression hole and the idle mixture screw is set properly, as soon as you start to open it more air will rush in but no increase in mixture will be available even worse since the flow from the idle port will be reduced due to lower vacuum sending the air-fuel ratio to the roof and a lean spot will appear until it reaches the first progression hole. When the butterfly is above the first progression hole at idle the response of the idle mixture screw will be little to non existent depending on how high it is the butterfly, but things don't end there, since you have two ports flowing mixture into the manifold and an enriched mixture to boot, it will mimic a "too big idle jet", and then when you correct it you just have leaned whatever is left of progression letting you believe that the main circuit needs to come earlier than actually needed
If after the carburettor and the timing are spot on you find yourself in need of more idle speed because of the alternator or power steering, etc. you can drill a 1mm. hole in the butterfly and if still not enough you can keep on increasing the hole 0.5mm at a time until you reach the point you want.
Sorry it has been this long but the devil is in the details. I hope I have covered all the bases.
Jorge.
I had to read this several times. I don't think it's all that sensitive, Heck, when my carb bowl runs dry, I can pour a shot glass of fuel down the carb and the engine will idle just fine until the fuel pump fills up the fuel bowl again.

One thing to remember is that the idle mixture control screw is more of a flow control than a mixture setting. the air/fuel mixture is set with the jets ports before the idle screw so there is plenty of pre-mixed fuel available for the transfer port. THe mixture in the well well does get richer as the throttle passes the transfer ports but more air is going into the engine also. There also is the accelerator pump that helps the mixture at the times between the main circuit starts to work.

I think that the vacuum level is quite high anytime the throttle plat is near the transfer ports. not quite like you describe it. Even though the manifold vacuum may be reduced a little the air rushing pass the transfer port creates a vacuum on it own that is quite high forcing more mixture out the port so there is no lean point to worry about.

You also have to consider the manifold design. a long manifold on an I6 acts like a plenum chamber that the cylinders can draw off as needed so the mixture control is not as isensitive as on an DCOE delivering fuel to each individual cylinder. We're still talking tractor engines here not a 900cc Fiat Abarth engine.

The hole drilling is a good idea, even my BBD off a V8 has holes in the throttle plate. One thing you have to remember though is that with the hole in the plate you need a richer mixture available in the well but still have the idle mixture control screw in the right position. Other wise if the mixture control flow screw is out to far, flowing a lot more mixture, the not enough mixture will be available for the transfer ports. and a nice little off idle bog. So your hole size should be just enough to get your RPM up to the right speed when the throttle is closed at least below the 1st transfer port, AND the idle mixture control valve is in the correct position.

You will see many people mentioning the correct number of turns the mixture control screw need to be set at.

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post #32 of 1100 Old 08-20-2010, 01:19 PM
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Originally Posted by outsider2010 View Post
Part 2.
If after the carburettor and the timing are spot on you find yourself in need of more idle speed because of the alternator or power steering, etc. you can drill a 1mm. hole in the butterfly and if still not enough you can keep on increasing the hole 0.5mm at a time until you reach the point you want.
Sorry it has been this long but the devil is in the details. I hope I have covered all the bases.
Jorge.
This was a tuff read... But I think I got it...
As long as the throttle plate is below the progression holes, and there is ZERO vacuum at the "S" port or ported vacuum for advance.
You drill a 1.00mm hole "WHERE" in the throttle plate to increase air volume which will increse your idle speed.
You know, once you do this, fixing the throttle plate is slim to non-existant. Even if you get a new throttle plate, it never recenters like the original Weber installation. (?) A better solution would be a 38-DGES, which is at least the same size as the Carter BBD that you took off the engine in the first place.
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Last edited by uptillnow; 08-20-2010 at 01:49 PM.
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post #33 of 1100 Old 08-20-2010, 01:28 PM
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Originally Posted by John Strenk View Post
One thing to remember is that the idle mixture control screw is more of a flow control than a mixture setting. the air/fuel mixture is set with the jets ports before the idle screw so there is plenty of pre-mixed fuel available for the transfer port. THe mixture in the well well does get richer as the throttle passes the transfer ports but more air is going into the engine also. There also is the accelerator pump that helps the mixture at the times between the main circuit starts to work.
I agree, this is how I understand the "mixture" screw. It is a VOLUME screw and mixes nothing. The mixing is done "in" the idle jet using a non replacable air jet at the parting surface of the fuel bowl. This already emulsified mixture is then controled by increasing or decreasing this volume by turning the "volume" / mixture screw.
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Last edited by uptillnow; 08-20-2010 at 04:56 PM.
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post #34 of 1100 Old 10-08-2010, 02:26 PM
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When I had to drill the hole in the plate I did it in front of the progression holes at 5mm. from the edge, and never drilles to more than 2mm. Althought ther is a better way but not as kosher and it is to use avacuum inlet at the base of the carburetor in the manifold and attatch a hose and a small valve and open it until you get the idle were you want it and connect the other side of the valve to the clean side of the air filter.
Jorge.
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post #35 of 1100 Old 10-08-2010, 02:31 PM
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Regarding the idle mixture needle I agree that it is just a flow valve but what I ment is that the mixture gets further diluted after the air bushing by the progression holes exposed to atmospheric pressure (above throttle plate) since there is vacuum in the passage, but as you lift the plate, the situation changes for the next hole to be exposed to vacuum and now instead of letting air in leaning the mixture let mixture out and so on and so on.
Jorge.
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post #36 of 1100 Old 10-08-2010, 02:40 PM
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It si true that a better solution would be a 38DGES and a better one a 40DFAV and the best a 48IDF, but people keep on buying the 32/36 and installing them making it harder on themself that is why I posted in other thread that it shouldn't be sold as a kit for anything beyond 3L. since the new owner will learn to hate the carb because it is so hard to set properly and will conclude that Webers are not worth it or even good.
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post #37 of 1100 Old 10-08-2010, 02:42 PM
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The 32/36 is tunable to bigger engines but takes a lot of time and sensitivity, it is more like a challenge than a bolt on replacement.
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post #38 of 1100 Old 10-08-2010, 03:47 PM
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Swatson Good thread. Thanks For all your help with My 32/36.
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post #39 of 1100 Old 10-08-2010, 04:19 PM
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Originally Posted by ozzieb View Post
Swatson Good thread. Thanks For all your help with My 32/36.
How did your carb work out? What happened? This was a long time ago you had some linkage problems, then a starting or quiting problem? What happened?
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post #40 of 1100 Old 10-08-2010, 04:28 PM
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So I should ditch the 32/36 in favor of a bigger Weber? I am just asking, I have the 32/36 and it seems to have hesitation when I gas it. However I will add I have not done anything to the carb. to try and adjust other than, add a regulator. I do like the plug and play option if there is one.
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post #41 of 1100 Old 10-08-2010, 04:38 PM
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So I should ditch the 32/36 in favor of a bigger Weber? I am just asking, I have the 32/36 and it seems to have hesitation when I gas it. However I will add I have not done anything to the carb. to try and adjust other than, add a regulator. I do like the plug and play option if there is one.
The 38-DGES is the same size as the Carter BBD that you took off the Jeep in the first place. The 32/36 DGEV runs on one barrel 32mm untill half throttle when the 36mm barrel starts to open. The 32mm barrel is 1/3 the size of the original carb and the 38-DGES.
Now, with that said the 32/36 can be made to operate a 258 Jeep. The jetting that seems to work for all around performance is a .75mm Primary idle jet and a .60mm secondary idle jet. Ussually both main jets are 1.45mm and a primary air jet of 1.70mm and the secondary air jet at 1.60mm.
Then, the trick is to have the engine idle at zero vacuum at the "S" port or spark port and the idle speed screw absolutley no more than 1 1/2 turns in. Then the timing is set to 8-10 BTDC, some go more and some go less. The idea is to have an idle speed and no pre-ignition. What are your settings on your carburetor? Do you know what your jetting is?
I love my 38-DGES. It is the same size as the Carter BBD and works GREAT!
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post #42 of 1100 Old 10-08-2010, 06:16 PM
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Originally Posted by uptillnow View Post
The 38-DGES is the same size as the Carter BBD that you took off the Jeep in the first place. The 32/36 DGEV runs on one barrel 32mm untill half throttle when the 36mm barrel starts to open. The 32mm barrel is 1/3 the size of the original carb and the 38-DGES.
Now, with that said the 32/36 can be made to operate a 258 Jeep. The jetting that seems to work for all around performance is a .75mm Primary idle jet and a .60mm secondary idle jet. Ussually both main jets are 1.45mm and a primary air jet of 1.70mm and the secondary air jet at 1.60mm.
Then, the trick is to have the engine idle at zero vacuum at the "S" port or spark port and the idle speed screw absolutley no more than 1 1/2 turns in. Then the timing is set to 8-10 BTDC, some go more and some go less. The idea is to have an idle speed and no pre-ignition. What are your settings on your carburetor? Do you know what your jetting is?
I love my 38-DGES. It is the same size as the Carter BBD and works GREAT!
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I'm not gonna lie I have no idea what the set up is. The carb is all original I have not adjusted anything other than PO set idle and such.
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post #43 of 1100 Old 10-08-2010, 06:45 PM
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i have a question. i have a weber 32. its running so rich. black smoke come outs when you start it and a small mixture of water and oil. the engine is very strong.i just had the valve cover gasket replaced and it had some sludge on the valves.i'm using rotella and wix filters and have changed it twice and the oil is still dirty looking after driving 300 miles.now the past week after driving the car for a few miles and coasting at low speeds the car will cut off for a second and start right back up and not due it again. its happened 3 times in a week.any help on what i need to do appreciated
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post #44 of 1100 Old 10-09-2010, 09:31 AM
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rclark678:
If you want "plug and play" the 38DGES is your carb, the 40DFAV would be better but is hard to find in good shape since it hasn't been made in over 20 years plus parts are there but are not plentiful.
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post #45 of 1100 Old 10-09-2010, 09:35 AM
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cj7jeep:
Check your choke, it should be fully open when engine is warm, then check with engine running at idle that no fuel is comming from aux. jet, if it does the float level is too high or the valve is defective and last the power valve diaphragm could be ruptured keeping the valve open all the time simulating a very big main jet. Good luck!
Jorge.
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