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Unread 06-14-2010, 03:28 PM   #1
swatson454
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Weber Set-Up and Tune Discussion

I thought we might get a thread going where we could all share and maybe cover some of the basics and what appear to be the most common challenges that we face when installing a Weber and hopefully get some good discussion going.

This thread will begin with a more focused view on the initial set up, the importance of the base-line settings and general discussion of a Redline Weber carburetor and not really intended to be a troubleshooting guide. It’s rather an offering to a trouble free installation and use thread.


Size Selection

Set up correctly, either the 32/36 DGV or the 38 DGS should provide great performance and mileage on the 4.2 or even the 2.5. I’ve just been tickled pink with my 38 and I know others who love their 32/36 DGV.

Here’s a good link, should you still be deciding which carb will work best for your application.

Making The Right Choice 32 or 36


Adaptor Plates:

The adaptor plates need a close inspection and possibly attention prior to assembly to avoid problems with vacuum leaks. They are often delivered with uneven mating surfaces, casting flash and just about any number of abnormalities that you can think of.

It is well worth your time to give them a close inspection before the install. By using a straight edge over the entire mating surface of each side of the adaptor plates, you’ll be able to tell if the surface is flat. They sometimes need some sort of work in this area and some filing and sanding may be needed to ensure a flat surface. Should the plate need some work to flatten out, you can place a sheet of wet/dry sandpaper on a flat surface, oil it and sand away any high spots.

Once the adaptor plates have a good, flat surface to work with, you can go ahead with the assembly of the plates. It’s a good idea to lightly coat some wheel bearing grease over both sides of the mounting gaskets to ensure a good seal. You may want to perform a test assembly to make sure the mounting bolts are long enough. I’ve seen kits that actually required a trip to the fastener store for bolts that were a touch longer than the ones supplied.

Once the plates are secured to the manifold, you can thread the carb studs into the top plate. This is a part of the initial assembly where some mistakes can be made. If the studs are actually tightened down, they will serve to pry the adaptor plates apart and cause an air leak. Rather than tightening the studs down, simply coat the threads with red Loc-Tite, screw them down until they just make contact with the lower plate, back them out 1/8th turn and walk away until the Loc-Tite has set.

A little Teflon tape on the threads of the PCV port and you should be good to go with the adaptor plate assembly.


Curb Idle Throttle Plate Position

Here’s where the vast majority of complaints and confusions arise when it comes to setting up a Weber.

When installing either of the Redline Weber conversions, I suggest the first thing you do is to flip the carb upside down and determine the maximum amount that the throttle plate can be opened for a proper curb idle throttle plate position.

To do this, you’ll need to use your fingers or maybe insert a short piece of 3/8 tubing between the air horn and the choke plate to hold the choke plate open while you move the throttle from idle to wide open. You should hear a ‘click’ as the fast-idle cam loses contact with the fast idle screw and the throttle plates should return freely to their fully-closed position. This is actually my preferred method of holding the choke plate open so you can set the throttle plates...



Yes, that's actually a short length of toilet paper roll. I mean, who can't find one of those in a pinch

From there, use a screwdriver to unscrew (counter-clockwise) the idle speed adjustment screw to the point where it loses contact with the linkage. Then, from the point that the idle speed adjustment screw just makes contact with the linkage, slowly turn the adjustment screw in (clockwise), counting in at least 1/8th turn increments, until just the very outer edge of the first progression hole is exposed and take note of how many turns were required to get there. On the 32/36 DGV, the plate should be just shy of uncovering the edge of the “S” port, which will be a much smaller port off to the side of the larger progression port. Notice how this is illustrated in this photo, it should look similar to a crescent moon, something like this...



This screw setting, what ever it may be, is considered your absolute maximum idle speed screw adjustment and can not be exceeded when tuning otherwise your performance and mileage will surely suffer.



This photo shows just how much of the progression hole is exposed with the idle speed screw turned in only ¾ of a turn. It’s easy to think that a ¼ turn doesn’t really mean much but it makes a big difference, as you can see. This is why Redline so strongly emphasizes the importance of the idle speed screw setting.

For a Weber 32/36, this screw setting should be no more than 1 ½ turns in. For a Weber 38, it will be no more than a ½ turn in. When this screw setting is exceeded, the engine will pull from the progression circuit rather than the idle circuit and will likely have a rich or stinky idle and the engine will often not even respond when the mixture screw(s) are adjusted. This is an indication that a larger idle jet is needed. Conventional wisdom might suggest that "it's rich so I need smaller jets." That, however, isn't the case.

This maximum setting is crucial and a properly sized idle jet will allow your engine to idle without exceeding the above mentioned screw settings.

There are plenty of topics to discuss here like float level, lean-best idle, idle jet size, fuel pressure, ignition requirements, etc. and I know there are some really sharp Weber guys on the forum so hopefully we’ll get some great discussion on here.

Shawn

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Last edited by swatson454; 06-14-2010 at 03:53 PM..
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Unread 06-18-2010, 12:48 PM   #2
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Quote:
Originally Posted by swatson454 View Post
This photo shows just how much of the progression hole is exposed with the idle speed screw turned in only ¾ of a turn. It’s easy to think that a ¼ turn doesn’t really mean much but it makes a big difference, as you can see. This is why Redline so strongly emphasizes the importance of the idle speed screw setting.
Shawn
Thank you Shawn....
The success that I have experienced tuning Weber carburetors has come from this enrichening hole not being exposed adding tooo much fuel at idle. Not exceeding the MAXIMUM idle speed screw setting and/or ZERO vacuum at the “S” or distributor ported vacuum advance. This point seems to be the “trick” when setting up a Weber.
Thanks
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Unread 06-18-2010, 06:06 PM   #3
2GPS4ME
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Not exposing the enrichening/progession circuit hole makes sense, however...

Isn't the 32/36 supposed to be a 'modification' to a 258? If so, then why in the world do so many people have issues with the Weber being supposedly jetted too lean (according to the Weber instructions)?

Example: I've heard of many people who have their baseline funamentals perfect (timing, no vacuum leaks, fuel pressure fine), but CANNOT get the 32/26 to idle until the mixture screw is anywhere from 3-5 turns out.
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Unread 06-18-2010, 06:35 PM   #4
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Quote:
Originally Posted by 2GPS4ME View Post
Not exposing the enrichening/progession circuit hole makes sense, however...

Isn't the 32/36 supposed to be a 'modification' to a 258? If so, then why in the world do so many people have issues with the Weber being supposedly jetted too lean (according to the Weber instructions)?

Example: I've heard of many people who have their baseline funamentals perfect (timing, no vacuum leaks, fuel pressure fine), but CANNOT get the 32/26 to idle until the mixture screw is anywhere from 3-5 turns out.
The 32/36 can be a 'modification' to a 258 but we have to remember that it was originally designed for a 2.5 liter engine, not a 4.2.

This increased demand that's placed on the idle circuit by its installation on an engine that's double the size for its originally designed and intended use can wreak havoc on a less-experienced tuner.

Like the Redline set-up documents say, if the idle speed screw setting isn't exceeded, a mixture screw setting of more than 2.5 turns out on a 32/36 DGV is a strong indication that a larger idle jet is needed on the primary side.

Redline assembles these carbs with a good, average-use idle jet and then supplies the screw setting absolutes and procedure to help the end user determine if a larger or smaller idle jet is needed for his particular application.

Shawn
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Unread 06-18-2010, 07:52 PM   #5
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What I'm referring to is not the carb itself, but Weber's entire conversion kit.

I noticed that there are multiple conversion kits with the 32/36 on Weber's website, two of which are not intended for the 4.2. I wonder if some dummy just found a random carb & threw it on, because mine is a slug.

I have not pulled my jets to see what sizes they are yet.
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Unread 06-18-2010, 09:37 PM   #6
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Hey Shawn...good topic.

I'm still trying to get my 32/36 "right" with McMud's and your assistance. You guys have been very helpful and more than patient with me and I appreciate that.

I'm whittling things down and right now my biggest issue is I can't get it to idle smoothly. It 'wanders' between 400 and 1K rpm. If I cup my hand over it, the idle picks up and smooths out. McMud explained that doing that is just like choking it.

Any suggestions?
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Unread 06-18-2010, 10:39 PM   #7
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IdahoJeeper, it looks like you and I need to check our idle jets.
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Unread 06-21-2010, 01:56 PM   #8
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Quote:
Originally Posted by 2GPS4ME View Post
Not exposing the enrichening/progession circuit hole makes sense, however...

Isn't the 32/36 supposed to be a 'modification' to a 258? If so, then why in the world do so many people have issues with the Weber being supposedly jetted too lean (according to the Weber instructions)?

Example: I've heard of many people who have their baseline funamentals perfect (timing, no vacuum leaks, fuel pressure fine), but CANNOT get the 32/26 to idle until the mixture screw is anywhere from 3-5 turns out.
I know the REDLINE conversion kit comes with “various” modifications. The jetting that they supply functions very well “when” the tuning procedures are followed. The jets they use are a 75 pri idle jet, a 60 sec idle jet 145 main jets and 170 pri air jet and 160 sec air jet. Typically the problems come when we don’t have this base line jetting and or vacuum leaks. Check to see what jets you have, then the set-up (speed screw, idle screw settings) and let us know what you find. There are many VERY knowledgeable tuners on this forum who will be more than happy to jump in and tell you everything they know.
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Unread 06-21-2010, 05:41 PM   #9
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ok, i've got some great feedback from swatson, but i need one more question answered. i was looking to order some jets based on feedback from clifford performance guys. itold them my set up and my intention to stick w/ the 38 weber over the 32/36( i have both ). the guy i talked to told me b4 i even consider changing jets, to get a redline large diaphram fuel regulator. he said the holley low pressure ( which i have ), mr gasket, or other small diaphram regulators are probably a main source of my frustration. he said it will give me the flat spots that i told him about. my concern was that i still may need to up my idle jet based on threads about rich/ stinky smell that wont go away w/ adjusting the mix. is this a sale pitch, or is there truth to the regulator?!?
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Unread 06-21-2010, 05:43 PM   #10
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just posting up. i have a thread in the YJ section talking about the weber 32/36 tuning. hope this can help some people. have some good info from McMud.

http://www.jeepforum.com/forum/f12/c...-36-a-1040957/
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Unread 06-21-2010, 06:23 PM   #11
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Well, as swatson454 originally posted, I found 'the spot' in my idle speed screw where the progressive port is exposed. I did not pull the carb from the manifold, but....

Long story short, I couldn't get it to idle right, even with the idle speed screw in quite a few turns.

After sloooowly turning in the idle mixture screw (until it was about 2-2.5 turns in - recommended setting), I unscrewed the idle speed screw, and VOILA! She started purring like a kitten.

Good information, swatson454!
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Unread 06-21-2010, 09:05 PM   #12
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GPS....maybe we are on the same wavelength. I went through everything (including setting float levels) again, and I too hit the "sweet spot". My idle was little low so I dialed in 2" of vac with the speed screw...now it idles great and it pulls even better.

A major improvement is to swap in a '79 dizzy if you've Nuttered. Gives you 2x mechanical (centrifigal) advance.

Swatson....thanks for all your help!! I appreciate it!!
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Unread 06-22-2010, 07:55 AM   #13
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Thanks guys!

Like uptillnow said, the throttle plate position is the trick to setting these up and everything you do to tune the carb will stem from there.

Now that you've found the 'sweet spot' and you know the enrichment holes aren't exposed, you can use the mixture screw setting at lean-best idle to determine whether a larger or smaller idle jet can be used to find improvements in either power or fuel economy.

I'm very pleased that the information has been useful. Thanks for your input!

Shawn

Edit: I forgot to answer an important question from usa.

I don't have a problem running regulators, per se. My main concern is running the $30 units. If your luck is anything like mine, if there was one faulty unit that made it through the production line, that's the one I'm taking home with me and there are a lot of faulty units with those things. Setting them at 3 psi in the driveway is a different scenario than driving up a long grade and, unless you have a pressure gauge mounted in the cab, it can be a whole bunch of fun figuring out what the heck it's doing and when.

You seem to have two options with a Weber and personally, I prefer the $14 upgraded Viton-tipped needle valve. That valve will handle all of the fuel pressure that your stock pump will deliver. The other is to run a regulator but reliable ones can get expensive. I ended up dropping over a hundred bucks on a Barry Grant bypass unit on a 383 because I was sick of struggling with the cheaper units.
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Last edited by swatson454; 06-22-2010 at 09:51 AM..
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Unread 06-22-2010, 10:05 AM   #14
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How about some general terms and definitions:

When you look down the throat of the carb (engine off) and have someone press on the gas, do both of the butterflies open at the same time (Weber 38/38), or does the passenger side open 2/3 of the way before the driver side starts to open (progressive) (Weber 34/34 and 32/36).

The terms DGV, DGEV, DGAV: D is down draft, G is the mounting direction, V is manual choke, EV is electric choke, AV is water choke...

In addition, on the 32/36 progressive carburetors, there is an overlooked adjustment that is recommended in the Weber rebuild manual to prevent a stumble when the secondary is opened. Basically, you need a small amount of vacuum or you will stumble when the secondary opens (IIRC the manual calls for 0.05mm opening and I was told by the guys at carbsunlimited to open it 1/6 turn or so) ...and if it is open too much you pull fuel from there during idle...

The secondary is the side that stays closed until 3/4 throttle (or there abouts) and then opens up. If you follow the linkage over (remember this is the barrel closest to the master cylinder) you can see where the linkage hits the "stop". This is the underside of an adjustment screw (flat head) that can be used to adjust the resting place of the secondary linkage. Back this screw off until the linkage no longer touches it (secondary throttle plate fully closed). Then advance the screw approximately 1/6 to 1/4 turn in from first contact with the linkage. This will allow a small vacuum to be pulled through the butterfly (to prevent vacuum stumble); but, not enough vacuum to affect the idle circuit.
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Unread 06-22-2010, 10:47 AM   #15
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Quote:
Originally Posted by 2GPS4ME View Post
IdahoJeeper, it looks like you and I need to check our idle jets.
Did you guys ever find out what size your jets are in your carburetor?
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