Webber 38/38 38 38 38,38 Stolen info from http://www.jeepforum.com/forum/f8/weber-set

Weber Set-Up and Tune Discussion - JeepForum.com
This needs to be here and saved, pinned, usfull info, Thanks to swatson454 for this thread!!!!!
Posting is obviously for Jeeps, but very good insight on the carbs

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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...

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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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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...

Now that we've had some good discussion on the importance of the throttle shaft's position and the carb has been mounted in a manner that will prevent an air leak, we can move on to setting the mixture screws and using their position to determine a suitable idle jet size.

With the 38 DGES, I like to turn both mixture screws in clockwise until they lightly seat and back them out two turns for my starting point. Start the engine and let it warm up, making sure the choke is fully opened. We're looking for the smoothest running engine speed that we can obtain without using the idle speed screw. Begin adjusting the mixture screws inward in ¼ turn increments, one then the other, then wait a few seconds and listen to the engine respond. 1/8th turn increments are fine, just remember to keep track of where you are. I often find it helpful to run a fast idle for a few seconds after each adjustment and then let the engine return to idle. The idle speed should begin to pick up and the engine smooth out. Keep going in this fashion until the adjustments do very little to nothing and then it actually starts to slow down or sound worse. Stop there. Now slowly back them out in 1/8th turn increments to the point where the engine sounded the best. This is considered to be the lean-best idle. Then, just make a note of how many turns out you are from its seated position.

If, at this point, you find the idle speed to be higher than you like, you can lower the idle speed screw to your desired setting, run through the mixture adjustment procedure again and be done.

If you found that the engine picked up by turning the mixture screws outwards, rather than inwards, beyond two turns on a 38 DGES, a larger idle jet will most likely be needed. A good quality idle speed found just less than 2 turns would be a good indication of an idle jet size that will provide you with good mileage.

For a 32/36 DGEV, lean-best idle being found at or near 2.5 turns out on the mixture screw means that the current primary idle jet size will likely provide you with good fuel economy. Beyond that though, is a pretty strong indication that an increase in idle jet size is needed on the primary side.

Selecting an idle jet where the lean-best idle is found with the mixture screw in the 1 3/4 turns out range on a 32/36 DGEV progressive and roughly 1 turn out on a 38 DGES will likely provide more performance and acceleration but could come at the cost of some fuel mileage.

Although it isn’t very common, it is possible to need smaller idle jets. The first indication of this will be a lean-best idle coming with usually less than a full turn out on the mixture screws on the 38 DGES and about 1.5 turns out for the 32/36 DGEV. All of this assumes that the Maximum Idle Speed Screw setting has not been exceeded and that you still have zero vacuum at the vacuum advance or ”S” port.

Most of these settings have been taken from Redline Weber's installation instructions.

Great discussion, guys. Thanks for everyone’s input.

Shawn

There is also the “Rich Best Idle” method which is NOT as desirable as the “Lean Best Idle”. This is usually achieved by turning the Idle Mixture/Volume screw out beyond the 38-DGES = 1 turn and the 32/36 DGEV = 2 turns, to the highest manifold vacuum or the richest smoothest idle. This method has NOT been desirable due to the excessive amount of fuel blowing out the exhaust. I have tried the “Rich Best Idle” procedure and then continued reducing the idle jet size bringing the mixture screw out farther than the parameters, “Redlines” parameters. My results created stumbles, fumbles, and inconsistent idle quality. This can't be good...

I always use the “Lean Best Idle” tuning method; this will also determine “the” correct idle jet and an all around good idle quality and running up to 2000RPM. THEN we can take a look at the main circuit fuel demands.
UPTILLNOW

Uptillnow, this has been my experience as well. I was unable to find lean-best with 45 idle jets without exceeding the maximum idle speed screw setting. That officially excludes the 45 jet from the lean-best, proper baseline tuning jet selection line up.

I was able to find lean best with the 50 idle jets roughly around 1 3/4 turns out on the mixture screws. Although the jet was beginning to show some weakness in the acceleration catagory, it was still a very useful jet (no hesitation, no lean stumbles, etc.) and returned good mileage.

I've found lean-best with the 55 idle jets right at 1.5 turns out on the mixture screws and the 55 seems to be an all around, good performer. It seems to have a good blend of fuel economy and acceleration. That may be why Redline assembles the carb with a pair of 55 idle jets

A pair of 60 idle jets came in somewhere around a full turn out on the mixture screws, IIRC. Although acceleration and throttle response was up, the mixture ratio was down. It was a really good performer without being overly wasteful.

The 65 idle jets were just sick rich.

When testing the 50, 55, 60 and 65 idle jets, at no point did I have to touch the idle speed screw to keep my desired 650 rpm idle. All that was needed was another run-through of the lean-best procedure.

Quick note: The addition of a header, upgraded ignition or plenty of other things will affect your final mixture screw setting to some degree so certainly don't take my numbers as a final. Like uptillnow stated earlier, your ignition advance settings will play a big role in your screw settings and idle quality. I run a little more initial advance, around 10* to 12* degrees; which Redline recommends, but I also use manifold vacuum as the source to my vacuum canister (we'll burn that bridge on a different thread). If I ran the 'normal' 6* initial advance and used spark ported for my vacuum canister, I likely would have had a hard time finding lean-best with the 50 idle jets and I'm certain that the air/fuel ratio would have been adversly affected on all of them.

I know mcmud has done the same idle jet tests with the 32/36 and I'm wondering if he had the same experience as uptillnow and I have.

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Originally Posted by mcmud View Post
Once you hear that occasional lean hiccup at say every 15-20 seconds you are at the point which is considered the Lean Best setting.
Nice point, mcmud. Using a wide-band monitor, I've seen that, regardless of idle jet size, the ever-so-slight hiccup you just mentioned always seems to begin around 14.5:1 air/fuel ratio. That's about as clean of an idle as you can expect from one of these old things. Wise wolves, you two are!

Shawn

Good comparison info! I used the 65 idle jets for winter and it makes my automatic car scream point a to b, timing advancd like 16 (b20a) but without having a wideband to catch the transitions under loads and wot I can't say Everything else is as well:). Sick rich yes but very smooth idle and 650 ish rpm. 55-60 much better all season jets.

Good stuff on here!

In my experience, doing the lean best idle does work great for finding your idle jet size initially. But my understanding is that the Main Jet still affects the mixture across the entire RPM range. So if you put in a bigger main, you still may end up richening your idle, and having to go back down a size on the idle jet, or at least re-tuning the idle screw at best.

For people I've talked to who are new to tuning Webers, I usually just suggest they get it running as smooth as they can on the stock jets. I don't think that they are far enough off to ever cause any damage to the engine, and that's quite a good start for most people who aren't necessarily trying to squeeze every little bit out. I think first timers need to tune the carb by ear and learn how the car feels when driving around. The AFR numbers are not as important as making sure things are smooth, and I think the first time you see a gauge in operation on a carbureted car, it just adds a lot of confusion.

If you are looking for a Wideband to have a little data for your tune, 14point7 makes a $30 controller that you build yourself. When I bought mine, they sold me the Bosch sensor for $50. So a complete kit for $85-100 if you're willing to put in a little work. Good, cheap project to work on your soldering skills.