Wiki Home \ Weber Carb; Guide and Troubleshoot

Weber Carb; Guide and Troubleshoot

Last Updated: Feb 24, 2015
View Photos

I think its justified to make this thread in the techie forum! It would not only conserve bandwidth because of needless new threads by others, but it would also be a #1 source for figuring out your carb problems! We should all be able to pitch in on this thread if need be, and definitely is a wise idea.

I could go on about tuning, installing, and rebuilding, but not right now, lol. I definitely would like to post this image though so any of you can figure what to do if need be! Here is a diagram of all types of floats found in the Weber carb:


Okay, I feel that pic is too blurry to understand! So I will explain a little to give you insight on how to make sure your float is working properly! Although, from Weber the carb is supposed to be set already! This is more of a means to make sure you carb is troubleshooted right! Proper float level means you will have good fuel consumption, which in turn alters MPG. It will also determine driveability and characteristics of your carb!

When your float bowl is full, the floats rest on the gasoline. This in turn will keep the power valve/main circuit from pumping gas into the float. When the bowl is low, the floats go down. When it reaches a low enough level, the float will then open the valve allowing gas to pump into the bowl! Making sure that your float is set correctly, will ensure you have a properly tuned carb!

Brass float: OPEN: 51mm from bottom of float to top of the bottom face of the carb. CLOSE: 41mm
Plastic float: OPEN: 51mm CLOSE: 35mm

IDF SERIES: OPEN: 35.5mm from TOP of float CLOSE: 10mm from TOP of float.

DCOE: This float is measured when GASKET IS IN PLACE with top of carb!
OPEN: 15mm from TOP of float. CLOSE: 8.5mm from TOP of float.


(Pulled this off of a previous post of mine. No sense in re-writing it!)
I hooked up my choke wire to the + terminal on the ignition coil. Works good! Just don't let your key stay on the ON position when the truck is off! Or else you will end up with a warm choke and a cold engine! I don't have any clue how it would burn the choke up. My Weber tech. guy told me that it was okay. So I think he is a little crazy, lol! Its up to you...

If your choke is engaged when you try and tune it and its not fully open, your tuning will be off because the butterflies limit the air for a proper mixture.

Okay around the Electric choke, there are 3 screws that hold it in. Now, if you loosen all 3, you can turn the white piece clockwise to loosen the coil, or counter-clockwise to tighten it. What you want to do, is in the morning when its the coldest, before you start the engine, push the accelerator in and let go. This engages the choke. This puts the fast idle speed screw onto the fast idle cam.

Remove your air filter and then loosen the 3 screws for your choke. Turn the choke until it opens up. Then tighten it again until the clearance of your butterflies is 1/16th of an inch to the venturi. Which is the clearance between the top part of the butterflies to the side of the carb. This gives it a good start for choke setting.

Start your truck up, and warm it up to normal operating temp. When you have the truck warmed up, push the accel pedal and let go to blip the throttle to dis-engage the choke! One thing to do as the truck is warming up:

-The fast idle speed screw should be turned in as you are warming the truck up so that it is idling at about 2000 rpm. Don't worry the next time you start it up and its idling at 1200rpm or so as its warming up. The fast idle cam is a lobe and the rpm will increase as the butterflies open. Although, after about 10 seconds, if it does not get to 2k rpm screw in the speed screw until it is.

The funny thing is how our chokes do not dis-engage once it hits the top of the lobe. Our carbs are'nt made like that...

SO! You have your truck warmed up. After blipping the throttle to knock the speed screw off of the fast idle cam your truck should be at its normal idling rpm. 825 is the ideal rpm four our trucks. Once you have dis-engaged the choke, the butterflies should not be close anymore. It should be nearly straight up and down. Its okay if its 5 or so degrees more closed. If its closed more than say 15 degrees, you need to loosen the choke so the 'flies are open a little more.

Be careful when you go warm up the truck again. After not running the truck after 6-8 hours, the choke coil should be fully cool. If you engage the choke again and the chokes clearance is not about 1/16th of an inch of clearance you need to set it again. It takes some time to get the sweet spot in the tuning of the choke, and let alone the mixes, etc.!

Fact of the matter is, the choke makes it a rich condition for your truck to run in the morning when its cold. Although, what should happen, is that the warmer the weather is the more the choke should be open. So it will correlate with the weather and run time, etc.

If you like, you can remove the 3 screws on the choke, and take the face piece off. If you look, you will understand how the choke system works! It will also allow you to check and see if the rod for the 'flies is set in the coil right.

ALRIGHT! SO, now your truck is warmed up! The trucks fast idle speed has been set, the choke is adjusted! The butterflies are open all the way. NOW, it is time to adjust your mix screw FIRST! Its a good idea atleast to have the idle a little high. It will help you tune the truck better. Really, all you do is follow what weber told you. If the mix is more than 2 turns you need to change your IDLE jets! I say 1000rpm is good enough to tune the carb right in terms of mixture. You want to listen VERY intently to how the truck runs. It should'nt go over 2 turns max. For every turn out thereafter is a jet change of another size.

The mix adjustment is determined by the weather; hot or cold, altitude, and type of fuel used. I filled up on 87 octane this time at a cheap gasoline store! I think its the first time I noticed how cheap, cheap fuel is! I had to turn out my mix screw a total of 4 turns!!! It still knocked, but it was the smoothest it would run. I had to buy some heet from the store, which is essentialy rubbing alcohol. It absorbs water or any other cheap additives of the fuel and makes it burnable. Be advised if there is water in the tank, the truck simply will not run!

Although, if you end up in a situation like mine, tune to the best you can, buy some additive, and buy 89 octane from a premium store! I will have to readjust my mix once I re-fill.

So now your mix should adjusted right, now its simple to adjust your idle! Turn the screw in or out until you get to what you think is 825. It won't be exact but thats okay! Make sure that if you screw it out, your throttle linkage is fully resting on the screw!

<i>Tuning; CONTINUED!</i>

I will be going into more detail about using some more modern tools to help tune your weber carb! To start off, I have found that having 2 more things to help tune your carb better will provide you better performance, cleaner emission, diagnosing the carb, and engine problems as well! How splendid!

I will be providing pictures soon enough of how this comes together once I finish my dash, haha! This will end up being an install on it all, which should probably be in its own techie... but it is more relevant to this.

First off, in order to tune your carb better you will need:

1. Air/Fuel mixture Gauge:

By doing so, you can then buy an 02 sensor and install it to the guage! The 02 sensor will then allow you to measure exhaust gasses. This in turn will allow you to adjust the mixture and jets of your carb through all phases of speed! Now you can see if you are STOICH with your air/fuel!

NOTE: STOICH is short for stoichiometric. This term is defined by a "perfect" air/fuel mix ratio of 14.7:1.

2. Vacuum Gauge

You may ask, what is the vacuum gauge for? Well, good question! The vacuum gauge is going to allow you to diagnose a SPECTRUM of things! Not only carb tuning, but engine troubleshooting as well!
Here, I provide you with a site that is going to explain it better than yours truly:

As for attaining the gauges, I have bought mine from an e-bay seller. If you wish to purchase yours from him as well, here is the link: They are small 52mm gauges that can fit just about anywhere! LED, and light up nicely!

I figure I may as well write some about this as well. When you are tuning, or refilling your tank, or the weather changes, especially altitude, your mixture can be off. More than enough to require a jet change!

I had to change jets once spring came! If you notice your truck is not running smooth and not idling like it should, or if your throttle repsonse is delayed, or flat, a jet change is also in need!

One way to know if you need a jet change, is if your mix screw is out more than 2 turns! If it goes out anymore then that you need a smaller jet. For every turn out after 2 turns max. you need to get a jet a size different. If you cant tune the carb right between the seat and 2 turns, you need bigger jets. Although, this jet change is going to only be for your idle jet(s).

You have:
1. Idle Jets
2. Main Jets
3. Air corrector Jets

-Idle jets apply from 0rpm-1500rpm or so.
-Main jets are from 1500rpm-3000rpm or so.
-Air corrector jets handle from then on in combination with your main jets.

If you experience throttle problems in these rpm ranges, this is what jets you are looking for. It takes some time to tune the jets right to get it perfect if you are experiencing problems.

-Your idle jets will be located on the sides of the carb where the float is at.
- The main jets are inside the carb. You would have to take the float out.
- The air corrector jets are loacted on top of the carb in an opening by the venturi.

Jets are about $7 a piece. So if you have problems, I would consult a shop that specializes in this in order to get you the right jet the first time! Otherwise, your better off buying the jet kit off of Redline.


This is in PDF format. You will need adobe acrobat reader.


Created By: hex0rz

Page 1 of 2
1dayiwill avatar
1dayiwill   +1y
Looking at this diagram, what can be removed when a Weber is added?

Will most of this vaccum stuff be unneccesary with the Weber?
What about the wiring harness that goes from the ECU on the passenger side to the intake manifold. Can that be removed?
Thanks, Ian
elbine69 avatar
elbine69   +1y
None of that vacuum stuff gets hooked back up with the weber. The wiring can be completely removed.
hex0rz avatar
hex0rz   +1y
Everything, and I mean everything can literally be taken out once the Weber goes in. You will need to have your vacuum advance hooked up, although.

From what I remember, you can have the option to leave in the charcoal canister and also hook up the EGR to the wber as well..

I do not know how the hookup for the EGR can be accomplished, though. Really, imagine your 4-banger with the weber as a 350 with an edelbrock. Just not so big and with all the horsepower. Essentially, what happens in the weber conversion is that you are "reversing in technology" and gonig back to a simple carb to deliver fuel and not recirculate the exhaust fumex, etc. to completely burn off for a cleaner exhaust...

Make sense?
1dayiwill avatar
1dayiwill   +1y
Indeed, does the Weber's instructions show how to hook up the vaccum advance?
hex0rz avatar
hex0rz   +1y
It will show where the port is on the weber to hook up the advance, yes... If you have any problems PM me!
nytrdr24 avatar
nytrdr24   +1y
nice tech article there hex!!! it ought to help a bunch of peeps out!
hex0rz avatar
hex0rz   +1y
Yes, well, it is a little depressing when you don't hear it, lol. Not that it matters much and all. Funny thing is, why type it all when you can go to the store and spend $15 on a Weber book that will tell you everything about them!

With mine, it will constantly change and expand. I learn things as I go, and will have to revise things. I only do it so that maybe if you read, you can avoid the same mistakes as I have encountered.

But, thank you for the appreciation NYTRDR!
dropped90(justin) avatar
dropped90(justin)   +1y
damn hexorz you back from the dead how you been?

hex0rz avatar
hex0rz   +1y
Hey 90, lol, no.. Work mainly, and on the side I just got done with the hunting season for this year.. And then fixing the truck a little on the side combined with family.. lol...

I'm doing alright, thanks for asking, lol.. I'm gonne be getting laid off in a couple months, I predict. So I will be bagging the truck then!
1dayiwill avatar
1dayiwill   +1y
What fuel pressure regulator are you running? How much was it?
Page 1 of 2