Weber Jetting Survey

[ack fia]

I was playing with an Air / Fuel Ratio meter on my 347 with Webers. I put the Oxygen Sensor about a foot from the header flange in the 3" collector of the ERA system. Testing resulted in a change to the idle jet from a 65 to a 60 and a pretty flat 14.6 fuel curve. It runs really good now. The car likes no filters and open pipes.
On the dyno you can see the accelerator pump contribution.
Pat

[desmo]

I tried this setup today : choke 40 mm, main jet 155 (also 160 and 165), air corrector 120, emulsion tube F11 (also F14). It doesn't work ! The idle is correct, but the engine farts between 1500 / 4000 RPM, with small flames... Any idea ?

[Eljaro]

that is the float level which is incorrect.Adjust that before you do anything else. If the fuel level inside the main well is too low or too high it will affect the emulsifying of the fuel at midrange and you will get what you have now. Now the idle circuit is fine and the main jet probably also, but everything in between, which is managed by the emulsion tube is not operating The Webers do not come adjusted properly from the factory.
Check for aiir leaks around the intake
Also make sure ignition is correct. 12º initial is too little for Webers. More like 20º is best.

[desmo]

I adjusted perfectly the float level last week (5,5mm & 24mm) and I made several tests with the ignition. I don't understand anything !

[Snakebit]

1.20 Idle jet holder is too lean. Try a 1.00 with a 65 f10 idle jet.

[dlampe]

I will chime in here with my current setup. It seems to be working fine right now as tested with the LM1 A/F meter.

462 Aluminum Pond block. 10 deg. canted intake.

Chokes 40mm
Idle holder 100
Idle jet 65
F7 tubes
4.5 Aux venturis
Mains 170
Air correctors 150

Floats are set to 4 mm with a 24.2mm needle/seat measurement.

I am still testing so this could be a little rich but safe.
Roller cam
Dur @ .006 is intake 303, exhaust 311
Lift is intake 654, exhaust 649
LSA of 112

[ack fia]

Am I missing somethig here or is the Main FUEL JET suppose to be SMALLER than the Air Corrector?

[Snakebit]

From what everyone is finding using the f14, f15, & f16 emulsion tubes, the air corrector jet is 110 t0 120 and the main jet is 150 to 165.

[priobe]

Just out of curiousity, not that it makes a difference, but how many of you have successfully tuned a Weber setup on a BB Ford on multiple motors. I have not but it obvious to me that they are not all the same from these post.

How many of you have tuned Weber carbs successfully? Meaning with no more needed adjustments or if adjustment is needed you know exactly why the adjustment is needed.

The reason for these questions is because unless you understand from the begining that this is going to be a learned process of tuning these carbs, then just put a 4 bbl.

I have seen suggested setups with people constantly complaining that it does not work!

Well I am convenience that either no 2 motors are tuned with the same setup or no two tuners are doing the same thing, i.e. mixture screw idle sync of carbs and so forth. I will favor both of these options.

I agree you can get it in ball park but many are having trouble seeing the game.

Personally, I think (1) get your tuning at idle correct. dont worry about wide open throttle right now. Get you car to run right. This is where you will spend 98 % of your time.

Play with Etubes, idle jets , idle holders and main jet
Hint: The larger the idle jet, the richer the mixture the longer the circuit will be engaged.

I personally would not run anything smaller than a 40 mm choke (period)

Pump jet jets are 4.5

Exhaust (at the bottom of the bowl), start off with a 50/ 55. The the ultimate goal here is to not rely on this circuit so the higher the exhaust number the better the tune is becoming. You can use this circuit to mask alot of your problems, however everytime you touch the throttle there is added fuel being delievered.

Idle jet, if you have 55 try it, then move up to a 60 or 65. This will depend on (1) your eTube (2) your main jet. Keep this in mind.

Select your idle jet and you idle jet holder.

Idle jet holder (air) start off with a 70 and open it slightly in .05 increments. Rich to lean

When doing this make sure you remove your main stack so that your car dies around 2200 - 2800 depending on the size of idle jet. The larger the idle jet the longer the rpm range. Remeber you want your main jet to slightly overlap you idle jet

now that you feel you got the feel for how and when the circuit behaves move to your main circuit. Here is a simple BASE formula for main jet choke size x 4 (round up to nearest value of jet). This is pretty much all teh books

Then play with all the Etubes you have. I personaly like the F11 Tube, then F16.

Concentrate on the Etube this will help you dramatically. Many books say that you need a dyno for changing Etubes. I think you can clearly see the difference from tube to tube.

Air jet, put the biggest one you can find on hand. Dont worry about this one right now. But dont step on it either. What you want to do is take you time when tuning these carbs. You are not going to find the magic setup and floor it and be happy.

After you get drivablility and idling good / very good. You should have a grip as to how the system works.

Air corrector you can then use a LM 1 or some other analyzer to to see your fuel ratio.

Again your floats have to be correct, linkage has to be correct and mixture screw has be tune correctly.

Again what I am saying may not work for you but it works for me and I am nolonger complaining about these carbs, nor am I afraid of them. I have invested a ton of money and time teaching myself these cars to my motor to my car resulting in my satisfaction.

I am simply passing on approximatly 3-4 years of my experience with the hope of help others.

Finally most important, I can not stress this enough. warm up the motor!!! My motor runs great but when it reaches optimal temperature what a different motor, different sound, and now its time to let those Webers sing!

Also remeber, temperature, altitude, gearing, cam, ported heads and many many more may play a role in the jetting. So you may not get a direct dial in from 1 motor to another.

[priobe]

The above thread is not to insult anyone. It's just the new weber people or people with existing problem will receive alot of different information and I remember when I was in their shoes and I am still learning the carbs. However now it's different because I am having fun with them.

I am just trying to help those that might think like me.

Enjoy!

[Tom Howland]

Well thank you priobe.
These are the best directions I’ve seen. I’m installing a new motor with new webers and hope to fire it up in 5 weeks. I’ll have the headers finished next week. Then lots of miscellaneous stuff. I do understand the involvement the webers require. And am looking foreword to it.

[Snakebit]

Mine was trial & error. These carbs will tell what they don't like and scream when they are happy with the right combination. The standard set up everyone tells you to use 37 chokes, 120 holder, 65 idle jet, f7 tubes, 155 mains, and 200 airs did not work at all. Thanks to Inglese telling me to use f16 tubes and Eljaro about the 40mm chokes and which way to go with the jets, I was able to get on the right track and fine tune from there.

[priobe]

Tom,

I am glad I can somewhat help. And if you need any assistance or need to bounce ideas off of someone, please let me know.

[Eljaro]

snakebit

Thanks to Inglese telling me to use f16 tubes

are you still using the F16 tubes?
Are they perfect or do you have some part throttle hesitation?

priobe

Exhaust (at the bottom of the bowl), start off with a 50/ 55. The the ultimate goal here is to not rely on this circuit so the higher the exhaust number the better the tune is becoming. You can use this circuit to mask alot of your problems, however everytime you touch the throttle there is added fuel being delievered.

I have found that with a bypass for the pump jet the engine just falls on its face if you snap-floor it. I ended leaving the bypass close (0.00) because of this. I can floor it instantly in any gear at any speed and it will instantly shoot forward or spin tires.An incredible reaction which has surprised many who have driven with me and used to fuel injection supercars.
No way to get that response with bypass in the bowl.

[priobe]

Originally Posted by Eljaro

snakebit


I have found that with a bypass for the pump jet the engine just falls on its face if you snap-floor it. I ended leaving the bypass close (0.00) because of this. I can floor it instantly in any gear at any speed and it will instantly shoot forward or spin tires.An incredible reaction which has surprised many who have driven with me and used to fuel injection supercars.
No way to get that response with bypass in the bowl.

Eljaro,

I dont doubt that the 0.00 works for you, if it does work for your situation. Maybe its the altitude, your cam, or something else. I am just saying that with my experience with my setup I have tried the 00 and mine bogs down. When I have the 55 in it, it is perfect as you described. I will pull my jets tonight and explain my exact values. I am not exactly sure what my air and main are.

[Snakebit]

If I take it easy on the throttle, the transition is very smooth through the gears. If I am crusing along at 2000 rpm and floor it it bogs down and then takes off like a rocket. I am running .35 bypass jets. Change out to 00 or 50???

[priobe]

Snakebit,

I too have experience that same problem with .35. I am running .55 and it help clear my problem. From what you are describing I would put in the 50.

[Snakebit]

Eljaro, still running the f16 tubes. Thanks, John

[*13*]

My setup on a 289 (294CI) is:
48IDA WEBERS
Choke 37mm
Idle fuel jet 65
Idle jet holder 120
Main fuel jet 150
Air Corrector 120
Emulsion Tube F7
Accel. Jet 50
Screws set at 3/4 turn
CAM
Lift .468/.462
Duration @ .050 229 / 236
Lobe Separation 112

Sorry for the late add on this. It's something I've been meaning to get to for some time. I just changed out my MAIN & IDLE jets & the car is running a lot better. I will likely need to change out the air correctors, but at least I've got her within range now. This thread has been helpful, thanks guys! Someone should post a database only, without commentary, spreadsheet? The commentary is also very helpful. Would just be nice to see all the numbers side by side. The one thing I would add & reiterate here is that matching the main Jets to the Venturi's should be the place you start with these carbs. If you look at all the numbers people have posted here you'll see that this is a fairly consistent value. The the main jetting vary a size up or down from this but for the most part they have a pretty tight range. Like a Holley 2 or 4 barrel, there is only some much fuel that can be sucked out with a specific venturi size & oversizing the jet beyond reason really isn't going to get you too far. Picking your idle jets is fairly easy from that point, just go back to the list here & make a guess based on what you see. You should be pretty close. Second thing I'd do is get them sync'd up. At this point you should be ready for fine tuning. Hope I'm not over stepping anything here. Just a lot of back & forth info when you read up on these carbs. It gets so confusing that you feel like you might need a 4 year degree in webers before you start. If you understand the principals of a carburetor I believe this multiple carbs is just the next step & Webers are just a carburetor. Use "carburetor common sense" & you should be able to handle it.

[*13*]

I put together a spreadsheet with all the jetting info here. A couple interesting things jumped out of those who submitted enough info. Based on the Etubes, most of those runnin F7 tubes had an overlap bigger than 110. Second, & this mostly applied to the small block guys because the cam info had been given, but those using F16 tubes were also running bigger venturi's 40-42, bigger main jets, avg slightly bigger idle jets & had 110 overlap. It'd be really interesting to get all the cam info from everyone to see what else jumped out.