Weber Jetting Survey

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File removed

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Uploaded a new Weber Jetting database later in thread. Thanks,Hyde

[Rick Parker]

How much of this is affected by base Altitude? .....I'm sure it is to some degree.
Also a roller cam with the same timing specs as a flat tappet cam will be able to use a smaller jet, because the faster valve action will cause quicker depression within the inlet tract.

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It would be great to have all this info to put side by side.

[Caprimaniac]

Dear fellow Weber drivers.....

I went racing this weekend, and this time I really felt like converting to injection....

I had some big troubles getting the engine to drive properly; it was stumbling and clearly some of the cylinders didn't fire as or when they should.

I friend came up with a theory that the carbs were struggling to get enough fuel and that larger inlets to the float chambers were needed. We are talking needle valve & seat. I have seen little discussion of this here. And I couldn't find it in 13's great little table either.

A look through my setup show the needle & seat are 200.
As far as I can tell, these are the smallest type for the IDF's (200, 225 and 250 are listed in the partslist I have).

For IDA I find 200 and 300 + they also have an inlet ball valve whereof 16 different are listed.

Another cause for the Webers not doing the job right might be high cornering forces: We were pushing 99- 100% (ending out in the sand) going in powerdrift with Michelin racing slicks.

The engine has caused me headscratching before not doing as expected while going around the track; loosing mid- rpm out of the corner punch is not very funny!

I'd be thankful for any input on the matter.
(I'd like to add that my idle quality was not 100% with at lease 1 carb out of sync, which migth have caused some of the trouble. Anyway, the car went as a rocket in high RPM straightline; 7800 in 4. equals somewhere like 250 km/h)

By the way, it almost ended like thisRøykfull gatebilfestival | sa.no but luckily, we did put in a new windscreen later that evening.
Rock on!

[Caprimaniac]

Just a quick update on the troubles above.

What I found after some checking was: Left side plugs: all 4 dark brow/ black on the RHS all 4 plugs were light brown/ white-ish. I have a fuel regulator splitting L/R in AN6 lines at the rear of the carbs. Could this be due to sideloads (g-forces)? Is it possible???

[Gaz64]

Rune,

Run the smallest needle and seat that still gives maximum power.

You can get 1.75mm up to 2.5mm in 1/4mm steps.

If you are on an oval and only turning right, it may explain your richness on the left bank.

You may need to machine up some spacers to emulate a canted intake manifold, with the carbs leaning towards each other.

The main well and the discharge nozzle are line with the centre of the float bowl volume, and it would be difficult to overcome your problem any other way.

The float hinges from one side and will have more closing force on the valve with the fuel stacking up on the other side of the carb, thus giving a lower "fuel level" at the nozzle. The reverse is true for the other bank, thus one bank rich, one bank lean.

[Caprimaniac]

Very good advices, GAZ. Maybe I can set the floats on the LH side somewhat lower to overcome the problem. Tllting is possible, but alot of work...

Since my fuel- lines are figured as a T (ending at the front of each carb bank) I think that if the problem lie in the lines and the amount of fuel in the two banks, a connection at the front might do some good as well.

I looked at the Redline Weber webshop and I found the largest needle & jet for the 48 IDF available was the 200... (Although in my not- updated catalogue they are listed up to 250, as you mention, GAZ.)

Here we have a picture showing the plugs (4LH/ 4 RH). Quite consistent, or what?

[Caprimaniac]

Snakebiter; yup- you are correct- I do have a R/L linkage problem as well. It might explain it all. I will look into it today, and hopefully check plugs & all before the weekend.

13; I cannot remember seeing you testing A/F ratio? It's very useful as to get the webers correct. Hesitation at either RPM can be due to too much or too little fuel. It is also possible to trace the problem by reading plugs.

Changing the pump jets (exhaust) to 00 I think is mandatory... See Eljaro's posts on this.

[Gaz64]

Rune,

If you start experimenting with the LH float levels to get the power mixture correct, it will be lean in a straight line and give you a flat spot coming onto the main system.

Here's another idea: custom floats for all 4 carbs.

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Originally Posted by Caprimaniac

13; I cannot remember seeing you testing A/F ratio? It's very useful as to get the webers correct. Hesitation at either RPM can be due to too much or too little fuel. It is also possible to trace the problem by reading plugs.

Changing the pump jets (exhaust) to 00 I think is mandatory... See Eljaro's posts on this.

As of yet I have hooked the motor up to an A/F machine. Reading plugs at this point, learning the hard way

[Gaz64]

Reading spark plugs will only give you an average indication of A/F ratio.

Lean at one end and rich at the other (or vice versa) may give a good reading.

You need a fast operating wide band O2 sensor gauge with data logging capability to pick accelerator pump accuracy (rich/lean), idle circuit/progression/main circuit overlaps etc.

[Snakebit]

My plugs looked good, light tan. But I was too lean above 3000 rpm AFR was 17. Went up 2 jet sizes to bring it down to 12.5. Reading plugs will get you close, but a dyno lets you zero in.

Take your distributor to some one with a Sun distributor machine to recurve your distributor. You want a total of 38* all in by 3000 rpm. That was a surprize too. Jim Inglese said to run 20* initial advance and 18* in the distributor for a total of 38*. Also keep the fuel pressure at 2.5 psi

[dlampe]

I disagree with the 00 pump jet. Engines are different and have different fuel requirements. Mine bogs with the 00 and with the .55 but runs great with a .40. I have tested about every possible combination of jets, e-tubes and exhaust jets and that is what is making my engine happy.

[Rick Parker]

Copied (and edited) from Holley site but says it pretty well, regardless of carb type....Webers or Holley

The main or high-speed air bleeds (Air Correctors in case of Webers) affect the entire range of the main-metering system. The purpose of the main metering system and main air bleeds is to emulsify the fuel before entering the discharge nozzle to be discharged into the air stream in the venturi. The fuel/air mixture
becomes leaner as air bleed (Air Corrector) size is increased. Decreasing the size of the main air bleeds (Air Correctors) will decrease pressure across the main jet, which in turn will pull more fuel through the main system creating a richer fuel/air mixture. The main or high speed air bleeds also act as an anti-siphon or siphon breaker so fuel does not continue to discharge or dribble into the venturi after airflow is reduced or stopped. At high speeds the fuel/air
mixture must be on the rich side to prevent damage to the engine.
The idle system supplies fuel at idle and low speeds. The idle system requires a richer mixture than at cruise speed. Unless the idle mixture is
richer a slow and irregular combustion will occur known as a rough idle. Decreasing the idle air bleed size richens the idle mixture by increasing
the pressure drop in the system. Increasing idle air bleed size leans the idle mixture by reducing the pressure drop across the idle air bleeds.
The same conditions can be created by backing out the idle mixture screws, which will increase the pressure across the idle air bleeds, pushing
more fuel from the idle well creating a richer fuel/air ratio. The Idle mixture screw is the only adjustment recommended for controlling the idle
fuel/air mixture richness or leanness.

[Caprimaniac]

To update my previous L/R problem I did the following:
1. Undid both idle set screws and made the engine idle by hanging in the linkage and trottle wire (800RPM).
2. I then synchronized/ balanced the carbs by adjusting L/R and fore/aft linkagees.
3. Set the idle using idle set screws to 1200 rpm. By then the carbs were no longer fully synchronized (because of different kinds of faults in the linkage system), but they will be when on throttle.

It gave the smoothest running I have seen so far.....

On the 00 exhausts, there are different opinions. I haven't fully experimented to see what happens when they're opened up... I just refer to what I find in books etc.

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I'm Rebuilding the Jetting Database. If you have any changes or more info, please post them so I can update it. For those of you who have since joined the Weber ranks, please list your specs so we can build a library that is useful to the new enthusiasts who want to give it a go! If you have any other engines or know of any others, (I don't care what they are so long as you have the full specs)feel free to email me the details & I'll add to my list. Thanks, Hyde

[Tom Howland]

Thanks Hyde for doing this.
I'm running a 427W, Comp cam 35-425-8, @ .050 282/289,230/232, total lift .523/549, separation 110.
venturi 40, idle jet 65, idle jet holder 120, main jet 155, E tube F7, air corrector 170, acc pump jet 40, by pass 00, idle screws 1 1/4 turns.
Currently the idle is rich, transition is lean and mains are lean and there is a stumble at acceleration.
I use an an A/F meter and own about a pound of brass jets.

I've been working on these for a year now and have made some progress but I am not there yet!
A big discovery for me this last 2 weeks has been (thanks to jhirasak) the 25mm needle valve height. 3 of them were so far off I had to put them in a lathe and shorten them. I also installed sealed bearings (thanks to big deuce). I flowed them with a shop vac and made a tool to twist the shaft on one carb. I plugged a transition hole and redrilled it (thanks to big deuce). The bell crank is off center 3/16 in. so I'm going to weld it closed and redrill. I have a center bell crank that has the linkages coming from under the butterfly shafts. I would like to change that configuration to have the linkages above the shafts so it is easier to adjust. Does any one have that configuration? I would love to see your pictures.

[Rick Parker]

[IMG][/IMG]

Try to keep the pull arms as level as possible (there will be some arc, try to minimize it). The arms must be parallel, and the same length. In my case the pivot point for the bellcrank had to be moved rearward about 3/4"". I used a piece of 1/4" thick aluminum.

[jhirasak]

Hyde,

Please update the information that I provided earlier to you. I am currently running a Windsor 331 roller block with a Comp roller hyd cam XE282HR-12 with the following specifications: Gross valve lift .565 In/.574 Ex; Duration @ .050 232 In/240 Ex; Lobe separation 112.0 degrees. Ignition setting: 18 deg initial, 38 degrees total @ 3000 RPM.

The 48 IDA specs are as follows: Venturi 37 mm; Idle jet 70; Idle jet holder 100; Main jet 135; E-Tube F11; Air Correction 120; Acc Pump bleed 50.

The engine runs without flat spots after it warms up and get around 15 mpg on the highway and 10 mpg around town.