Weber Fuel Levels - Alfa Romeo Bulletin Board & Forums
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post #1 of 6 (permalink) Old 09-13-2016, 09:18 AM Thread Starter
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Weber Fuel Levels

There is conflicting information published on the correct fuel level in the well of a DCOE. I am aware of the procedure to set the float height but I can never get it right and I prefer to measure the level of fuel in the well. Several sources say 25 mm from the top of the well but that seems too high since the distance to the bottom of the nozzle is 23 mm and that leaves the static level only 2 mm below the nozzle. The Weber tuning manual says that the level should be " not more than 5 to 6 mm" below the nozzle. John Passini says that the level may have to be a little higher in 45's than 40's but he does not give a reason. I have also read of raising the level a little on 45DCOE152's to help get over the lean stumble but I don't see the logic in that. A higher level will bring in the main circuit a little sooner and fatten the transition mixture but my stumble is much lower down the rpm/power range.

I could try 4 mm below the nozzle and see what happens but I would love to hear that someone else has already done this and has some data.
Thanks.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke

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post #2 of 6 (permalink) Old 09-13-2016, 11:41 AM
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28mm, Ed.

If you need to rich up transition @ very small TP angle, you can go down to 27.5.
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Last edited by hunttheshunt; 09-13-2016 at 11:45 AM.
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post #3 of 6 (permalink) Old 09-15-2016, 03:21 PM Thread Starter
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Thanks, they are now at 28 mm. One was too high and the other too low.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #4 of 6 (permalink) Old 08-25-2019, 04:36 PM
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Originally Posted by alfaparticle View Post
Thanks, they are now at 28 mm. One was too high and the other too low.
Ed, is 28mm the depth of fuel in the float chamber? from the bottom of the chamber to the fuel level? Ours is measuring 35mm, and the float static dimension is 8.5 mm as measured holding the upper chamber vertical and measuring from the gasket surface to the brass float.
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post #5 of 6 (permalink) Old 08-25-2019, 06:37 PM Thread Starter
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28 mm is the distance from the top of the well to the fuel level. The nozzle which is the outlet for fuel emulsion from the well has a lower level of 23 mm from the top and setting the static level at 28 mm means it has to be lifted 5mm before the main circuit comes into play. If you look carefully down the well you may be able to see how far is the fuel level below the nozzle and you may be able to measure it with a depth gauge.

Ed Prytherch
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76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #6 of 6 (permalink) Old 08-25-2019, 07:58 PM
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I’m working from memory here, as I just discovered all of my old Weber manuals were stored in the leaky section of the hangar. Dang.

Anyway...

My recollection is that the float level was specified differently for different cars. I believe there to be four primary variables:

The vacuum level created by the engine. This can be significantly varied by cam profile, overlap, cc, etc.
Aux Venturi size, and
Primary Venturi size
Emulsion tube used

Thus, if you’ve hotted up your engine from stock, the stock float level may not work.

The float level primarily determines at what RPM the main circuit tips in, acting in harmony with the E-tube.

My recommendation is to experiment first with float level changes before messing with E-tubes.

You can determine the idle circuit upper RPM limit by removing all four E-tubes, and going for a slow drive on just the idle circuit. Slowly accelerate until you sense the power has peaked. That’s where your idle circuit has rolled off.

Start with whatever E-Tube you think is right, and the float at 28 mm below flat surface around E-tube wells. Accelerate smoothly. If you get a steady increase in torque, you’re probably good. If you feel a slight slump around the RPM limit for your idle circuit, raise the float level one or two mm and try again. It should feel good with the float level somewhere between 24 - 29 mm, or you’ve got other jetting problems. Your mains and airs ought to be close to what the various charts recommend. The E-tubes are the mystery. Generally, F16 will work, but give you a rich transition.

You might get connected to Keith Franck at “sidedraftcentral.com.”

Don P
Carson City, NV

Past Alfas...
59 102 Touring (first Alfa $500 running)
65 Sprint GT (2nd Alfa, $500 daily driver)
102 Sprint (never did anything with it, but wish I had)
74 Berlina (first new car - now certainly rusted into oblivion)
61 Giulietta Spider G-Prod Race Car (where is it now?)
84 Spider Veloce (rarely drove it, so sold it)
86 Quadrifoglio (Dull car - no more 115s for me)
1971 Montreal "The Full Monty". Fair winds and following seas

Current Alfas
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Oops. Add to the "present" list, 10204 01488, 2000 Touring Roadster project

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1955 Cessna 170B (wife taught me to fly tailwheel in this)

And present...
64 Mooney M20E ("Rambo". My faithful steed for over 40 years) Over 55 years old, and just returned from a trip to Argentina in him
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