Weber selection and initial jet tuning

[blodi]

So my own self assessment is that the accel circuit has little to do with the wot pulls. It does impact drivability though. I’m going to put my leanest 65 exhaust pump jets back in.  I’m going to put the 140 mains back in to lean it up again.  I’ll leave the float level where it is as that seemed to have no impact either. 

[240260280]

Before you make any changes. What is your current fuel level?

 

What is troubling is the 3 point range of the WOT runs that we can not remove with E tube change or accelerator circuit.  The Venturi size or  ratio of venturi to throat (or fuel level) could be part of this seemingly untunable undesirable curve. It needs to be explored further.

 

FYI It looks like the accelerator pump circuit removal leaned the top end out  ~ 1 point.  The big dip at the first 1/3 of the WOT run is the gorilla in the room.  Hopefully fuel level lowering can remove it.

 

 

 

Edited June 4, 2018 by 240260280

[blodi]

What is the proper way to measure the fuel level? Remove the main jet assembly and put something down there to mark it? 

[240260280]

Yes. Here is a quick way to do it:

[240260280]

Here is another (pipet):

Edited June 4, 2018 by 240260280

[240260280]

Here is another (optical):

 

 

Edited June 5, 2018 by 240260280

[240260280]

(dip stick)

Or you can stick a wire tie down the main jet tube to the bottom then mark where the top of the bridge is and measure from it to the wet point.

 

Edited June 4, 2018 by 240260280

[blodi]

Fuel level is at ~31mm measured with caliper.  I pulled the jets then turned on the pump for a couple seconds to make up for the lack of volume of the jets. 

[240260280]

Good data. This may be why the WOT run is not flat for all Etubes.   Could you please raise the fuel to 27mm down and leave the existing parts in. It will enrich all circuits so be aware.

 

It  would be good to see what it does to the WOT shape before dialing back the fuel jets. Hopefully the shape will change.

[blodi]

So do I raise the float level 4mm to get to that point? Do they correlate like that?  

Wouldn't raising the fuel level make it richer overall? Just learnin. 

[blodi]

Found this info elsewhere... I've got the plastic floats....I had them at 14...now at 16.....I'll try ~12.5. 

Weber Redline bulletin circa 1985-1990

"the float height is set by bending the tab on the float ball.....The height 14mm is measured from the gasket to the top of the PLASTIC float, without the weight of the float depressing the ball in the needle valve. After setting float height, set float drop for 1.5mm of travel. (of float). Adjust by bending the tab on the float resting on the outside of the seat area.
FUEL PRSSURE 2 to 2.5 psi.


Weber Redline Carburetor Applications ca. 2002-2203

DCOE...Early style brass floats 8 to 8.5mm, at radius of float to lid with gasket. Late style plastic float 12.5 to 13mm at extreme tip of float. All setings are gasket to float.
2.5 to 3 psi.
For agressive off road use, float drop s/b limited to 1. to 1.5 mm.

[240260280]

Good questions young grasshopper!

 

You are correct.  In general,carbs work by venturi vacuum (often called depression) lifting fuel from the surface and pulling it into the throat.  In the DCOE, the idle circuit, progression circuit and the main circuit all do this.

 

The amount of fuel lifted is proportionate to the fuel level.  If it is too low, no fuel will be lifted. If it is too high 100% fuel will be pulled and no air (except what is coming down the throat).

 

Adjusting the fuel level in a DCOE is not a fun job but once it is done it rarely changes.

 

Here are two ways to do it, I recommend the second:

 

On car:

0. remove plugs

1. remove fuel lines to a carb

2. remove screws holding that carb's lid

3. lift lid and bend tab

4. siphon some fuel out of bowl to lower level

5. install lid (often two screws are fine)

6. connect fuel hoses

7. run starter to fill bowl

8. measure fuel level

9. if not at target (27mm) repeat 1 to 9

10. Repeat for all 3 carbs

 

Off car:

Get a friend, a ladder, hose, gasoline (water works but gas is more accurate), a clear plastic bowl, and an area with a high roof.

Do this: https://www.classiczcars.com/forums/topic/52084-setting-fuel-level-weber-dcoe/

 

Note: floating the bowl in gas will be more accurate for the level however the 8.5 to 9 foot head of water will give the right pressure on the valve, so gas in the bowl and water in the hose for best results.  I just used water and the result was all 3 carbs were the same level. When I put the carbs back on the car and ran the engine, they all measured the same level which I think was ~ my target.  Memory is not what it used to be.

If you use fuel in the hose, 10.5' of head will give 3.4psi at the carb's needle valve.

Edited June 5, 2018 by 240260280