Weber Carb set up - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 25 (permalink) Old 06-12-2019, 07:01 AM
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Originally Posted by quadrifolio View Post
back to topic, my understanding is that with EmCon carbs you can not interchage E.Tubes like in the older ones, it doesnt work that way, like the tube has a lot more and bigger holes for the transition phase, older ones doesnt have this feature, stick with the original ones and play with the fuel and the air

That may be. But, we have no baseline yet.

My Spanish 40DCOE 151s use standard jets though.

E tubes, or anything else, is not relevant if the float levels are off, jets are mismatched or incorrect.......

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post #17 of 25 (permalink) Old 06-12-2019, 07:04 AM
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Now you have me thinking and doing some web research... and I have to share this YouTube - love the 'Good Old Boy' approach.

Did you weld up a fitting on your manifold/header for a wideband O2 sensor? Or was it already there?
Welded a bung in for the O2 sensor.
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post #18 of 25 (permalink) Old 06-12-2019, 07:09 AM Thread Starter
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Are you mentioning the holes in the tube, or the progression holes? F16 E tube original tube for DCOE 44/45 have very few holes, and tubes with lots of holes definitely don't work.

But I think slowcreek is right, I need to get out of the guess work, and find out where I'm rich/lean and rejet accordingly. BTW there is a very interesting explanation of how emulsion tubes are working by David Vizard:

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post #19 of 25 (permalink) Old 06-12-2019, 07:15 AM
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I'll be sure to watch that video later.

check your float levels first.

78 Spider, Webers, header, Shankle cams, bumperless, lowered, Konis
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post #20 of 25 (permalink) Old 06-12-2019, 07:36 AM Thread Starter
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I checked the float level, and jets are new, so it must be the wrong jets and tube. But as camshafts are new and so is the exhaust, I'm starting from scratch...
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post #21 of 25 (permalink) Old 06-12-2019, 07:46 AM
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Quote:
back to topic, my understanding is that with EmCon carbs you can not interchage E.Tubes like in the older ones, it doesnt work that way, like the tube has a lot more and bigger holes for the transition phase, older ones doesnt have this feature, stick with the original ones and play with the fuel and the air
Weber had many features for emissions carbs. Some carbs had all of the features but others only had a partial set.
These features include:

Feeding the progression circuit from the well rather than the float bowl.
These required different emulsion tubes, usually F34 or F41 which are interchangeable.
They also required type 2 idle jets, typicaly F21 or F17

4 or 5 small progression holes rather than 2 or 3 larger holes.

Idle mixture screws with a narrower taper, more than one design

Air balance screws around the throttle plates.

Larger auxillary venturis which extend the progression range and bring in the main jet at higher rpm.

Many emissions carbs required larger main jets than classic carbs with the same venturi size.

The carbs in question here are 40DCOE44/45. They have "classic" progression plumbing and use "classic" emulsion tubes and idle jets.

At part throttle up to about 3000 rpm, idle jets have the most influence.
At part throttle and higher rpm main jets have the most influence.
At WOT main jets and air correctors have the most influence.

Certain emulsion tubes work best with certain cars. 4 cylinder Alfas always had either F9 or F16 unless they were emissions carbs. I have experimented with F9 and F16 with data logging. F9's are marginal at high power and rpm and tend to run lean. To correct that you have to install bigger main jets and that makes the mid range too rich.

A float level that is too low will cause leanness, particularly in the transition phase. One that is too high will cause richness .
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Last edited by alfaparticle; 06-12-2019 at 07:57 AM.
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post #22 of 25 (permalink) Old 06-12-2019, 08:03 AM Thread Starter
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very interesting alfaparticle! so you would recommend F16 over F9, right? Thinking about float level, I did correct it in when changed the jets to early 2000 ones. DCOE 44/45 have 7mm, and CDOE 76/77 have 7.5mm. I'll try to put it back to 7mm and that should enrich the transition

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post #23 of 25 (permalink) Old 06-12-2019, 09:48 AM
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0.5 mm should not make much difference.

A friend - 65Sprint, asked me to drive his car and tell him what I thought about it. It had a flat spot around 4000 rpm. He thought that it was lean and he was using larger than normal main jets. I lent him my wideband AFR and he found that it was too rich. He was then able to eliminate the flat spot by installing smaller jets. Even experienced drivers can find it hard to distinguish between an overly rich and an overly lean condition.

What size venturis (chokes) are in your carbs?

Ed Prytherch
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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 #24 of 25 (permalink) Old 06-12-2019, 01:24 PM Thread Starter
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32mm (DCOE 44/45 is normally 30mm). And you’re right: I may be too rich as I went back to std set up (117 main jet, 180 air jets and F16 tube), and transition
was much better. I also checked the cams timing, and it seems my exhaust valves are opened 0.15mm too high at BDC. So I probably have a bit more valve overlap than it should. I’ll correct that tomorrow and see the effect. But in any case I think I now need a rolling road and check my air/fuel ratio to make sure my engine runs properly
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post #25 of 25 (permalink) Old 06-13-2019, 11:12 AM
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Quote:
Originally Posted by quadrifolio View Post
model 44/45 is an EmCon (Emision Control) carb idd for 1.6 so you have to stick with the original E. Tube otherwise they are never going to work properly. Normal DCOEs (No EmCon carb) use a total diferent E. Tubes, so the E. Tubes are not interchangable between EmCon carb and No EmCon carb (any number above DCOE32 is an EmCon carb)
Nearly right. 33's, 34's, 35's, 70/71's, 90/91's aren't true Emission Control carbs either.

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