Push hard and live
Join Date: Apr 2007
Location: Carson City, NV
Actually, I think working on a float chamber vent may be creating a new problem.
We can all agree that it is a common problem to have a dead spot when accelerating with Webers. What is the problem?
The reason to have the float vented into the same chamber as the air intake is so that there is no difference between the air pressure entering the carb and the pressure acting on top of the fuel in the float bowl. If the inlet pressure always matches the float bowl pressure, then the fuel flow into the carb throat through the auxiliary venturi will respond ONLY to the airspeed passing the orifice in the aux-venturi. To have a predictable and controlled flow, you want to have no other factors impacting the fuel flow. If the air pressure on top of the fuel in the float chamber is changing in comparison to the pressure entering the carb, you will get either more or less fuel entering the carb, and it will not be in response to the changing air flow rate going into the engine.
Optimally, if the air pressure in the plenum was to go down for any reason, you would want the air pressure above the fuel in the float chamber to go down in unison.
So - at some points in time, lots of people, including Alfa, have experimented with having the float pressure picked up somewhere other than next to the carb inlet. Did this solve the problem? Did it simply masquerade the problem by adding another variable? The wide variety of Emulsion tubes hints that the problem is a sticky one, with compromises remaining to this day.
I suggest that the problem may have been that the E-tubes simply weren't researched and developed to where they actually worked perfectly. This is Keith Franck's position. If an E-Tube is perfectly designed to match the fall-off of the idle circuit in balance with the onset of the main circuit, then one doesn't experience the power slump in the middle from a too rich (or too lean) mixture. If one has a perfect E-tube, venting the float bowl to anywhere other than the same source as the air inlet could introduce a differing float pressure with respect to the inlet pressure, complicating or even defeating the perfection of the ideal E-Tube.
Thus - I strongly encourage you to try the VF tubes before you move the float vent pickup away from the inlet plenum. Simply opening the top of the cap would remove the necessary connect between the float pressure and the inlet pressure.
I acknowledge that Keith's research is on going, and I have questions about some of his assumptions as well. The one thing I can't argue with is that his VF tube, by itself, has noticeably improved the performance of my 2300. I didn't have a noticeable power sag in the mid revs, but now that it's better, I realize I had one, just not the debilitating one we sometimes see on 2000s and 2600s.
Carson City, NV
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
59 102 Touring Roadster - restoration complete, enough Alfa for any rational man. Or irrational, for that matter
Oops. Add to the "present" list, 10204 01488, 2000 Touring Roadster project
Two 1946 Stampe SV4C (c/n 294 "Rocinante" - wife's favorite airplane. RIP), and c/n 235 "La Bon Temps Femme" (gone to a new home, but never forgotten)
Zlin 50LA (+9 -6 gees, titanium spar, 1200 lbs, 260HP rumored to now be in Brazil)
1946 Luscombe 8A
Starduster Too (recently spotted at the Nevada City, CA airport - over 20 years and an entire continent separating it from our stewardship in Binghamton, NY)
1955 Cessna 170B (wife taught me to fly tailwheel in this)
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
Newest in the fleet
1967 Piper Super Cub on Wipline amphibious floats (a true "all terrain vehicle")
2010 Triumph Thunderbird
You can snap roll an Alfa only one time...