The following only relates to Alfa owners who drive there cars on the street with 45DCOE 152 carbs.
Those of you who have purchased the 45 DCOE 152 carbs whether from Italy or Spain have surely noticed that the progression circuit is terrible when used on Alfa engines. The only way to get around the progression stumble of the 152's has been to fit an 55 to 65 F9 idle jet that is far too rich, thereby eliminating the stumble, but also getting a thick running bottom end and terrible low speed fuel consumption.
Ideally we would want to run the 55F8 idle jet which offers better fuel economy during the cruise mode and better low end transition.
Note: to those people who were at the latest dyno run, this modification was done 2 weeks after that run.
Upon examining the problem with my new 152's, I realized that the real progression culprit is the relationship between the "throttle plate" (closed) location and the progression circuit holes. The throttle plate should be DIRECTLY!! under the first (Largest) progression hole, completely covering it (very important) yet exposing it progressively at the same instant the plate is moved. If you examine your 45DCOE152 carbs, you will see this is not the case. The throttle plates are quite a ways back from the first progression hole. This traditional feature was changed by Weber when it re-designed the 45 series in the 1990's
. I have researched this and have found various reasons stated, none of which makes much sense.
I modified my carbs using the 2nd method, and it made all the difference in driveability and gas consumption (+20% in my city driving).
There are two ways to modify your carbs to work.
#1 Have special throttle plates made by Kinsler Fuel Injection. the plates will need to be made at the different angle of 74 degrees instead of the traditional 78 degrees. The cost is approximately $30 per plate and after you receive them, you will need to have them surface ground to a thickness of .057" from the standard .062" that Kinsler uses. After all that, your golden, just remove your old ones and put the new ones in .
#2 Drill a fourth progression hole directly above the existing throttle plate location. This will need to be done by a COMPETENT machinist !!!! Do not even think of doing this without a milling machine. I have done two sets of carbs (mine and a pair for a friend with a vintage racing BMW 2002). After carefull measuring, I determined that the critical dimension for the hole location was the same on my "Spain" carbs as my friends "Italy" carbs.
Note: your 152's may be different!!, measure them carefully or have them measured by a machinist.
The dimension determined for both sets (four different carbs) was the same at .710" or 18mm from the carburettor MOUNTING FLANGE SURFACE and .060" or 1.5mm offset (to the left for the left side and right for the right side) from the CENTER of the PROGRESSION CIRCUIT POT under the progression circuit cover. The new hole diameter should be the same as the largest (first) progression hole, which should be .048" or 1.2mm.
Note: If for some reason you are not happy with the modification, you can fill the new hole with a tiny dab of high quality epoxy after cleaning out any gasoline residue.
I just found this out two days ago, Weber has just recently introduced the 45DCOE 152G, and guess what the "G" stands for? .....ta daaa , four... yep count em..four progression holes!! They are also manufacturing the 45DCOE 9 again, which do work on an Alfa out of the box, however the throttle plate has a bevel on the inner surface and does not transition as well as the 4 hole progression circuit (I had a new set to try )
Note on the illustrations below, the Bic pen on white paper shows the progression pot as viewed from the top, left side is stock and right side is modified. The other illustration from a Weber tuning book has an added pen drawing of the stock 152 type carb for comparison to the other potential throttle plate problems. Note that example "A" is optimum.
Those of you who have purchased the 45 DCOE 152 carbs whether from Italy or Spain have surely noticed that the progression circuit is terrible when used on Alfa engines. The only way to get around the progression stumble of the 152's has been to fit an 55 to 65 F9 idle jet that is far too rich, thereby eliminating the stumble, but also getting a thick running bottom end and terrible low speed fuel consumption.
Ideally we would want to run the 55F8 idle jet which offers better fuel economy during the cruise mode and better low end transition.
Note: to those people who were at the latest dyno run, this modification was done 2 weeks after that run.
Upon examining the problem with my new 152's, I realized that the real progression culprit is the relationship between the "throttle plate" (closed) location and the progression circuit holes. The throttle plate should be DIRECTLY!! under the first (Largest) progression hole, completely covering it (very important) yet exposing it progressively at the same instant the plate is moved. If you examine your 45DCOE152 carbs, you will see this is not the case. The throttle plates are quite a ways back from the first progression hole. This traditional feature was changed by Weber when it re-designed the 45 series in the 1990's
. I have researched this and have found various reasons stated, none of which makes much sense.I modified my carbs using the 2nd method, and it made all the difference in driveability and gas consumption (+20% in my city driving).
There are two ways to modify your carbs to work.
#1 Have special throttle plates made by Kinsler Fuel Injection. the plates will need to be made at the different angle of 74 degrees instead of the traditional 78 degrees. The cost is approximately $30 per plate and after you receive them, you will need to have them surface ground to a thickness of .057" from the standard .062" that Kinsler uses. After all that, your golden, just remove your old ones and put the new ones in
.#2 Drill a fourth progression hole directly above the existing throttle plate location. This will need to be done by a COMPETENT machinist !!!! Do not even think of doing this without a milling machine. I have done two sets of carbs (mine and a pair for a friend with a vintage racing BMW 2002). After carefull measuring, I determined that the critical dimension for the hole location was the same on my "Spain" carbs as my friends "Italy" carbs.
Note: your 152's may be different!!, measure them carefully or have them measured by a machinist.
The dimension determined for both sets (four different carbs) was the same at .710" or 18mm from the carburettor MOUNTING FLANGE SURFACE and .060" or 1.5mm offset (to the left for the left side and right for the right side) from the CENTER of the PROGRESSION CIRCUIT POT under the progression circuit cover. The new hole diameter should be the same as the largest (first) progression hole, which should be .048" or 1.2mm.
Note: If for some reason you are not happy with the modification, you can fill the new hole with a tiny dab of high quality epoxy after cleaning out any gasoline residue.
I just found this out two days ago, Weber has just recently introduced the 45DCOE 152G, and guess what the "G" stands for? .....ta daaa
, four... yep count em..four progression holes!! They are also manufacturing the 45DCOE 9 again, which do work on an Alfa out of the box, however the throttle plate has a bevel on the inner surface and does not transition as well as the 4 hole progression circuit (I had a new set to try )Note on the illustrations below, the Bic pen on white paper shows the progression pot as viewed from the top, left side is stock and right side is modified. The other illustration from a Weber tuning book has an added pen drawing of the stock 152 type carb for comparison to the other potential throttle plate problems. Note that example "A" is optimum.
