Webber Transition Ports

tjyak50 · #1 (**permalink**) 08-03-2011, 10:32 PM

What I have is a 2.8L inline six with 10.3:1 CR, ported / polished head, Big Isky Cam, headers, Total Seal, Etc. Just a massaged NA weekend warrior.

All 3 carbs and 6 tubes are very well matched. Using a "snail gauge" they flow the same, all rebuilt by me (lovingly), idle mixture set well. Just the transition from idle to mains is ****ty.

The progression circuit doesn't kick in till too late due to the location the first hole. I thought I read that you guys with the Cobras had the same issue so this is why I am here bothing you V8 guys with my little inline 6.

However I think there is a lot we can teach each other about Webers from different motors.
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Name: Still done..jpg
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Gaz64 · #2 (**permalink**) 08-04-2011, 04:53 AM

Tom,

Adding a hole as in your pic becomes a new "1st hole" not a "4th hole".

The "3rd progression hole" added to IDAs (which only have 2 progression holes) is exposed last, hence "3rd hole".

With your triples, what size plumbing are you using for intercylinder balancing?

If each intake runner is connected together to gather vacuum for power brakes with hose too large, then each cylinder will breath through more than one barrel and the butterflies will be virtually shut to get a normal idle speed.
Ideally you want the first progression hole ready to be exposed as soon as the throttle comes off idle.

What speed does your engine run at, at this point in the throttle?

tjyak50 · #3 (**permalink**) 08-04-2011, 06:55 AM

These are pure Individual Throttle Bodies with no interconnect. No vacuum assist and no brake boost. There is no communication between barrels at all.

The picture you see that I posted with light shined in the hole is all dialed in at about 1000 rpm. If I setup the butterfly so that the 1st hole is immediately exposed with throttle movement I would be at 1800 rpm.

Indeed I am talking about a New 1st Hole. One positioned exactly over the B-fly so that any throttle movement exposes the new first hole to vacuum and fuel can flow.

With the progression ports as they were designed (and not designed for THIS motor I am sure) the b-fly has to open a relatively long way before the 1st hole is exposed.

They do have a "soft mount".

tjyak50 · #4 (**permalink**) 08-06-2011, 07:57 AM

Follow up.
Pulled the carbs and they went into the CNC Mill and we drilled a new 1st hole .030" further downstream (towards the engine).

This made a massive difference in the off-idle mixture.
I want to make one more jetting change and I think I will have a usable progression.

Your input was very helpful here, thanks.

Tj