OK,

So I've been amusing myself working out choke and jet sizes
and blueprinting a pair of Weber IDFs....

I'm wondering why the manifolds for these don't come with
equalisation slots cut
across the bottom of the manifold between the intake throats?

Obviously people all over the world are running them quite happily without equalisation slots..

But according to carb/volumetric balancing theory the idea is to get both barrels (indeed all four barrels)
flowing at the same rate (cfm). Now
you can stick on yer air flow meter (balancing device) and
adjust the carbs so they're flowing more-or-less the same...

But with the weber there's only one screw that adjusts flow for both barrels on that side....so if they are slightly out
there's nothing you can really do and this is where milling
an equalisation slot across the bottom of the manifold
between the barrels pays off and should really smooth things out?

So why isn't it commonly done? I guess I'm saying I think an equalisation slot is a *good* idea
but once done is a hassle to go back if there's some possibly bad effect I haven't
thought of........

??????????????????

RobK

[Edited on 5-12-2004 by splitbusaustralia]

just do it rob if it fails u will be able to fix it!!
cheers
rhys

What about the Air By-Pass Screw isnt that for ultra fine balancing but your not supposed to fool with it OR SO IVE HEARD :kiss

Set the air by pass to "off" and set your carbs.
IF you are sucking different amounts from the barrels, fine tune with the air by pass.

This is more to do with the butterfly shaft being bent etc

There was another reason why you dont have the balance. I will try and find it.

In theroy all the suctions for each cylinder should be the same, but theroy never works. Each cylinder chamber, compression ratio, may vary slightly etc etc

The webbers and or dells are mainly designed for racing and to be used under full power but this wont work on the daily driven street.

It wont hurt to add a slot between each manifold and a balance line between each side manifold. This would be similar to a Type 3 set up use some 5/16 tube.

This will smooth out all pulsations and make yr tuning easier.

i got twin webers on my bug and disconnected the choke and take it to a dyna tune place every time she needs a service and she doesnt miss a beat costs $90 to dyna it

If this would work then Weber would have done this years ago. These are "Independent Runner" (IR) type carbs. They are designed to run indendently of each other, each throat that is. What you suggesting is the same as having a vacuum leak between two ports and then trying to tune it, not much fun.
What you are suggesting will work on plenum type carb setups such as type 3 or twin Kadrons and the like, but the difference is one throat is feeding 2 ports which makes all the difference.
Not trying to flame you, just trying to help.

Gees, don't worry about offending me - that's why I'm asking!

What's your view on a balance tube between left and right sides? No good for the same reason?

Rob

Ive had a balance port on the webber set up in had no probs.

And when Vintage fits to Kombi with a brake booster, they add a line for the vacuum take off.

Keep in mind that the IDF series carb has been used in production cars as standard fitment and these don't have balance slots or balance tubes between manifolds.
I personally think that if a balance slot was to work then it would be masking another problem like a twisted shaft or misaligned buterflies.
Blueprinting a set of IDF's before use is a good idea, one area to pay close attention to is the alignment of the butterflies in the throat as I've seen brand new ones way out of alignment.
If you really want to get tricky then make an airbox to link both carbs, done right this will improve performance and reduce intake noise.

Thanks

the jey term I was missing was the 'independent runner' or
'independent runner manifold'. Search on that and quite
a bit turns up - a lot of it related to muscle cars!

But what I've found so far in fact suggests that set up
properly' and synchronised they are in fact designed and setup
to be treated 'like four individual carbies'........

dave - what I've read so far does suggest no equalisation
or balance tubes or ports are required, so I'll weld up the
balance ports to begin...

(Although I'd still be interested to find something on the effect
of equalisation...)

????????

RobK

Rob

ring Boris up if you can catch him n have a talk.

Dave,

Those lovely aluminium manifolds I have do have balance ports (one each side). But they’re not all that well done – just drilled through and tapped for a couple of 1/2 inch BSP pipe fittings.
It’s all a bit floppy and unsatisfactory. So I’ll weld em up and try and get it all sweet as per the independent runner manifold theory…….

If I can’t I’ll then move to experimenting with balance/equalisation tubes but I’ll put proper threaded bosses into the manifolds. Can always put a plug in em them too if it doesn’t help or hinders…

RobK