Just curious as to the application of each model of Weber... 40 44 &48idf and what are the differences between them?
What would work best with my old 1.8 with 96mm Piston and stock cam for street?
I am asking because according to the Weber website the"carburator cover" on my carbs would be from a 44 idf and my actual carb would be a 40. Is this good,bad or a non issue?

The number is the diameter of the throttle plate in mm. The overall bore of the carb is also a bit different. However, with replacable venturis (which the IDF has), you can neck a 44 down to the same venturi size as a 40.

For a stock-ish enigne, a 40 is plenty. You may want to go to a 44 for a big or wildly cammed engine. 48s are way too big for a street car.

I have no idea what the "carb cover" is supposed to be. The top mounting studs are, I believe, spaced exactly the same for the 40 and 44 carbs, so an air filter or linkage plate will both to either just fine.

From everything that I've read on this board about carbs, if you are keeping the stock cam, there is a consensus that you want to stay away from the carbs. Basically, you get reduced fuel economy and reduced driveability without any other gains.

That being said, I have a 2.0L w/performance cam and dual 44s. It doesn't like to be below 3k rpm, but sings from 3500 all the way to redline. Lots of fun for DE (and I imagine AX too once I get that chance) but it is..."difficult" to drive in stop and go traffic.

They don't like cold starts either....they kick, spit and yell until warm. Kinda like an old girlfriend I had....

QUOTE (mudfoot76 @ Jun 6 2005, 01:23 PM)

From everything that I've read on this board about carbs, if you are keeping the stock cam, there is a consensus that you want to stay away from the carbs. Basically, you get reduced fuel economy and reduced driveability without any other gains. That being said, I have a 2.0L w/performance cam and dual 44s. It doesn't like to be below 3k rpm, but sings from 3500 all the way to redline. Lots of fun for DE (and I imagine AX too once I get that chance) but it is..."difficult" to drive in stop and go traffic.

What venturis do you have in those carbs? Most people have carbs that are too big, and/or venturies that are way too big, which sounds like that's the case for you. Big venturies make the airflow move too slowly at low engine speeds, which makes the carbs function erratically. If you put in smaller vents, you'd find a big improvement in low-speed drivability, with some hit at the top end. Bigger throttle plates (40 v 44mm) also make small throttle openings more touchy. Turning a 44mm throttle plate 10 degrees opens more area than moving a 40mm plate 10 degrees, so the small throttle openings happen "faster" in carbs with bigger plates, which can make trying to drive slowly fairly difficult.

So, smaller carbs favor drivability, where bigger carbs favor power. On the street, drivability is usually way more important, so it's better to err on the small side with street carbs.

And yes, none of the dual Webers sold for flat four setups have any choke circuit, so cold-starts require some extra fiddling and the warm-up requires you to keep the throttle open for awhile to keep it from stalling. There ARE IDFs with chokes (actually enrichment circuits), but they require a custom cable and linkage arrangement to activate them. IDFs sold for use on FIAT twin-cam engines will have these circuits on them. The IDFs sold for VW/Porsche use, however, just have a blanking plate where the choke assembly goes.

QUOTE (mudfoot76 @ Jun 6 2005, 04:23 PM)

That being said, I have a 2.0L w/performance cam and dual 44s. It doesn't like to be below 3k rpm, but sings from 3500 all the way to redline. Lots of fun for DE (and I imagine AX too once I get that chance) but it is..."difficult" to drive in stop and go traffic.

I'm in the EXACT same boat. I've got the 40 tube things that I may put on to get it moving a little easier. I guess I just need to tweak it a little better or something.

I've got a book on Weber carbs that I need to read to see what I need to do.

By big cam you are talking .500 lift 290 duration. With port matching intake and exhaust.

Right now that's what my 2.0L has including Bus pistons (because that's just what it has). Long intake runners 46mm top opening, I think they 2" velocity stacks. 44IDF 36mm vents.

totally driveable on the street. Normally run it around 2500 RPM and when 3500 hits @ WOT you better be hanging on. As fas as top end.... IDONNO but it pulled hard to the rev limiter yesterday. So I took 5800 rotor out and my buddy flashed 6500 shift light top of 3rd gear.

If my 40 IDF's 32m vents make more power than that I will be doing a serious Happy dance. with a permanent grin to match.

By cover, the weber diagrams show it as the top plate of the unit.
I was concerned about the 96mm bore but if you all say no big deal I will beleive and tweek as I go.
This car will be lucky to be in stop ang go traffic maybe 10% of the time, so low rev performance shouldn't be an issue.
I appreciate the help as I wait for the "Weber book" to arrive.

These ar 48's. About the size of your head.

i've got the 40's. everything seems great except the cold mornings (most where i live!).
it will cough on the line unless you goose the throttle a bit, but then it's sweeeet on takeoff.

i'm really happy with them.

QUOTE (lapuwali @ Jun 6 2005, 04:58 PM)

What venturis do you have in those carbs?

I'll need to open up my files to see which vents and jets my mech and I finally settled on for all around use. A PO got the "hot" cam from FAT Performance, and I've got what looks like a plot of the cam lift profile too. But I need sleep now, so I'll look it up tomorrow and post it for you.