The car is 2.0 with a "slight trick cam", euro jugs, and stock exaust, you know the pickle shaped muffler. Most of my driving is in traffic. The folks at RedLine say 44 idf is right, Most others say 40. Who knows?

This information is according to Figure 3.4, on page 27 of Weber Carburettors, by John Passini.
For a 2.0 liter engine with peak output at 6000rpm the main venturi selection chart predicts the optimum size to be 37mm. There is no curve for a lower peak output engine, but by guesstimation I come up with less than 30mm for 5000rpm.
Since 40IDFs typically come with 28mm vents, they aren't too far off for a mild engine. You can easily swap out the vents for 30mm ones, which should be available.
What primary venturi size is standard for 44IDFs?

i have 44's on my 2.0 aetup just like yours (w/ a bursch) seems to run good. lots of torque.

I use 44 IDF with 36 Chokes 135 Main 185 Air 57.5 idle and I think they are F 12 Emulsions, I dont have my log book here to check. This is at Sea level. Steve

I switched from 44's to 40's. Mostly because it took some top end off the car when my son drove it. Just so happened the car ran smoother and accelerated lots quicker. HMM...

2.0L Euro pistons, cam is .500 lift 290 duration, port matched heads, SSI and Bursch exhaust. Car was 1950 lbs.

44's would rev and rev. 7K or so. 40's would run out of steam 5500 or so.

i don't get it: the 40's performed better overall, though they made power lower?

This is interesting. Would like to hear more.

I would get a set of 44idfs and run the smaller vents probably something in the 32 range. If you ever decide to build a monster motor you can have enough carb to feed it. you will need a bigger idle jet than what comes factory the 50 is not big enough. look for something like a 55-60. Run an F11 emulsion tube and put a little baffle in the bottom of the float bowl. Keeps the carb from sloshing fuel away from the bottom of the bowls.

I have 44s on my Fat Performance built 2.2 with 38 vents. It produced about 140hp on the dyno and runs great.
Cheers, Elliot

have a set of 40's on a 1.8l type 1. dynoed at 115hp, not to shabby in denver 5500ft approx. you can use the 40's all day long id think theyd be good. but if you are buying and dont have. go 44's might not be as smooth.

I went with 44s because I didn't want to have to buy new carbs again when I build the engine. When an electrical problem isn't plaguing me it runs great.

When we were playing with carbs on the 914, we bought what everyone at the time recommended.... the 40IDAs. We spent a lot of time trying to sort through all the published BS and find out what worked.

We found that with a barely beyond stock 2.0 (cam and euro pistons) that we could not get venturis large enough for the engine. We also found that the distributors available to run carbs (at least at the time) were junk. We couldn't seem to get one (009 or 050) that would stay set for very long. The bearings seemed to wear quickly allowing the rotor shaft to wobble (changing the dwell and timing).

We eventually took the original 28mm venturis to a machine shop and had them custom bore and taper the venturis to about 34mm. He did a good job and the car ran MUCH better after that. We set up the main jets, air corrector jets and idle jets the best we knew how and the last season with it that way, we were pretty much pleased with how it ran. That was until we ran up against a similarly set up car with a narrow body and factory D-Jetronic. That car would pull down the straights exactly the same as ours. We may have had some top end on it, but not much.

That was when I was convinced that the D-Jet 2.0 was really the way to go and I haven't looked back. The next season, we decided to go with a 3.2L Carrera engine and our carbs went into storage. The engine got a stock cam, new euro Pistons & Cylinders and a rebuilt D-Jet. The engine then ended up in my street 914 where it still is today....

Now you know where my engine came from....

[QUOTE]i don't get it: the 40's performed better overall, though they made power lower?
Well think air velocity off idle to 3K RPM where most driving is done. and then on the higher end restrictor plate. Car was still pretty scary fast in the twisty stuff.

I guess If I was running WOT on a track with RPMs never dropping below 3500 RPM the 44's would have been the ticket. off the top of my head can't remember what the vent sizes were.

I've got the same set-up as BrettW, it works great, 7k miles no problems, no re-tuning just set it and forget it. Like other folks are saying, the 44's allow for future mods without needing to replace the carbs.