We are converting a stock 2 liter 4 cyl from D jet to Webers. My gut is telling me a 40 IDF with 32mm venturis is the correct starting point. I am considering purchase of a complete set of 44 IDF's, but are unable to locate 32 mm venturis. Assuming 32MM venturis can be found are 44 IDF"s too large for a stock 2 liter?
thank you

40 IDFs are best, but 44s will work if you choke them down. I say 40s are best because they already come with 28 venturis. You may have a more difficult time dialing them in with 44s and bigger vents.

Question: is the diameter air the manifold interface different between the 2 ?

If the carb throat is larger than the manifold port size, a restriction is formed at that shoulder. Carb base diameter should match the manifold throat size.

930cabman...

what's wrong with the stock D-Jet?
have you tried to get it to work?

If converting a stock engine to carbs use 40IDFs since no change to cam.

Several years ago I came upon a low mileage rust free Alfa spider (flood car), after rebuilding pretty much the entire car, the D jet stumped me with it's sensors, ECU and a million electrical connections. I found a set of Weber40 DCOE's and never looked back. If/when a FI system is reasonably new and working I would service it, but working from a basket case, no way. Tooo many variables

At what what RPM is max HP? I'll take a swag at 5800. My Weber manual chart says 36mm venturi. A 36mm venturi is probably better with a 44IDF.

This is a stock 2 liter 4 cylinder engine. my gut is telling me probably 32mm venturis

My 5800 rpm swag was off. My 914 spec says max hp is at 4900 rpm. This'll decrease the main venturi size to about 32mm. So I would recommend 40IDF.

I forget how underpowered the T4 is!

I would run 44 Webers. Personally I run 45 dells on a 2.0 with a cam and headers and have no issues. Dells are much better.

Yes, with dished pistons/low compression it's near impossible yp make decent HP. If I live long enough and/or have some spare time I would like to try a twin turbo setup. I have not seen much on this board with this topic.

Yes, my gut is telling me twin 40IDF's with 32mm venturis will work well with a stock 2 liter. 500cc/cylinder volume

You want 40's. With that engine the vacuum signal in 44's is going to give you problems. It will probably run very well with 40's and 28mm chokes

OK so you have:
Stock 2.0L type 4 with stock FI cam and distributor.
And you have dual 40 IDF to install

This is what we used on a customer 914 rebuild in 2019
2.0 L
009 Dist new one
Web Cam... think it was an 86
Dual Weber 40 IDF
Vents 28
AC 200
EM F11
Main 115
ID 55

Ran fine....they wanted just a driver.

Maybe this will give you a start....GLW your project

CB Performance's Bob Tomlinson's' book shows:

AirCooled VW engines with Dual 40IDFs

1835-2000cc 28mm venturi 145 M /220 AC /F11 E /55 Id
2000-2234cc 28mm venturi 150 M /225 AC /F11 E /55 Id

What year Alfa?

The spiders never came with Djet actually
They were spica and then motronic DME

Your car would be worth learning d jet
They are a great and reliable system actually

Almost like they were made for the car....

1985 Alfa spider, maybe it was L jet, but very similar. ECU, sensors, many many connections. When operating correctly the Bosch system is far superior to any carb system, but with 50 years old stuff, it's another story

Just for the record. That's what everyone said in the late 80's too.

Not a carb hater by any stretch. Just think it's funny that the debate rages on 30 years later and I hear the same arguments out of both sides of the debate.

For me, it comes down to simple.

Bolt on carbs, add fuel and go.

50 years old FI stuff = headaches

Simplicity for me too. I worked with the black magic of the D-jet, but had more working knowledge of carbs. I had a harder time diagnosing an issue with the D-jet and started to take away things that could potentially cause issues, but were not needed i.e., Cold Start Valve, decel valve. Ultimately trying to get back to a simplistic system.

This does not mean that carbs are simple. They have their own set of rules you must follow and several have spent hours tuning them to the point where - well it gets me down the road. Suffering from poor mpg, bucking, overheating, just to name a few. Most of these stem from dirty carbs, incorrect jets, or linkage setup.

If you start with a good working set and know your engine you can follow the methodical steps to get everything dialed in. What really helps is knowing how everything works together. I learned a big part of this a few years back when trying to tune a set on a new top end 2056. Learning that one could drive around with the main stacks removed was an eye opener. That is how you can set the idle jet and know exactly when the tip in starts for the main so as to not have a flat spot. That combine with an AFR can really help you dial them in perfectly.

When I had my 2056 carbed I tried 44s and 40s.

The 44s had ALL the power in the top end. If I was racing, it would have been ideal. Car would hit readline and just KEEP GOING until I was floating valves. Not great for regular driving, but fun when I could open it up.

40s were a better mix, but did not have the same oomph that the 44s had. BUT I bet most of that was the defective gasket set I got that did not have all the jet holes punched and caused me to be fighting with the carbs so bad that I eventually went to EFI.

That said, Microsquirt EFI has been the best.

Zach

I hear guys talking about Microsquirt EFI, but I have no knowledge of this system, sounds complex (expensive)

I ran 40's on a "stock" 1.7 and the same 40's on a 2056. As mentioned, 44's would be better on a higher revving race motor / race cam or larger displacement motor.

For 90% of your driving throttle response matters more than max power, id look hard at the 40s.

I’d cooperatively disagree on the Bosch Spiders, reliable and well supported.

[/quote]
1985 Alfa spider, maybe it was L jet, but very similar. ECU, sensors, many many connections. When operating correctly the Bosch system is far superior to any carb system, but with 50 years old stuff, it's another story
[/quote]


Nope... was not L jet either... 20 years difference in technology
you took off motronic... same injection that every 914/6 owner wants on their 3.2/6

Especially if you are running stock compression and cam designed for FI.

A properly tuned D-Jet system works very well on a stock and even slightly modified engine as many have done. Think you'll find over time carbs will make a cool noise, but not really produce any additional power and reduce fuel economy.

I am on the side of Fuel Injection.

I have run both Carbs and FI on a variety of engines in 914s. I have had a L-Jet four, a D-Jet four, a Carbed four with both Dells and Webers, a Carbed six, a MFI six, and a Motronic six.

The carbed four was the worst of the bunch. I never could get the carbs to stay synced, I always had problems with hard starting and fuel smell issues. I also had issues with hydraulic lock when it rained. Picture me in a driving rainstorm in the parking lot at work trying to get my car started so I could drive home.

Putting the stock D-Jet back on that engine made all the problems go away.

The second worst was the MFI six. It was great when it was running right. Fantastic throttle response, great power and it SOUNDS great. But when it got off, it was a bitch to fix. Hours spent with the protractors, and a wrench to get each stack synced, then syncing the pump to them as a group. Even when it was right, cold starts were an excrsize in frustration. Ether in the air cleaner. Cough sputter die. Another shot of Ether, cough sputter.. start running on 4 cylinders. Keep it running until the other two finally start to fire. Wait 5 minutes for it to warm up before I could drive.


The best is by far the Motronic. Turn the key, it idles... rain, shine,cold or hot. Second best is the L-Jet. But it is the father of the Motronic. It has cold idle issues, but that can be overcome with a little heel/toe until it warms up a little.

The d-jet is better than carbs. Even the carbs on our factory six irritate me.

I would buy a Bowlsby harness and put the D-Jet back on the car. Better gas mileage, better performance, and less gas stink.

Just my $.02.

Clay

It's looking like D jet might be winning.

First, thanks to all for your insight(s). I am trying to get this project running for my wife, so from that perspective the D jet works. I have three ECU's, last I checked there was a shop in Florida who could diagnose/repair these, but I cannot locate them. Then injectors, probably wise to send them in for cleaning. Wiring harness, other sensors, ...
From a dollars/value point could the D jet be the smart play?

Thanks again

I committed to D jet, sending the ECU to Module Experts in FLA and speaking with an injector service in Houston. A new carb setup is in the $860. range. Looking like the D jet is the winner

Make sure to get a refurbished harness too. That will fix the majority of the D-Jet ills.

Clay

I think you made a good choice. I tore my engine down in pre-Internet days because the combination of flaky D-Jet and increasing volume of oil pouring out of the case. Back then, access to info on D-Jet was hard to find where I lived and carbs were cheap so I rebuilt the short block with a carb cam. Fast forward to this year when I finally buttoned up the long block. Now I have these carbs and I'm sure they will be fine, but if I knew then what I know now, I would have put a stock cam in, invested money on a new FI harness instead of carbs, and used the wealth of info now available to put the D-Jet back in.

Whom can cleanup the wiring harness?

The injectors will be going to InjectorRX in Houston. On first reaction twin Webers appeared more simple, but thanks to all responding the Bosch D jet wins.

@930cabman

Check reviews on Module Experts. I have no experience with them, never used them but when I visited the page, it doesn't seem to me that they specialize in vintage Porsche stuff. Likewise Google reviews aren't great . . . but obvioulsly on-line reviews can be garbage too.

I believe Jeff Bowlsby who is a regular on this site, has the OEM ECU tester. He can tell if unit is OK but I don't believe he offers repair. Jeff fabricates all 914 harness wiring for engine and ECU harness that you would need. I've purchased his ignition harness as well as his alternator harness. Both are nice kit. FI harness is next up for me.

https://bowlsby.net/914/WiringHarnesses/#SpecializedEquip

You may want to consider Jeff unless you have a confirmation from Module Experts that they have the OEM ECU test equipment to test a vintage 914 ECU.

Don't quote me but I think Automobile Atlanta also can do ECU checkout if you're looking for a second source that is at least familiar with 914 ECU hardware.

I've gotten the impression from reading various threads on here that these ECUs rarely go bad.

That is true. However, they are 50 years old now. I'm planning to send the two I have to Jeff for checkout. The hope being that of the two I have, one is good and if both are, then I'll have a spare.

I really dislike troubleshooting with parts that you have no idea whether they are good or bad.

The main issue for me is that I'm buidling up my D-Jet as a MY73 system to match my car vintage which was a bit of an oddball system so 73' ECU's not as easy to come by.

Of course, eventually it will all go byebye for the /6 conversion.

Yes, I have gathered the same, these rarely fail, but my thought is to eliminate as many variables as possible. The Bosch system we are cobbling together is from several "baskets". I managed to clean up the case/trans today and couple them up, hook up a starter and try a compression check. 120 - 125 - 120 - 130 cold engine

Today was a good day in the shop, our new "rust free project" may be rolling down the road soon

Thanks to all for the input

I didn't read the whole thread, but my experience was that 44 Webers were too big for a 2.0L. My motor had Euro pistons, a sporty cam, ported heads, and headers. I was told 40's would've been better for that motor. Made nice power above 4000 RPM with the 44's though.

Agreed, from what I have determined the 40 with 28mm venturis is the right size for a stock motor. I have made the decision to go with stock FI