Hi folks, I'm in search of the Holy Grail of synced carbs. I have weber 40 idfs. All things being equal, air bypass screws closed, mixture screws backed out one turn after lightly seated, idle speed screw screwed in 1/2 turn after contact and linkage completely disconnected. Cylinders 1 and two read 5ish on my snail. Cylinders 3 and 4 read 10 on my snail. Which would be a more normal reading? Is this a carb issue or a engine issue. I'm confident I don't have vacuum leaks. Used new gaskets and hylomar blue gasket joining compound. Would a cylinder leak down test be in order? Thanks for any help.

Start by getting both sides of the engine to be roughly equal on the snail, with idle no higher than 1200rpm. Use the idle speed screws on the side of the carb. Open up 1/2 and close down 3/4.

I run Dellorto-40s on my 914 and used to have Weber-40s on the 356 I used to have. Both cars indicated around 4 on the snail at idle when everything was good.

Ansbacher

Never synch'd 4 cylinder Webers, but many many times with 6 cyl IDAs. About 4 on the synchrometer with small bore 6's. I do it the very old way learned from an old Weber manual... lost the hardcover book but author's name begins with a P!
Step 1 is disconnect L and R carb banks.
Screw in all idle air adjustment screws all the way in.
Run engine about 900 RPM
Get L and R banks close using idle adjustment screws
Do initial tune with idle mixture screws, enough to run all cylinders
Synch within each bank.
Start at the lowest synch reading cylinder and open idle air screw until match with highest synch reading cylinder.
Move to opposite bank and repeat.
Make sure idle stays sround 900 RPM
Adjust idle mixture screws
Adjust L to R throttle rods, leave one side loose, and attach both
That gets L to R close
Now, because of throttle linkage slop, you have to further adust the loose side running angine at about 2000 RPM.
Use synch to adjust and match both banks at 2000 RPM
Tighten everything down and rechech synch at both 900 and 2000 RPM

Idle air adjustment will likely remain the same for a while. The idle mixture screws will likely need readjusted after some running.

I adjust idle mixture by turning each clockwise until cylinder no longer fires.
Then open it up slowly until cylinder fires, then open up another half turn. If cylinder spits through that intake, open up idle adjustent screw slightly more.

When you are doing your adjusting make sure the engine is warm. Otherwise you will have an awesome idle while the car is sitting in your driveway after start up, and a 2000 rpm idle 15 minutes later when you come to the first stop sign.

Zach

dumbjim...

Find a copy of this book....it's the best on tuning weber carbs on vw/porsche aircooled engines.

Click to view attachment

Wow, I wish I lived in your area. My first stop sign is 300 feet down my road. Then another, and then the stop lights start

Ansbacher

Weber book by Passini is the best.

I exaggerate. But I do have a good 5+ mile warm up route that only has 2 stop signs and 200 feet of elevation gain over 1/4 mile.

And getting your base set cold isn't bad so long as you expect the atrocious idle after a warmup drive. Then once you are fully warm turn the idle back down, make sure you are sill balanced (you should be) and you are good to go.

Expect to have to dance on the throttle starting it and going through warmup once you have idle set at hot idle. If you are unfamiliar with this, its it's disconcerting the first time. But once you learn the dance, all is good. For me it was:
Pump. Pump. Pump. Foot in a bit. Crank crank crank fire.

One of the best parts of fuel injection is letting myself forget the cold start carb dance.

Zach

Sometimes its feels like having a 914 with Carb's is another level of NARP LOL
Glad we have Raby ,Chris and Eric for Team Carb

For the Weber Book you can check it out online for an hour at a time to read for free

Here at
https://archive.org/index.php


Or buy it online

73 911 S had carbs. The Doctor said take two carbs and drive it in the morning.