Hello. I'm new to the forums here but have been reading and learning a lot. Thank you.

I have a pair of Weber 40s I plan to use on a 2056 I'm building. The carbs are used, and I don't know how they're jetted. Can anyone recommend a base line? I'm at an altitude of 486 feet. I appreciate any suggestions!

Steve

First question: What venturis does it have?
If you look down the barrel, you should see a number cast into the vent. It will be 28, 32, 34, etc.

Here is a jetting guide from the Weber Tech Manual that CB Performance used to provide with their carb kits. The copyright date is 1978 by Bob Tomlinson.

The chart above doesn't include the IDF.

My baseline Jetting Recommendation assuming 32-34 vents. Smaller vents will require smaller mains. Larger vents = larger mains and nightmare transition issues. May need to go larger on mains with ethanol fuels.

55 Idles
F7 ET (F11 will work but may have lean transition w/ 34 vents)
120 Mains
200 AC jets

If all else fails, you can email a guy called Bud Pauge who works for Redline Weber. He's a fountain of knowledge and has helped me out twice now - once with 40DCOEs and just this week with jetting my 40IDAs. He was very quick to point out modern gas runs a lot leaner, so the older charts may not be give the best possible results.

budp@worldpac.com

This is a great help fellas! I really appreciate it.

From my notes Dell 36's (flow similar to Weber 40's) YMMV

Carb Setup http://www.thesamba.com/vw/forum/viewtopic.php?t=572107 Carb Jetting http://www.aircooled.net/vw-carburetors-jetting-102/

a. Venturi/Choke = 30
b. Main Gas Jets = 130
c. Main Air/Correction = 180
d. Emulsion = 9164.2
e. Idle Jets = 60
f. Acc/Pump Jets = 50 (55)
g. Fuel Mixture/Idle Mixture Screws – 3.5 turns out
h. Idle speed 900-1100 RPM

I have a set of IDF 36s with 32 venturis

It has 47 idles, and 145 mains with 220 AC,

It pops a lot, especially when cold on decel, and the transition isn't too smooth. Should I bump up the jet sizes a little ?

' 74 2.0 unknown cam—i assume stock.

TIA

-Andrew

Look for manifold leaks

X2 on that ,many of the manifold kits come with thick paper gaskets that settle after time and leak,I would increase the idle jets to #55 seems to be the sweet spot for Webers,Dellorto's and the Zeniths used on the 911.
If your transition is still poor try dropping your mains down after going to the bigger idles,those mains you are using are a bit "fat" ,I would think 130-135 would be better with the vents you have,good luck.

145 isn't out of the ballpark if he's using an ethanol blended fuel. The 220 AC jet will also lead to a leaner mixture at higher velocities. 200 is base with with less than leading to enrichment and greater than leaning the mixture.

X3 on checking for vacuum leaks and increasing idles.

You also didn't state if it was exhaust or carb pops. Also check for exhaust leaks if exhaust pop.

Thx for all the replies
I get both.
Exhaust popping on decell when cold.
carb pops on initial start up and randomly every minute or two when warm and cruising.
I have no velocity stacks, could that help?

No idea what my gas has in it out here in Southern CA

-Andrew

You'll know if it has ethanol in it. There'll be a sticker on the pump that says something like "up to 10% Ethanol added".

Carb pops are usually caused by a lean condition. That means vacuum leak, clogged jets or jets too small. They can even be caused by an improper linkage or bad linkage setup (not synced).

Assuming you have mixture screws properly adjusted
1- check for vacuum leaks
2- check out linkage
3- clean idle jets
4- step up idle jets (as said, 47's are on the small side)

Exhaust pops have a few causes.

Again assuming mixture screws properly adjusted
1- check for exhaust leaks
2- adjust valves
3- idle jet too small

Great! Sorry for the thread hijack, I saw this thread and had to ask.
You guys gave me great notes on this. As soon as I finish my longs and floorpans and the car is back on the ground Ill get on this. In the meantime Ill order some bigger jets so I'm ready to go, maybe just replace the gaskets while I'm at it.
Carbs were synced and idles set when I had it tuned up and valves adjusted a few months ago. It runs pretty well aside from the popping, i have experienced partially clogged jets before and its not that bad.
Is there a best place to order jets?

It's been awhile since I've ordered jets. I had good experience with Redline and Paragon. I just looked at paragons website and I don't see weber jets there anymore. There are other places that some may know of that will exchange jets with you until you get the correct size.

I like Pierce for Weber parts and advice Pierce

I have used this place recently with good service:

https://www.partsklassik.com/c-24-weber-idf-carburetor.aspx

And I use Pierce manifolds and redline weber.

DONT use webercarbsdirect unless you have no choice.
They are NOT the "real weber" company, they are a chinese knockoff.

Just Google "webercarbsdirect " and you will find a lot of complaints.

Thanks for this one. It looks like Pierce has some amazing prices. I've never seen an ET for $10 and thats going back 20 years. How's their customer service? If it's good I'll put them on my list for Weber parts.

Aircooled.net is a great source for Weber parts also. I have bought my Resources he Weber's from them along with all the little parts. Check it out

I met them at Rennsport '15 and bought a few small parts at the show. I have not ordered online from them but the guys I talked to (I think one guy and his wife working the show were the owners) were very knowledgeable and friendly.