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Posted by: tornik550 Jul 13 2016, 03:10 PM

I have a freshly built 2.7l with 9.5:1 compression pistons. I currently have zenith 40 tin carbs with 34mm venturi's. The engine runs very well however I stumbled upon a nice set of weber 40 IDA's. I am much more familiar with weber carbs so I purchased them.

What would a good starting point for the following be?

venturis
idle jets
main jets
emulsion tubes
air correction jets

Also, are weber idf jets and vents interchangable with 3BBL IDA's?


Thank you

Posted by: mskala Jul 13 2016, 03:40 PM

I won't speculate on your settings as I have a smaller motor, but all the
jets and emulsion tubes are different parts, not interchangeable with IDF.

Posted by: Perry Kiehl Clone Jul 13 2016, 05:11 PM

Jetting shouldn't be that different from the Zeniths.

I'd start with 34 venturis, 145-155 mains, 175 or 180 air corrector, 60 idles and F3 emulsion tubes.

Posted by: Luke M Jul 13 2016, 05:22 PM

Here's a good chart with some starting points then you will have to fine tune it.




Attached image(s)

Posted by: tornik550 Jul 13 2016, 06:24 PM

Next question- Where can I find 34mm venturis?

Posted by: Mark Henry Jul 13 2016, 06:58 PM

http://youroil.net/weber_carb_parts.html

Posted by: 6freak Jul 14 2016, 03:12 PM

says NLA mark??

Posted by: Mark Henry Jul 14 2016, 03:22 PM

Works for me...$105./set
http://youroil.net/venturi_s.html

I think you are looking at the velocity stacks, the horns on top of the carb. They are NLA


BTW I used them for jets, vents and best price I found for a complete carb gasket set (2 carbs, not just one) and it was all quality stuff.

Posted by: tornik550 Jul 14 2016, 03:47 PM

The vents are in stock. I ordered a set last night. I agree- it's the stacks that are nla.

Posted by: Mark Henry Jul 14 2016, 04:25 PM

The most valuable tool for jetting your carbs is a wideband O2 meter.

Posted by: JmuRiz Jul 14 2016, 05:43 PM

I plan on running an O2 sensor in mine too, gives full rev range info to help with setup.
Got a bung installed on my headers and everything.

Question: will just one sensor bung work, or does it need to be on each bank (I'd guess one is fine)

Posted by: GeorgeRud Jul 14 2016, 05:55 PM

I'd imagine a bung for each cylinder would be most accurate but probably overkill.
My 2.7 conversion has similar jets as the chart, but a bit fatter on idles and mains. We used a Dyno to do the final tuning setup, which also is a good idea to extract the most from your engine.

Posted by: Mark Henry Jul 14 2016, 06:21 PM

I'd just run one in the muffler, you could put a bung in each side and just swap them.
One per cylinder doesn't make much sense, are you going to jet one side different than the other?
Or the other extreme every cylinder has different jetting?

If you are getting this much variance then there's likely something mechanically wrong with your engine or at least your linkage.

BTW badly adjusted linkage is the first thing I look for with carb tuning issues.

Posted by: tornik550 Jul 14 2016, 06:49 PM

Does anyone know if Weber IDF velocity stacks will fit on Weber 40 ida3c?kr

Posted by: Mark Henry Jul 14 2016, 06:56 PM

Measure the ID and the hole spacing center to center.

Posted by: Perry Kiehl Clone Jul 14 2016, 09:37 PM

Mark speaks the truth on the O2 sensor. It makes dialing in mixture easy. You can do it with one in the muffler and still tell when you are adjusting any barrel. I've only had one car in here with the wide band O2 sensor (a big hot rod 4 that you know very well Tornik) and I was really impressed.

Posted by: Mark Henry Jul 15 2016, 12:18 PM

I have a good O2 meter and I put it on every car I tune.

Carb cars I install the O2 meter and with my kit of jet reamers I head out on a country drive. Since I'm almost always going up in size, due to a bigger engine, the reamers work good. I'll go along watching my meter, stop on a side road, pull the jets and ream them to the next size (or half size) pop them back in. Repeat as needed.
I'll have them dialed in in less than 10 miles.

I'll buy the venturis, emulsion tubes and air correction as needed, but I haven't bought idle and main jets in years.

Posted by: 6freak Jul 15 2016, 03:24 PM

Posted by: 6freak Jul 15 2016, 03:27 PM

SOB