Webber 40IDA or 40IDT

[hienz]

I am looking around for Webber carburetors or PMO carburetors
I came across Webber 40IDA and 40IDT
What are the differences? I read some where on the internet that Webber 40IDA are not good at low rpm and low speed is that true?

[zedsn]

In my opinion the weber IDA are the ones to use if you wish to run weber carbs. PMO carbs are very nice as well if you don't care about originality. I have ran both IDA and PMO.

[1QuickS]

IDT or IDTP? There IS a difference.

IDTs were Webers for Euro 1968 911T and IDTPs were 1969 911T and 914/6. The IDT is exactly identical to IDA except first progression hole is 1.0 mm vs. 0.8mm for IDA.

IDTPs are fine on 2.0T engines but if you up the displacement or install a more aggressive cam then you will suffer some transition tuning issues.

Also: Weber, not Webber

[Trackrash]

The idle air bleed is 140 on the IDTP compared to 110 on the IDA, in addition to the difference in the progression drillings.

Not sure what you mean by not good at low speed. Webers can be made to run fine on any variety of 911 motors, as long as you are not concerned about getting the best possible fuel economy.

What motor will you be running them on? IDAs are better suited for higher strung motors, but either can be made to work.

[hienz]

Originally Posted by Trackrash

The idle air bleed is 140 on the IDTP compared to 110 on the IDA, in addition to the difference in the progression drillings.

Not sure what you mean by not good at low speed. Webers can be made to run fine on any variety of 911 motors, as long as you are not concerned about getting the best possible fuel economy.

What motor will you be running them on? IDAs are better suited for higher strung motors, but either can be made to work.

I am looking at 40ida for my stock 1975 911s street and maybe some PCA autoX . I read somewhere people have to modify third progression to have 911 idle smoothly

[Trackrash]

Progression circuits have no real effect on idling. Your distributor may have to be modified to better deal with the carbs at idle, but that is a matter for another discussion.

Remarkably, on the street when driving part throttle you will be using the progressive circuits. Even cruising on the freeway, believe it or not, webers aren't using the main circuits (on 911s). The Weber triples are unique, you cannot compare them to the other dual throat IDAs.

With a totally stock '75 you may not be gaining much with Webers over a well tuned CIS.

Webers will come alive with the proper piston, cam, and exhaust upgrades.

[juanbenae]

you don't say where you're from, but fuel quality & the seasonal additives in CA's urban areas plays havoc on my webers. a year & a half in on them I am recognizing patterns developing via an AF gauge.

there's something to be said about getting a new set PMO's somewhat set up for your car instead of a set of weber that you may need to spend a few $$ on in addition to the $2500 entry fee. things like throttle shafts & other rebuild wear/maintenance items can be present in a older set of carbs. additionally set up may require multiple jet packages... more $$


lastly, forget the naysayers! carbs will wake up even a stock CIS motor nicely if you get the dizzy recurved and early or SSI exhaust. plus, they sound & look cool..

[Trackrash]

juanbenae

All good points. Especially the recurve and exhaust backdate.

I am guessing the OP is not in Kalifornia, as '75s are still being smog tested here.

[Jack Stands]

Read the excellent information on Paul Abbot’s Performance Oriented website. He’s done a wonderful job of explaining the nuances of these carbs.

[juanbenae]

Originally Posted by Trackrash

juanbenae

All good points. Especially the recurve and exhaust backdate.

I am guessing the OP is not in Kalifornia, as '75s are still being smog tested here.

nope, 75 is the last year of smog exemption currently in CA. see my sig. 76 & on get the call every two years.

[hienz]

Yep! No smog for my 1975 here in California (that’s how we spell the name of our state) this why this year I am doing some engine modifications for my anemic and SOB 1975 911S