Weber IDA vs. IDTP / Different or Better?

vntgspd · 09-17-2006, 10:10 PM

Okay, I am in the process of rebuilding a set of carburetors and have two sets of cores to work with. I did a search and found a short thread on these two types of carbs but want to call on the experts here to confirm the difference.

My understanding is that the IDA and IDTP are virtually identical except for the mixture adjustment screws. My disassembly of the carbs and review of the parts seems to confirm this.

Can anyone out there confirm that this is the only difference. Also, is one considered better than the other for any reason such as tuneability?

Thanks!

David

Steve@Rennsport · 09-18-2006, 06:28 AM

Hi David:

Although you didn't mention the engine configuration of what you will be using these carbs on, either one works just fine in the majority of applications.

The IDTP is an emissions-version of the IDA for a leaner idle and off throttle response. In cases where longer duration (non-emissions) type cams are used, a lean spot can occur.

Hope this helps,

vntgspd · 09-18-2006, 07:03 AM

Thanks Steve!

I should be more specific:

Carbs are 40mm.

Engine is 2.4 "E" with 2.2S pistons. Stock heat exchangers and sport muffler.

So, based on what you are saying, if I am going to tune the car for performance driving (road, auto-x, track), then the IDA would be better, if there is even any difference at all.

Regards,

David

Steve@Rennsport · 09-18-2006, 07:17 AM

You're most welcome,....

All things being equal, I'd use the IDA's on an E-cammed engine for better idle and low RPM throttle response.

vntgspd · 09-18-2006, 12:49 PM

Sorry, just came up with another question:

One of the pairs I disassembled had additional copper washers under the needle valve. I believe this is was intended to act as a shim to effectively adjust float height rather than bending the "tab" on the float. Is this a correct assumption? If so, is this the preferred way for some reason or should I just stick to the original Weber method?

Thanks again for the input!

Steve@Rennsport · 09-18-2006, 02:22 PM

Quote:

Originally posted by vntgspd
Sorry, just came up with another question:

One of the pairs I disassembled had additional copper washers under the needle valve. I believe this is was intended to act as a shim to effectively adjust float height rather than bending the "tab" on the float. Is this a correct assumption? If so, is this the preferred way for some reason or should I just stick to the original Weber method?

Thanks again for the input!

You are right: one uses variable thickness washers to precisely set float levels (which are VERY critical on these carbs to run right). Its must be perfect for the screw adjustments and jetting to operate correctly.

Honestly, that works far better than pulling the darned things and tweaking the tabs.

Make sure you have 3.5 psi of fuel pressure before you start since the float level adjustments are predicated on that figure.

Shaun @ Tru6 · 07:20 AM

Reviving this thread with a question.

Long story short, I bought my 86 while looking for a 3.2 for my 73, couldn't pass up the good deal, but the car is too nice to rob the motor, etc.

Will most likely be selling the 86 to start the restoration, in earnest, on the 69.

We are thinking right now of rebuilding the 69S motor, plugging the MFI injector ports and putting carbs on it, making it plug and play for the 73. Entire MFI system needs to be completely rebuilt, scheduled next winter.

Will IDTPs work in this application or are they better suited for a milder motor?

Would Zeniths also work?

DaveE · 12-09-2010, 07:25 AM

Can an IDTP be modified to work more like and IDA or IDS carb?

Steve@Rennsport · 12-09-2010, 09:11 AM

Quote:

Originally Posted by DaveE

Can an IDTP be modified to work more like and IDA or IDS carb?

Technically, yes, but practically difficult.

IDTP's have relocated idle progression ports for emissions compliance and this becomes a factor when more aggressive cams are used. The idle mixture is calibrated much leaner so when "S" cams (or more) are installed, its quite challenging to get them to come off idle very smoothly.

For any performance application, I'd start with IDA's (or PMO's).

Shaun @ Tru6 · 12-09-2010, 09:23 AM

Thanks Steve, much appreciated.

Do you think Zeniths would work for my S motor?

Steve@Rennsport · 12-09-2010, 09:35 AM

Quote:

Originally Posted by Shaun 84 Targa

Do you think Zeniths would work for my S motor?

They "could" work, but far from ideal due to the operating RPM of an "S" cammed engine.

Shaun @ Tru6 · 12-09-2010, 09:40 AM

OK, thanks. Will start looking for IDAs. Really have some time before we'll need them. Heads won't even get sent to Anchor Atlantic until end of Jan.

Trackrash · Trackrash's Garage

It's not that hard to modify IDTPs. There was a thread on doing it recently. The main difference besides jetting, emulsions and venturi size is the idle air jet, which must be changed.
I also redrilled the progression holes on my carbs. Not sure if that was necessary.
You should get a copy of the factory manual that has the specs on all the old webers.

1QuickS · 12-10-2010, 04:27 PM

IDTP's have different progression circuit hole sizes and geometry as stated and idle air jets are 1.40mm vs. 1.10mm as used on IDAs. (The 46mm Webers used 0.80mm idle air screws.) I show pictures from my web site of the progression holes for IDTP and IDA, you can see the differences. In particular see that the IDA holes are placed higher in the port than the IDTP holes and increase in diameter from lowest to highest. IDTPs can have the progression enriched by drilling out the upper hole and by changing to a smaller idle air correction jet (I sell a modification kit for this purpose, the third picture shows this modification.)

IDA progression circuit holes

IDTP progression circuit holes

Tuneable idle air jets