IDA emulsion tubes, How are they marked? Options

[Gary]

Hey 914-6 gurus,

Got the 914 last week after 5+ years of slumber at Aircooled racing. Picked her up in PA and trailered her back to Socal. First big storm chased me east, and coming back I beat the big storm of last week by about 5 days. Trying to dial in the carbs. Motor's a 2.7L built according to BA's book with MFI heads, E cams, RS P/C's. Have found the idles and mains too small (55 and 130). Going to order 60's and 155's. Air corrections are 180, which is correct. I pulled the emulsion tubes, but they aren't labled in any way I can tell. I want F3's. Can you guy help me with how to ID the size of my e-tubes?

Oh, I know, pictures - they'll be coming once she's roadworthy. Need to bleed the brakes and get the lights all working. Last update was here: Gary's car.

[Carl]

QUOTE (campbellcj @ Dec 10 2005, 02:06 PM)

Sorry for the mini-hijack but I currently have F26's as well and am wondering if switching to F3's might help smooth out the midrange? Mine is a 2.2S-spec and IIRC the 2.0S carbed engines typically used the F3's, but I didn't set up these carbs originally and am unsure if the F26's were deliberately chosen or just "happened". In other words, what is the functional difference between these emulsion tubes?

My understanding is the same and Rich's. Emulsion tube design was a trial and error process and the number means nothing except to identify the tube in the process of experimentation.

Reading I've done indicates that F3, F11 and F26 are the most common E-tubes in 914/6's, at least in the 2 litre cars. I don't know which tubes were used in the larger carbed engines. There are surely experts in the club that know about this.

The function of the tubes is to slow the gas delivery by mixing air into the gas flow as engine speed increases. Simply using the increased airflow to draw more gas into the airstream results in rich mixtures. Weber addressed the problem by using the E-tubes to slow the increase in gas flow by bleeding air into the stream. The placement and size of the holes does tie to mid and high speed performance and engine smoothness.

I once found an article about this on a VW web site (below) that was very good even though the examples don't apply to 914's.