Weber Jet Sizes?, Is there a "ballpark" starting point? Options

[Porsche Rescue]

Can someone tell me the proper jet/emulsion tube sizes for Weber 40's on a near stock 2.0 (has "carb" cam but don't know specs)? So far I have only checked the idle jets and they are 45's. The engine runs OK but I think it could be better. There is a bit of a stumble at slack throttle around 3000 rpm. I think that is about the point of transition from idle circuit to main circuit. Any suggestions out there?

[krk]

Jim,

I have zero experience w/webers on 4 cyl's. But I've got a bunch of books -- got a /6 and had to learn somehow!

But I can offer data from charts on "DCNF and IDF jetting for air cooled vw engines" courtesy of the Tomlinson book. (I have a couple of others I can look at as well)

For dual carbs, they have idles at .55 down the (displacement) line for both carbs.

venturi - 28mm, mains are 1.55 for 2L+, air at 2.00, E tube is F24 for DCNF and F11 for IDF. P-jet (needle valve I believe) at .50.

Happy to look at more if it would help.

kim.

[maf914]

Jim,

What is the venturi size? 28 or 32?

Mike

[Porsche Rescue]

28 mm venturis. Guess I better tell the whole story.
I decided to use the carbs which came with a broken 1.7 high compression race motor which came with my car, instead of the new, never used Webers which came with the fresh (19 year old) completely rebuilt 2.0 which is now in the car (confused?). I just looked at the new carbs. They have 36 mm venturis, 50 idle jets. Carbs on the car are 32 v's with 45 idle jets. Haven't yet looked at the other jets/tubes. Can't believe there can be that much difference in venturi size in 40 idf's used on 914 engines, 1.7 or 2.0. The throttle plates in the ones with the 36's look huge compared with the 28's. Car runs pretty well but maybe I shouldn't be using carbs from a 1.7 racer rather than the ones which came with my new 2.0. Tell me more!

[maf914]

On my 2.0L (mild cam, ported heads) with 40 IDFs I ran the following with good results, although a little rich. This is sometimes blamed on the 050 distributer I was using, but I can't say for sure.

Venturis 28, Mains 120, Air Corr 210, Idle 50, Emulsion F11

From the HP Books Weber Manual, for 2.0L 914, 40 IDFs with 32 Venturis, they recommend:

Venturis 32, Mains 125, Air Corr 180, Idle 50, Emulsion F16


Mike

[rhodyguy]

jim, this can be exhausting. go to www.germanlookfurums and/or www.shoptalkforums, type4rum. do a search for "weber jetting", there will be plently of info. look for replies from jake raby in particular. any more severe symtoms, sneezing (back through the carb at idle)? poping out the back on decel? examine the a/f mix screws and ensure that they haven't been ringed/ grooved do to heavy handed turn in. look locally, you may need to find a shop to determine the a/f mixture with a sniff test. sounds like you are pretty close. it aint f.i. don't you like the way they sound at full throttle? maf is right though, hows the timing at 3 grand. here comes the mallory. this is one reason the 009 and 050 are less than the prefered dist.

kevin

[Porsche Rescue]

I am using 050 distributor. From the looks of the exhaust pipe it is a bit rich. Some pop back on decel. Going to 50 idle jet would make things even richer, right? Better check the mains and tubes.
What is the deal with 36mm venturis? Are they totally wrong for a 2.0 type IV? Thinking about installing the new carbs just for fun.

[maf914]

I would bet that on a street stock 2.0L 36mm vents in a 40 IDF will not provide a very strong vacuum signal at low engine speeds which will probably make low speed and transitional running kind of rough. 40 IDF's come with 28mm vents which provide good low speed response. A lot of people (including Jake and John at aircooled.net) think 28's are too small and recommend 32's for more top end.

Mike

[HarveyH]

I have a 74 2056 with a Pertronix and Crane Hi-6 ignition and 40IDF's. I'm running 28 mm venturies, 0.45 Idle's, 120 Mains, 200 Air Correction's and F11 Emulsion Tubes. Remember, the idle jet also controls most of your low to mid range mixture. The mixture at static idle is adjusted by the mixture screws and almost any jet will give you an acceptable static idle. As you come off idle and run up to 2800-3000 RPM the idle jet feeds the transition circuit and this is where the jet size selection comes into play.
When I was first researching the car, I checked with several Weber parts houses, and they all said to get a multi-spark CD igintion before starting to adjust jet sizes.
Harvey