Question about Weber choke tubes

[enigma57]

Anyone bought any new choke tubes for Weber carburettors lately? Reason I ask...... I need a size which is no longer stocked. So the fellow I ordered them from said he'd have some made.

The choke tubes arrived today. Checked them and they are OK as far as external dimensions, and choke size. However, they are not tapered downstream of the choke point to gradually transition (widen) and match the interiour throttle bore diameter of the carburettor body as are original Weber choke tubes. Rather, they maintain same choke diameter for entire interiour length of the choke tube except for what I would call a bevel at the very bottom.

Seems very odd to make them that way with no gradual, tapered transition. I have decided to see if a friend of mine has the proper fixture to set them up on his lathe and machine the taper downstream of the choke point, similar to original Weber choke tubes.

Am I being overly concerned here?

Your thoughts?

Harry

[DrillDawg]

I would check with some of the major VW guys, they knew who has what squirreled away and some of them have a ton of experience with webers.

[englertracing]

Should be tapered

[enigma57]

I would check with some of the major VW guys, they knew who has what squirreled away and some of them have a ton of experience with webers.

Will do, DrillDawg! I did contact the late Gene Berg's family a while back regarding Weber DCNF parts (In 1970, Gene made a 'Berg Special' setup for VW's using a pair of 42 DCNF carbs), however they have sold most of their inventory of DCNF parts and no longer have the parts I am looking for.

I am looking for (3) of the dual pivot point accelerator pump covers and matching arms just now to replace the single pivot point covers on my Weber DCNF carbs. These particular pump covers also came on the DCNVH and DCNVA variants which were fitted singly to Simcas, Talbots, Maserati BiTurbo, etc......



Best regards,

Harry

[enigma57]

Should be tapered

I agree, Aaron. The choke tubes seem fine otherwise, so I will see about having the taper machined downstream of the choke point as it should be. I'll give Jack Lawrence a call Monday. Jack's in his 80's now, but still does some work on such things in his basement machine shop.

Will let y'all know how it works out.

Best regards,

Harry

[DrillDawg]

Gene Berg Enterprise was just who I was thinking about, he made a nice thick set of manifolds.

[enigma57]

Gene Berg Enterprise was just who I was thinking about, he made a nice thick set of manifolds.

I agree. Gene made some good stuff......

http://www.geneberg.com/cat.php?name=42 ... cPath=2867

I had a set of Berg DCNF intake manifolds for VW some years back and as you say, they were thick and well made. Reason I am looking for the dual pivot point style pump covers (these have a different fulcrum point location than the single pivot point style covers)......

I have done some preliminary testing setting up a single 42 DCNF carb on plenum style intake (1700cc engine) and this style cover allows use of #8 or #42 pump cams. Regarding pump shot...... These style pump covers along with #42 pump cams and #70 pump jets are spot on. With the single pivot point pump covers though, you are pretty much limited to the thicker #11 pump cams as used on most IR setups running DCNF carbs.

Best regards,

Harry

[Caprimaniac]

Agree on the taper. Lathe best way to do it.
I did a set with drill and flying/ propeller abrassive.

There is some good companies in the UK doing parts and rebuilt vintage carbs.
Do not recall their name. Dellorto- something?

The US companies doing webers like carbs unlimited, red webers.... again the names I do not recall, used to have lots of parts stocked. But for your 42’s- maybe not that straight forward.

[DrillDawg]

Heads up and Fat performance are two more that come to mind after looking in an old address book (97), lol.

[naukkis79]

Dellorto DHLA and later type Weber DCOE have auxiliary venturi and main venturi separate parts. Auxiliary venturi need to be combined with main venturi(which are available in different sizes) to have smooth transition to throttle area.

[modok]

when I bore venturis I use a 5-7 degree taper on the exit. perhaps 4, if that works, but no less. if it needs less I would bore the venturi straight ID up to where I could use a 5 degree

Entry is more application specific but two or three angles, perhaps 12 and 25.

the top and lower angles are used to narrow the smallest point to be the right width and location, a lot like a valve seat.

Some aftermarket venturis are not made correctly, so as a precaution I have purchased a size or two smaller and finished them myself.

For odd parts try "alfa1750" on ebay

[enigma57]

Thanks, guys! Appreciate the info!

The Weber DCNF choke tubes and auxiliary venturii are separate parts......





If Jack isn't set up to machine taper in choke tubes downstream of choke point, will contact Fat Performance in Orange, Calif. May also try Berg. They used to have a machinist there who would bore Weber 48 IDA throttle bores out to 51.5mm. Pretty sure he's retired now, though.

Have located a good source for DCNF parts in the UK. He does not have the pump covers, though. Have a friend in UK who knows a fellow there who has some used DCNVH carbs with the pump covers I am looking for, but so far have not been able to come to terms (I offered him what I felt was a reasonable value for the (3) pump covers in addition to sending him (3) single pivot point covers so his carbs would remain complete).

Will see if Alfa1750 on E-bay (Italy) has the dual pivot point type accelerator pump covers and matched arms for DCNF and DCNVH/DCNVA variants.

Thanks to all,

Harry

[Geoff2]

You could try Top End Performance in Hollywood, CA.

Bear in mind that if you are hogging out the chokes, there may be very little wall thickness left to get a decent taper.

[enigma57]

Thanks, Geoff! I've bought new carburettors and jets from Top End Performance some years back. Good quality, reasonable price in those days. Likely still so from looking at their online listings.

I had a phone chat with Jack Lawrence this morning. Always enjoy speaking with him. Jack still has his fixtures for reworking DCNF choke tubes on his lathe and after I described what needed to be done in order to complete the machining, blending and polishing, he said he could take care of it. So Ive boxed up my new (and in my opinion, unfinished) choke tubes and will take them down to the post office and send them to Jack for finishing.

It wasn't an issue of increasing choke size as you might run into with an IR setup. In reconfiguring these carburettors to function on plenum type intake, you must go smaller on choke size and increase jet size and pump shot. I have 34mm and 36mm choke tubes here for the 42 DCNF carbs and the 36mm choke tubes are pretty thin, as the outer diameter of both 40 and 42 DCNF choke tubes is 40mm. In fact, you can use 40 DCNF choke tubes in a 42 DCNF carb body if you shorten the bottom of them a bit (40 DCNF choke tubes are same OD as 42 DCNF, but longer). Conversely, 36 DCNF and 44 DCNF choke tubes will only fit their own respective size carburettor.

Best regards,

Harry

[enigma57]

Well, at times its a matter of 3 steps forward, 2 steps back......

The good news...... Jack Lawrence said he will be happy to finish machining and blending the unfinished Weber 42 DCNF choke tubes I got from Europe a couple weeks ago.

The bad news...... I mailed them to Jack and the postal folks have managed to lose them in the mail somewhere around Jamestown, New York according to USPS tracking. Still hoping they are not lost forever and can be found.

I have been in contact with alfa1750 in Italy regarding the dual pivot point style of pump covers. He sent me a note this evening to say he is unable to source them. I am still negotiating with a fellow in the UK who has some of these pump covers on used 36 DCNVH carbs, though. Still working at coming to terms.

Plan B....... If I cannot locate (3) of the dual pivot point style pump covers in question, will see if I can locate at least (1) of these covers with its matching arm. Will install it on one of my carbs along with a #42 pump cam and measure depth of diaphragm membrane depression at WOT. Will then duplicate this procedure using one of the single pivot point pump covers and thicker #11 pump cams I have here. Will then begin milling small increments off the thicker #11 pump cam until I have same depth of diaphragm membrane depression at WOT as with the dual pivot point cover and #42 pump cam. This will involve quite a bit of trial and error, as the actuating arms used with each style of pump cover use different pivot (fulcrum) points, so altering total depth of depression is not as simple as milling a #11 pump cam down to the thickness of a #42 pump cam.

'The difficult is what takes a little time. The impossible is what takes a little longer.'
Fridtjof Nansen, Norwegian explorer

Best regards to all,

Harry