[GoinManta]

I just put up on Ebay the Weber 40DFAV I had on my Opel Mantas 2.0L. It ran really strong at highway speeds but my 2.0L had stock valves and couldn't flow enough to run this carb at low speeds. Anyone with a 2.0L or 2.2L running a 38DGAS can run this carb. It is basically a 38DGAS with 6% larger venturis. Its rated for 325 CFM, a big jump over the 32/36 and a good bit better than the 38DGAS.

This is Webers largest downdraft, and hasn't been made in over 10 years. It was new when I put it on, and only has about 700 miles on it and is really really rare now.

Bidding starts at $250, a bit lower than what a new 32/36 goes for. No reserve.

Charles

 

[N61WP]

Charles,

what is the size of the venturis?

James

 

[GoinManta]

40mm and 40 mm, verse the 38/38 of the DGas.. maybe I got the nomenclature wrong.. If I do I am sure someone will correct me.

Charles

 

[N61WP]

No, not what I'm asking....the throttles bores are 38/38 and 40/40. The size of the venturis.....to measure them, look for the smallest restriction in the carb throat.
Jc

 

[baz]

i think a 38 dgas has 30mm chokes and a 40 dcoe has 32 mm so its a good chance a 40 dfav has 32mm chokes as well

 

[tekenaar]

i think a 38 dgas has 30mm chokes and a 40 dcoe has 32 mm so its a good chance a 40 dfav has 32mm chokes as well

BINGO! Base configurations in interchangeable AV (choke) carbs (DCOE/DCNF) are usually configured with 20% chokes, i.e. AV (choke) size = 80% of throttle bore size. I believe cast in chokes in 38DGxV and 40DFxV carbs follow this rule of thumb also.

Remember, venturi signal is what's used to establish the volume of gas sucked into carb throat by negative pressure (vacuum) created by this restriction. It's what makes any carburetor work. No pressure change (vacuum), no suction of gas . . . carb no work!

 

[GoinManta]

I will check.. don't have a micrometer to check with though.

 

[baz]

charles a ruler would do but if you open the throttle plates or choke plate weber are nice enough to cast the size in normally

 

[GoinManta]

Then it dawned on me... I have a Weber book..

The book notes some differences between the DGAS vs DFAV: (not sure what it all means, but here it is)

DGAS types are:

Fitted with a discharge blanking needle which determines the amount of fuel returned to the float.

Choke shaft is Steel

Have two Semi-floats

DFAVs are:

Choke shaft is brass

Has a large single float

Are provided with a float chamber vapor discharge valve which prevents the build up of vapor within the float chamber. The valve is open when the throttle valves are fully shut or fully open and additionally controls overfeed enrichment air bleed.

Equipped with an accelerator pump lever incorporating two pivot holes whereby the pump stroke can be varied.

>>>>>>>>>

Also found this online:

The DFV Series offers the same increased performance, economy, drivability and excellent values does the DGV Series. The basic design of the DFV carbs is that of the DGV Series. but as a mirror image, with the primary and secondary barrel position reversed in the body While the throttle lever in the DFV rotates in a clockwise motion it rotates counter clockwise in the DGV. The DFV also features a power valve circuit to facilitate low vacuum running conditions-perfect for long duration, high output situations. You get the same value, parts availability and durability as with the DGV in a carburetor suited for your needs.

>>>>>>>>>>>>>>>>

The number 28 is cast on the outside of the carb body near where each venturi would be on the inside. I couldn't find anything else. Not without tearing the carb apart.

I did find out that the 38 DGAS uses 27mm venturis, so I would assume from the 28 stamped on the side of the 40DFAV, that they are 28mm.

After reading the Weber manual, and some other things it looks as if my problem with the carb was definately lack of bigger valves. The 40DFAV requires more vaccum to run than does a 38DGAS.

Charles

 

[N61WP]

Thanks for checking, Charles. I can't believe that I never even thought to pull out my Weber book to look it up. Duhhhh.
James

 

[tekenaar]

DGxV/DFxV venturi sizing . . .

Hmmmmm . . . thanks for clearing that up, Charles. Weber synchronous downdrafts must use a 30% choke rule-of-thumb then, unlike their sidedraft counterparts which typically use 20%. Maybe that's because, due to their much more direct path to the valve in a typical one-throat-per-cylinder configuration, sidedrafts flow so much better and don't require as much restriction to get a strong main mixture signal from their venturis.

While on the subject of Weber downdrafts, the 32/36 types use cast-in 26mm (~20% choke) and 27mm (25% choke) venturis respectively. Guess differential flow requirements dictate those changes for their progressive carbs. Not really too surprising when you consider that these carbs run on the primary only at less than 67% throttle opening . . . i.e. most of the time in a street car engine.

 

[GoinManta]

I also noted in the book a carb I have never seen mentioned before. It may just be the best one for a slightly modified Opel motor.

A 34DGAS

I will be trying to find one of those bad boys..

Charles

 

[baz]

charles its a weber 742f 9510aa or 722f 9510 ca used on ford granada's and consul's with an "essex" v6 in 2.5 litre rare beasties when new as most folks got the 3 litre
specs with emission gear are shown without its 27 mm venturi's

should i start to look now or in the morning ?

 

[GoinManta]

While on the subject, called Gil on a semi-related subject and found out he came across two old 32/36 double pumpers... (basically a 32/36 with accelorator pumps on both side of the carb). The secondary accelorator pump is opposite the std one in the area on the 32/36 that looks like something is missing.

I bought one, it may need rebuilt but he does have one left.

Also those looking for a new Weber 32/36 or 38 DGES/DGAS Gil said he should have them in this summer.

In the meantime you can order them from http://www.JamEng.com he has remanufactured 32/36s in stock. They have a 1 year warranty and all ned bushings, and everything. He says the casings even look better than new ones. They look like they have been polished. They sell for $365.

I have ordered from JAM before, good outfit.

Charles