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| Introduction |
The following 2 barrel carburetors fit 4 and 6 cylinder cars. We find
these carburators appealing because of the following:
- Adaptability
- Simple to adjust& tune
- Good driveability
- Decent fuel milage
- Available with automatic chokes
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| 32/36 DGAV and 38 DGAS
Webers |
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Many 2002 owners who had become frustrated
with the stock 2 barrel Solex carburetor switched over to the progressive
Weber 32/36 DGAV. This carburetor offered a nice improvement without a
lot of cash outlay. A few BMW owners discovered the Weber 38 DGAS. This
carburetor represented a decent performance upgrade over a 32/36 DGAV
but it didn't work that great out of the box. People who have just bolted
the carburetor on complain of poor gas mileage and a lack of top end performance.
This carburetor was originally used on a 2800 cc European Ford Capri,
so the pilot and main jets were too rich (poor mileage) and the power
valve wouldn't kick in at high speeds (lack of top end). The carburetor
was a bit pricey; plus we charge more to modify the power valve and re-jet
the carb. By the time we bored out the manifold to 38 mm and included
an air filter, the bill was out of sight! |
The small brass tube just above the booster venturi
is used for discharging fuel into the carburator at high rpm. |
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| 40 DFAV Weber |
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The 40 DFAV Weber carburetor is the hottest
2 barrel carburetor that will bolt on to the stock BMW manifold. It offers
a big performance gain over a 32/36 DGAV or 38 DGAS with no appreciable
drop in fuel mileage and good drivability. The carburetor has more than
a 20% flow advantage over 32/36 DGAV (see carb comparison chart) and is
nicely sized for engines in the 2000 cc to 2500 cc range.
The carb has dual 40 mm throttle plates that rotate towards each other
by way of a gear tooth arrangement and bolt to a stock BMW 2 barrel manifold
but the manifold holes need to be opened up to 40 mm to accommodate the
larger carburetor. The air filter housing uses a 3 bolt pattern. |
| A simple yet very effective 40 DVAF
Weber
mounted on a 2500 HiFlo ST Sport Engine |
One feature that is quite unique to this carburetor is
the high speed enrichment circuit. Just above the booster Venturi of
the carburetor is a small discharge tube that flows fuel at high rpm
(when velocity is high) and operates independent of the main jet circuit.
This high speed circuit is commonly copied and built into the 32/36
Weber Carburetor when run on Formula Fords. This system gets rid of
the troublesome power enrichment valve. In general, the power enrichment
circuit used on the 40 DFAV carburetor is fool proof.
One of the key factors to the 40 DFAV's great level of performance,
economy and drivability can be found in the fact that the fuel and air
distribution in the intake manifold is very even. Since both barrels
of the carburetor operate at the same time, fuel and air being discharged
equally to all runners. On a 32/36 DGAV Weber, fuel and air both discharge
over the #2 and #3 runners. This makes an engine run somewhat lean on
the outside two cylinders (#1 and #4) because fuel particles will not
make the directional change to the back of the intake manifold as easily
as air. If you'll notice the stock 2 barrel Solex carburetor, fuel and
air cover the outside two runners (#1 and #4) because of this problem. |
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| In
conclusion |
To date (March, '91) we haven't put a pair of 40 DFAV
carburetors on a 6 cylinder engine and, for the most part, we've found
that the 32/36 DGAV carbs give satisfactory performance and good drivability.
On 4 cylinder BMW's, the 40 DFAV Weber offers a big performance gain
over a 32/36 DGAV or 38 DGAS with no appreciable drop in fuel mileage
and good drivability. This carburetor has more than a 20% flow advantage
over the 32/36 DGAV (see carb comparison graph) and is nicely sized
for engines in the 2000 cc to 2500 cc range. This price, about the same
as the 38 DGAS, includes a modified and re-jetted 40 DFAV Weber Carburetor,
base gaskets, insulator block, air filter and a bored out 40 mm manifold
on exchange.
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Flow Test of the Stock 2 Barrel Solex
Carburator vs. the Weber 2 Barrel Carburators. |
| "A
Bolt On that Really Performs" - Article contributed
by Hank Davis |
| As a 2002 owner, I have always tried to
get more power from that "Old Reliable" two liter motor. Back
in the mid seventies I installed a pair of 45 DCOE sidedraft Weber carbs
on my '74. The results were less than expected. The drivability was
unacceptable in cold weather.
In 1989 I purchased a '76 2002, restored the body and installed a 2200
ST motor from Metric Mechanic, and also installed a 32/36 Progressive
Downdraft Weber carb. The drivability was excellent in cold weather.
However, the engine's performance went flat at the mid to high RPMs.
I suspected it was the lack of a good carburetor system, but I was not
willing to endure the drivability problems associated with sidedraft
carburetors.
During another one of my projects (another good story) out in Kansas
City, Mo. working with Metric Mechanic, Jim Rowe introduced me to the
Weber 40 DFAV Carburetor. Jim was "aesthetic" with the results
of his testing but the damn thing looked like a 32/36 to me. I know
how Jim Rowe operates, if he can get one more CFM of flow - then he
is "aesthetic”!!! I did not show much interest until James
Fields, Metric Mechanic's service manager, in his unassuming manner
showed his enthusiasm.
To make a longer story shorter, I got the 40 DFAV Weber, took it back
to upstate New York, installed it on my '76 2002 and performed some
testing of my own. I selected as flat a section of road as I could find
that was not heavily traveled by the NYSP. I made five runs in both
directions in each gear (3rd and 4th gears). The objective was to time
the acceleration from 60 MPH to 80 MPH. The average of the ten runs
in each gear is as follows:
| Carburator |
Test |
Gear |
Time |
| 32/36 |
60-80 MPH |
3rd |
8.90 secs |
| 32/36 |
60-80 MPH |
4th |
9.75 secs |
| 40 DFAV |
60-80 MPH |
3rd |
7.25 secs |
| 40 DFAV |
60-80 MPH |
4th |
8.56 secs |
The 60 MPH to 80 times are very impressive and can be communicated well
in print, but the increase in low end torque and top end performance are
as impressive, but my measuring device is from "the seat of my pants"
and cannot be communicated the same way here.
I could use a lot of over used adjectives (killer, awesome, etc.) but
the bottom line is that this is a "BOLT ON" that really performs.
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