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Pictures Added: Weber 38 DPS 100 - what is it?

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PICTURES ADDED - SEE BELOW

Hi all

Does anyone on the FAQ know the differences between the Weber 38 DG_S model and the Weber 38 DPS 100 model? What is the purpose of the additional vacuum operated throttle actuator? I can't find any amount of information anywhere on this model carb.

Thanks in advance!

Tom

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If you don't get an answer from anyone on this board you might try contacting Pierce Manifolds to see what they may know.

www.piercemanifolds.com

Bob Napier

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Thanks C.D. and Bob,

I very, much appreciate the quick responses. I had previous located the specs (jetting, venturi, pumps etc) but had not seen the nice diagram provided by C.D.. The DPS is not to be found there either that I can see. This thing looks just like a 38 DGMS, except for jetting and the additional vacuum throttle actuator which I assume under low rpm and sudden load like an A/C compressor kicking in would respond with a tug on the throttle.

It's NOS and from Bologna....I am going to re-jet it for the 2002 using the jetting starting point for my stock '76 with Tii exhaust manifold and give it a go. I will report my findings.

Best,

Tom

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Thanks Toby

Good info on Weber models.

I am attaching pictures to help with understanding what a 38 DPS 100 is. This is not progressive, but synchronous operation. I re-jetted the carb tonight as follows:

Mains 155 to 135 (will also try 140s)

A/C 155 to 175

Idles kept at 55 (will also try 50s)

E-tubes F80 to F50

It appeared to be setup for a larger engine displacement (quite rich). I'm all ears if anyone has a better jetting setup to recommend.

1. Bowl End

38bd79208a8f9c0d61063a38bf896c5f_zps121bcdba.jpg

2. Underside showing vacuum actuator for throttle

b3bf26a649fd25023c451a7bbb8b6ef9_zpscf4f7783.jpg

3. Top Left showing vacuum actuator. The adjusting screw meters the amount of vacuum needed to actuate the throttle actuator. I now believe that this works to kick open the throttles a bit, just enough to give fuel to overcome conditions where high manifold vacuum occurs i.e. on deceleration or say on low rpm loading (crawling along) to avoid stalling out.

04edfdd6f38366be87ce3473bfab97b4_zpsf330937d.jpg

4. Throttle rod end - also comes with a nice cover

59b9ced23d72f5a937c4c993ae1fc9d5_zps897b1c08.jpg

e12eecc85bb2520bb70774e60c13bfcd_zpsfd5d1a27.jpg

5. Manual choke setup

2715ed9ca58b0cefd2aaa832d2b7db97_zps16e1f075.jpg

6. And here is my '76 2002 that the carb is going in...so out comes the 32/36. C.D. eat your heart out...

18d24a45.jpg

Tom

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have you got a stock or modified engine? If it's stock and you have a 32/36 I suspect this will be a backward step in performance, driveability and economy. Bigger isn't always better and a 38/38 is only really going to benefit a well flowing head, high compression and a lumpy cam, IMO.

N

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Hey, thanks-

yup, that's synchronous. 'P' = Peugeot, then!

What I can't see is how the vacuum pull- up is decoupled from the

shaft- it has to be somehow, right, so that you can open the throttle

without having to move the vacuum diaphragm...

And I'll add a guess, having dealt with things like this, that it's either

for an accessory like air conditioning or an auto trans,

or if it was for an emissions country, that it added fuel to keep the

mixture from going too lean under certain circumstances, just like you mention.

neat. If it meters like a DGAS, then your initial jetting seems like a

good starting place.

t

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Thanks Toby, et.al. for the comments.

The actuator when activated only opens the throttle plates a slight amount, I guess enough to provide fuel to counter-act a sudden load. Take it off, and I suspect we have a 38/38 with a manual choke.

So...after a couple of hours of work on a Saturday morning, I guess we will know how well this thing works.

The '76 BMW is relatively stock, with the exception of a Tii exhaust manifold and exhaust system, stock intake with 32 mm ports bored out to 38 mm and ported to match the cylinder head. Emission equipment has be removed entirely. All cylinders have compression within spec, valves properly adjusted, timing perfectly set, etc. Many of the other 2002 drivers in the DFW area here that I run with are using 38/38s on relatively stock cars with very good results (performance and economy). Believe me, I certainly do not want to open the 32/36 versus 3/38 debate - there is already more than enough viewpoints written on the subject (in fact it was those views and comments which motivated me to try this bloody thing).

I will report on my findings!

Best - Tom

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Good luck Tom! Let us know how it works out. Do you have a AF meter? Will help a lot with tuning. They have a few styles. There is a clamp on that is easy to install with no welding.

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nice choice of wheels Tom

keep us posted with the jetting rezults.

(shorten that front bumper - please)

what's your VIN # _ _ _ _ _ _ _ ?

might have a treat for you

c.d.

my02overhead41704OriginalTeilebanne.jpg

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Hi C.D.

I always admired the Cromodoras - I found these last year and refurbished them. Campagnolo Electras would be mighty fine as well.

The VIN is 2373562. Built in 10 / 1975. Below is the original window sticker. I am the second owner. She is a real time machine. I have had her 8 years. When I was 16 this is the car and color scheme I wanted. It took me 3 other Bimmers and another 30 years to find her. We lived in Portland OR at the time when I made the deal.

I see you are have a soft spot for Anthrazitgrau Met as well. The dark wheels look awesome on your car. Regarding the bumper, I am not ready to shed 40 pounds off the front end just yet....

th_2a142eb1b4b753ca9fe2be24cb9ed039_zps5c5626c0.jpg

Best Tom

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Hey Nick,

I am going to check around the various speed shops in the area and see about renting a wideband O2 meter. Agree, the tool would save a lot of time and avoid potential engine damage. It took me a few weeks to dial in the 32/36.

Hope to see you at C&C this weekend.

Tom

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to Tom and VIN 2 3 7 3 5 6 2 :

Chassis Number 2373562

Model Year 1975

Motor Type M10

Platform.Engineering Series: 114

Production Date 1975/10

Retail Date 12/31/1975

Retail Center Roth BMW 211 NE Union Ave Portland, OR. 97212-3725

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