This Thread is WORK IN PROGRESS

In other words it 'ent complete yet, but I'm adding more to it regularly.

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The Weber DMTR and DMTL

Weber downdraught carburettors are a great enhancement and improvement over the piebergs which are fitted as standard to most Mk2 1.3's. Providing a manual choke, they will not stall in the winter whilst you remain in the driver's seat yet helpless to stop it. Being easy peasy to service and well supported in comparison to a pierberg, it's gonna last longer than the 'ticking timebomb' the pierberg has come to be known by some. Weber carbs offer more power yet equal or better fuel economy to the pierberg, and are easier to maintain and good for learning more about how things like these work, and me writing this guide after no more than a year of using one before moving to Twin 40's, is kinda proof of that ease and confidence factor.

The Weber DMTR and DMTL are twin-choke downdraught carbs, like the pierberg. Downdraught meaning the direction of air through the carb in relation to the engine. Air travels DOWN the carb before entering the inlet manifold, you get it. The ultimate diameter and flow of the two barrels in either carb is greater than the pierberg, by which they offer a gain in potential horsepower too. The two, which are the most commonly used models, are very similar except for a few minor differences. Having owned only a DMTR, I cannot really point these differences out and put money on what I'm saying is 100% correct. However the biggest relevant difference is that a DMTL has a slightly larger choke diameter, meant for engines of a slightly higher capacity.

If performance is what you have in mind, a DMTL will offer more room for maximum gain if you have other mods aswell, because of the larger chokes. Other than that, the DMTR would be preferential for driveability and lowdown power, but it's probably such a slight difference that it's not worth mentioning too much.

Acquiring the Carb

The best place to look for a USED Weber DMTR or DMTL these days is on this forum in the for sale section. They don't crop up that often, but I'd prefer to get one off here than off ebay, even though looking back mine was from Ebay. If you do look for one, make sure the seller specifies that it was made for a Polo or Golf. Other models of these carbs exist for Nova's and Fiesta's etc, but unless you know what you're doing, stick with VW-specific ones.

For NEW Weber downdraughts, look on ebay, especially from the seller FASTROADCARS, which is a reliable and trusty shop run by a knowledgable bloke. Full blown kits exist on there 'what' would take 'alf the pain of getting the bits and bobs together 'what' you need. But they are a little expensive.

Anatomy of the Carb

So, got your new Weber Carburettor in front of you? I don't care, I'm gonna go on ahead anyway. The Carburettor used in these pictures is a 32/34 DMTR, not a DMTL.

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Looking at the 'front' of the carburettor;

Fuel Inlet - This is the fuel pipe union through which fuel enters the carburettor.

Fuel Outlet (Blocked Off) - This is the fuel pipe union through which excess fuel leaves the carburettor and drains back to the tank - or this is what I WOULD be saying if this particular carburettor did not have a bung in place of a union. This means that fuel has no circulation out of the carb and this will require a swirl pot to be added to the fuel system, which will be explained. If you DO have a union here, this means that fuel will exit as well as enter the carb, and you will not necessarily need a swirl pot. Why is it blocked off? God knows.

Vacuum Diaphragm - This is a unit which operates by vacuum, which is carried by the pipe which bends 180 from the body of the carb into the external 'saucer'. To be honest, I can't remember exactly what it does, but it'll do you no favours if it isn't working properly. You can do an easy little test to see if it is working properly, explained later.

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Looking at the 'offside' of the carburettor;

Throttle Cable Holster - This is the throttle cable bracket which I used for my setup. As some adaptor kits to fit weber carbs to standard inlet manifolds do NOT include a bracket to suit, I customised mine in a way which I'll show later.

Manual Choke Linkage - This is a lever which relies on a manual choke cable in order to operate. When the choke is pulled out, this level falls anti-clockwise which not only further closes the choke flap, but also slightly acts upon the 1st stage throttle butterfly by way of the 'cam' on the bottom edge of it, as you can kinda see in the picture.

Throttle Quadrant - Is attached to the 1st stage throttle spindle and is a pretty busy linkage component. This particular quadrant is once again a customised job by way of combining two throttle quadrants into one through some chopping and fitting, but more on that later. The nib on the end of the throttle cable hooks onto the right side, approaching from the left. The screw attached to the top is part of the choke mechanism. This is what contacts the choke cam on the choke linkage, and is adjustable for more or less act on the throttle when you use the choke. If that makes sense.

Airbox Vacuum Stub - This stub comes out from the front of the carb and hooks up to your hot/cold air selector - IF you use one. If you don't (when running a bolt on filter or aftermarket item), then this is blocked off. When connected, the carb will operate the hot/cold air selector to help prevent carb icing.

Vacuum Diaphragm - This is the rest of the vacuum unit mentioned at the front, as seen from the side. The vacuum operates a lever, that's about all I know about it to be honest.

if you need pictures of a DMTL for reference and my jetting information let me know. i'm pretty sure i have an installation manual for a DMTR at home which could be scanned.

If you want pictures of DHLA's in reference to DCOE's i can supply them.

And if I say something which is wholly inaccurate in this post, tell me.

And if I say something which is wholly inaccurate anywhere else, keep it to y'self :p

humm that carb looks familliar :p

Well i want to flaunt these guys anyhow...

A pair of DHLA's

Pair of sidedraught dellorto DHLAs. Not Webers. So that's what a dBilas manifold looks like... only two trumpets... interesting gaskets ... shouldn't there be rubber cups and washers, or spring thackeray washers to absorb vibrations and prevent fuel frothing and manifold cracking. Maybe that's just a scare story for cast manis.

Nice Weber thread so far, I can add some jetting experience for the DMTR when you get there.

Yep, that'd be good! It's been a good 4 or 5 months since I sold my carb and manifold onto PortsmouthBMX!

Pair of sidedraught dellorto DHLAs. Not Webers. So that's what a dBilas manifold looks like... only two trumpets... interesting gaskets ... shouldn't there be rubber cups and washers, or spring thackeray washers to absorb vibrations and prevent fuel frothing and manifold cracking. Maybe that's just a scare story for cast manis..

The pic was just for reference... not the complete set up ready to bolt on, as above pictures. There will be thackery washers, better misab plates and 4 longer trumpets.

i prob have some dellorto and weber pics plus some data kicking around, i'll get around to posting it soon

If you need some DMTL photos - I'm swapping out my carb for a better condition one this winter & can take pics of my setup for reference?

One of the common misconceptions with the polo 1.3 weber is that it's a 32/34. It's actually a 28/32. This refers to the size of the throttle plates of the first and second "stage" at the base of the carb, the bigger they are the more performance potential the carb has. The three most common plate coombinations are:

28/32 (1.3 golfs, polos, etc) Venturi sizes: 22/22 (standard pierburg is I believe 19/21)

32/34 (1.6 golfs, sciroccos, etc) Venturi sizes: 24/25

34/34 (1.8 golfs, sciroccos, etc although the 32/34 can also be fitted to these) Venturi sizes: 25/26

The Venturi Size is probably the most important thing to consider when choosing one of these. If you pick a carb with venturis too big for the engine, you won't get good fuel atomisation as the air speed through the venturi will be too low. This may manifest itself with a flat feel, particularly on the 2nd stage. Take for example the 32/34 above. It has 24/25mm venturis. The Standard Single barrel solex fitted to the early 1.3 60hp HH engine has a 24.5mm venturi and a 34mm throttle plate, so this carb is more-or less double the size, which in theory means it can flow enough air for double the horsepower. So if your car is only going to make 80 or so bhp, the 28/32 will probably be enough, The bigger carbs should be the reserve of 1.3GTs, 1.4 and 1.6 conversions. I tried the DMTL on mine and it was very flat on the 2nd stage no matter what changes I made to it.

(standard pierburg is I believe 19/21)

Nearly,

The 052 129 016F or B on the 55bhp@5400rpm from May 1983 are 19/23

The 030 129 016B or C on the 55bhp@5400rpm from July 1985 are 21/23

These have 24/28mm throttle plates

The 052 129 016E on the 75bhp@5800rpm from August 1982 are 22/26

These have 28/30mm throttle plates.

Source www.ruddies-berlin.de Pierburg search the GIFs for Lufttrichter.

Hi, This is what i have done to my MK2 will post info if needed.These next are after getting it from my freind who blocked the exhaust holes in the head, done with the possable return to stock..still need to change throttle as cable rubs on bonet and some times does not return to idle..second pic shows standard cable coming on top of carbs my idea was to use this with a rod down to linkage saving all that money for a throtle linkage.work in progres..

That looks like an awefully complex way to avoid the £60 for a side-entry throttle linkage!

Oh well!

Still, I'm jealous that your brake master cylinder is on the nearside! My brake cylinder has caused me no end of grief because of clearance.

Hi, The braket is due to manifold being cut to fit later mk2 and early mk3 cyl head. leaving me with two exhaust holes above manifold, this cut piece is used to apply cable to carb. Not having this ment cable braket but will change soon..

Twin Webers, very nice.

What about the oil breather pipe that normally goes to the air intake that'sat the corner of the left air filter.

Shouldn't that have a tiny breather filter, or go to a catch tank ?

I think K&N even sell a small adapter panel for their filters to take in such fumes.

Twin Webers, very nice.

What about the oil breather pipe that normally goes to the air intake that'sat the corner of the left air filter.

Shouldn't that have a tiny breather filter, or go to a catch tank ?

I think K&N even sell a small adapter panel for their filters to take in such fumes.

Hi, have asked father X-mas for catch tank but gues wife might buy one sooner!!!! dont like idea of sump fumes going to only one carb with possible affects on fueling so will put tank on bulk head soon....as for now pipe exits to wheel well.not good for braking though..

does the breather put out much anyway? i decided it was a bad idea sending fumes into the aircleaner so dericted out under the car , i dont seem to get and oil /sludge out of it so no need for a tank really

HI, wrong post to ask might be re-located. Dont realy know how much mine puts out but there was a clean area in my engine bay where i just had the pipe placed in corner. With all the oil mist keeping paint nice and shiny (THIS is also a fire hassard as mist has warm contaminated air and oil vapours) Not really a nice idea to have crank case fumes just going any where so will fit catch tank soon, am concerned to about the fact the pipe should be filltered to pass the road worthyness inspection when it needs one...may not be the same in u.k. You may not notice as much the gunk comming out becouse you have it under the car? a tank collects it till you empty it.

Oil Breathers do put out a fair bit of crap over time,

I fitted my tank right at the front offside of the engine bay, in between the chassis leg and the radiator. It just fits.

Hi, thats where i hopr to place mine in cool air flow and out of sight at a quick glance of engine bay.

hey dudes

my webber dmtr seems to be ideling unevenly :(

i have adjusted the idle mixsture skrew and managed to get it ticking over nicely but evry now and then it just gets a mindof its own sometimes stalling and somtimes ideling high :S

anyone know what this may be ??

I cannot think of why that may be - It's possible that there may be an air leak somewhere, perhaps between the carb and the manifold.

Because you've got my old carb/manifold/adaptor plate, I can say that if it is leaking, it's going to be between the manifold and the adaptor plate, not between the carb and the adaptor.

If the below does not do anything to help, you may have to remove the carb and manifold to replenish the seal between them. But before you commit to that, perhaps:

Take the jets out and check they're not blocked, then reset the idle mixture screw to a couple turns out from minimum, and see if it's still doing it.

Is it whilst warm or cold? or both?

just cold at the mo

ill have a look at it tomorow

cheers for that danny