Weber 34 DMTR, DMTRA and DAT differences?

tomnj

tomnj

Old fogie stogie
Can someone breifly describe the differences between these carburetors? I know that the "A" in DMTRA stands for Aqua (water choke), but I would like to know what kind of choke the DTMR has (manual, I assume) and if it can be setup with an automatic (electric or non-electric) choke. Besides the choke, are they exactly the same? Is the DMTR a direct bolt-on for a 1979 1.5 Motor with no mods to the linkage?

And how about the DAT, it appears to be the same size, but the throttle linkage looks different than the DMTR.

DAT:

34DAT.jpg
 
Many different versions of each, but

In general:
DAT, DATR, DATRA: water choke (that's the first A). The 34 DATR went on Euro 1500 cars. The 34 DAT is very similar but lacking many of the emissions stuff. The 32 DATRA was stock on US-spec 75-78 1300s (that's the second A).

DMTR, DMTRA: Manual choke carbs (that's the M instead of A after the D). The 32 DMTRA was stock on US-spec '74 1300, the 32 DMTR was used on euro '74 cars as well as some Fiat 128 models. The 34 DMTR was never used on any X (Fiat had moved away from manual chokes before they started putting 34 carbs on the X), but it bolts up just fine and needs only maybe some tweaking of the throttle linkage to install.

They all have a lot in common: same manifold bolt pattern, same jet families, same general principles of operation, except for the choke they generally interchange pretty freely. The idle speed is set differently in the earliest DMTRs, the mixture adjust screw is in a different [place on the 34 series, but that's about it.

There are detailed parts diagrams online at www.artigue.com and at Pierce Manifold's web site. It's worth finding these and downloading them.
 
I have.....

....a 34 DATR (water choke) on my slightly-modded '77 X1/9 1300; and a 34 DMTR (manual choke) on my even less-modded '77 Lancia Beta HPE.

I've got to say that these carbs work really well. I haven't had any problems with them in the ~4 years I've owned these cars.

On the other hand, the 30 DICA carb on my 850 Spider.....
 
34 DAT

I have a 34 DAT that I bought new before I did my rebuild and have no complaints. It's at least a little boost over the 32 DATRA that was on it when I bought it.
 
As Eric says... and I know NOT all the codes... but...

The other big difference between the emissions carbs and the others was that it had a VACUUM operated secondary!

The secondary was stymied by the "3-way vacuum valve" that did not allow vacuum to the vacuum valve on the carb until coolant heated it up and opened the three ports. (The other two were for vacuum advance at the dizzy and the to operate the GULP valve or exhaust gas recirculating valve.)

This is THEORETICALLY all well and good as you would want your engine to be at temp before standing on it... but the small coolant ports often clogged and or the 3-way valve failed and I know I ran around for sometime with NO vacuum advance and NO carb secondary for some time.

Like the carb you pictured, I vote for the manual secondary any day.
 
Black-Tooth said:
The other big difference between the emissions carbs and the others was that it had a VACUUM operated secondary!
Click to expand...

The vacuum-operated secondary was on the 28/30 DHTA, an emission-controlled piece of poo that was used only on the US-spec 1500 carbed cars in '79 and '80.

If you have a DHTA and don't have to worry about emissions inspections, there's a lot to be said for replacing it with a 32 DATRA, a 34 DAT, or a 34 DATR.
If you're transplanting a US carbed 1500 into a '74 and you want to preserve the '74 manual choke, then the 32 DMTRA/DMTR or 34 DMTR is the answer.
 
I just pulled the carb, you're right, it's a 28/30 DHTA. I'm glad actually, now I have something to look forward to when I upgrade it.

Any advise about removing the "Air Pump" (I think that's what it is) attached to the exhaust manifold? Can I just disconnect it? Is it hard to get the thing off? (looking to throw a set of headers on it)
 
tomnj said:
Any advise about removing the "Air Pump" (I think that's what it is) attached to the exhaust manifold? Can I just disconnect it? Is it hard to get the thing off? (looking to throw a set of headers on it)
Click to expand...

On a US-spec carbed 1500 engine, if and only if you are replacing the 28/30 carb...

There's a belt-driven air pump at the front/pulley end, on top. It pumps air (with a few strange and interesting doohickeys on the way) into a port in the middle of the cylinder head, on the sparkplug side. You can take it and the various doohickeys off. The port in the cylinder head must be closed with a suitable threaded plug; it opens directly into the exhaust manifold.

There's also an EGR valve, a sort of lumpy thing down low on the flywheel end of the motor, on the manifold side. Again, it and everything connected to it can be removed when you install your headers.
 
As Eric says, Tom...

Pull and plug everything and then make sure your vacuum advance works!

When you upgrade to a 32 or 34, a simple mod to the carb vacuum port will probably be necessary so that vacuum is NOT present during idle... see Best Of in Version 1.0 for details or get back to me.

You will NOT regret it!
 
Come to New Hampshire

Black-Tooth said:
If mine had A/C in it... it woulda been freezing your toes off with my homemade upgrades~
Click to expand...

We've got all the NATURAL AC you'd ever want....

-Always blows cold, even with the windows closed
-uses ZERO energy to produce sub zero temperatures
-no need to even run the fan! :)

refrigerated trunk, front and rear... Ice cream stays cold for weeks
As a bonus, you get free salt everywhere you go. Curb-side pick-up.
 
Eastep said:
By contrast I bought my '78 and the only emissions stuff on it still was the recirculating hose from the crank to the carb, charcoal canister, and vacuum advance. All of which will be gone once rebuilt.:eat:
Click to expand...

The charcoal canister and the crankcase breather line don't hurt power at all, and the only reason to remove them is to unclutter the engine bay.

I prefer to leave the crankcase breather connected because it doesn't get in the way much and because it's generally a good thing to apply some vacuum to the crankcase of a street-driven car... Keeps the crankcase better ventilated.

The charcoal canister has one hose that runs back to a plastic valve-doohickey thing by the driver's side wheel well. You can remove this hose, but you must leave the nipple on the doohickey open, and you shouldn't mess with any of the hoses and stuff behind it on the way to the fuel tank. They vent the fuel tank.

Look carefully at the vacuum capsule on the dizzy. Does it advance the timing or retard it? Early 1300 cars used idle vacuum to retard (yes, really!) the idle timing. If you have a vacuum retard, disconnect it and set your timing to about ten degrees BTDC, work from there to get a decent idle and no ping at full-throttle uphill acceleration. If you have a vacuum advance, you may find that you like the car more with it enabled.
 
I have had a bad experience with the small crankcase breath filter.
Last summer on a holiday trip I drove in the rain and the filter got moist.
Well heavy rain, here is a photo of me driving on the autobahn.



In about 600km I lost 3,5l oil.
Exactly, all of it, red light on.
After putting all the oil in I had with me, I looked for a petrol station.
This is how much oil I leaked, after standing still for a few minutes.



Not sure what the reason was, I took off the breath filter.
My oil leakage disappeared.
I'm pretty sure the moisture together with the oil fumes created over pressure.
This resulted in the leakage on the crankcase seals.
 
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