Jump to content

14th Annual SoCal Vintage BMW Meet 2021! “All couped up”

Registration is still open. Rally from NorCal is scheduled for Friday. Post your event photos.

SoCal Vintage is Here! 

Post your photos!

Weber Dellorto Question...


Recommended Posts

Similar sidedraft designs from 2 different companies. Similar performance. Dellorto's are not as common and are not made anymore. Harder to get parts but they are still out there. Maybe less people know how to tune and work on them. I hear they have a great idle circuit so tuning them to idle is easy. Webers are more common, easier to get parts and rebuild kits, more shops have experience with them, maybe a bit more finicky. Performance wise, its about the same with maybe the nod going to the webers. Th Dellorto's I have heard are designed more for a sreet car, and Weber's are designed more for a track car. That being said...many a car was delivered from the factory with dual and triple webers...triumph, alfa romeo, ferrari, bmw, lotus, etc...so they live just as happy on a street car.

Link to comment
Share on other sites

Properly adjusted and in tune, there's little difference between the potential of the Weber DCOE vs. the Dellorto DHLA carbs. But, the Dellorto is not merely a copy or clone of the Weber.

There are distinct differences between them. In general, I would prefer Dellortos over Webers, all other things being equal. I'm not trying to start a Carb War here, they are both very good carburettors. If you prefer, know, or are experienced with Webers, stick with them.

So far as parts availability is concerned, it is same-same. It's just that there are many more sources for Weber parts than Dellorto parts, but Dellorto sources can fix you up with any part you want.

A major difference between the two is in their precision parts. You can tune a Dellorto to a much finer calibration than a Weber. This is partly due to the fact that Dellorto calibration parts, like jets and mixture screws, are available in a much finer resolution. Weber Main Jets are available in size steps of five hundreths of a millimeter (0.05mm) - (130, 135, 140...) while Dellorto's are available in steps of one hundreth of a millimeter - (0.01mm) - (131, 132, 133, 134...). This is the same with Idle Jets, Accelerator Pump Jets, etc...

The Weber Idle Mixture Screws have blunt tapers and coarse threads, while Dellorto's have long slender needles and fine threads. The later "E" models (40E & 45E) have even longer tapered needles and finer threads. Weber mixture screws typically end up adjusted about 1 1/4 - 2 1/4 turns out, while Dellorto screws end up 2 3/4 - 3 3/4 turns out.

Because of all this, overall, it's much easier to dial-in a very exact mixture setting with Dellortos, while with the Webers, the variance is much wider and less exact.

Also, the Dellorto is ported to accept a manometer, whereas the Weber has to rely on less precise airflow meters for tuning. It is much easier to get an exact setting with a manometer, and you can set it with the air cleaners and filters in place and compensate for them.

One potential advantage of the Weber is the ability to swap jets by simply turning the 'Mouse Ears' and removing the jet cover whereas on the Dellorto you have to remove the carb top. I say potential advantage because except for track use, where jets are frequently changed to comply with temperature, humidity and barometric pressure differences, in a street car, how often are you really doing this? The downside is that you have two additional seals to potentially leak. On the Dellorto, because it's gasket is reuasable, it's really a more reliable design, and really isn't any more difficult to swap the jets, except that you do need a screwdriver.

The Dellorto also has the edge when it comes to off-idle transition. The Weber progression circuit often has only 2 or 3 holes, while Dellortos have 5 or 6. Dellorto developed a 6-hole progression model at the express request of Lotus Cars for their 91X engine used in the Eclat, Esprit and Turbo Esprit. Dellorto later adopted this innovation across it's entire product line.

The 6-hole setup gives the Dellorto a much smoother progression off-idle so the carbs are less dependent on a heavy shot of fuel from the accelerator pump. On the other hand, the Weber can experience 'flat spots' at certain RPM, and requires a big pump shot of fuel. This shot of fuel can affect significant wear on a Weber carbed car vs. one with Dellortos. Weber carbed engines often experience significantly shorter piston ring life compared to Dellorto carbed engines due to the Weber pump shot constantly washing down the cylinder walls.

Carb wear itself is another factor. The Weber accelerator pump's piston runs in a bore machined into the body. It experiences metal-to-metal contact, this subjects it to "blow-by" because of clearances, and tends to wear over time. Unfortunately, this bore cannot be repaired and therefore goes further and further out-of-spec. The Dellorto uses a diaphragm pump which has no blow-by and clearances don't wear with use. When it does get old, the pump is easily rebuildable back to spec by simply replacing the diaphragm and gasket.

Weber's are also more prone to leak and smell of gas. Strictly speaking, the DCOE is a Race Carb and so one of it's design criteria was that it be designed to work with alcohol. Dellortos use Butyl rubber gaskets while Webers use paper gaskets (alcohol attacks Butyl rubber). Paper gaskets are more leak prone with time than Butyl ones. Lotus switched to Dellortos with their Esprit and Eclat models specifically to solve persistent fuel leak issues they experienced with Weber DCOEs in their Twin Cam engines.

As I said, they're both great carbs. If I bought a car that already had Webers, I'd keep them in place, but, if I were building-up a carbed engine from scratch, I'd go with Dellortos over Webers every time.


Link to comment
Share on other sites

Very interesting comparison. The Dellorto tuning book by CB Performance is a very good reference, but I don't think it has all of the information you posted.

You can get parts from CB Performance in Farmersville, CA





Weber carb rebuild kits and jets are also available from CB


Link to comment
Share on other sites

02for2, very nice summary.

When we ran a 2002 shop in the '70s, the Dellortos were the weapon of choice. In real world shop terms, the easy to fiddle accelerator pump diaphragms and the fact that the fine thread idle mixture screws had a much wider adjustment range for a tuneup - if you had big jets in a Weber, you could kill the idle in 1/8 turn - made them a mechanic's favorite. I still run them.

Link to comment
Share on other sites

I have DHLAs on my 2002. I like them a lot. I'm just starting to learn how to fiddle with them and I am pleased with how responsive they are to my efforts.

If you're running a set of DHLA's, a Morgan Carbtune II - http://www.dellorto.co.uk/merchandise/products_details.asp?PartNo=MANOMETER4&CategoryID=8&PartsectionID=17 is an absolute must have.

With the Carbtune II you can setup and sync all 4 barrels at once.

Also, you can get the brass adapters and 'O' rings which you can permanently install on each carb. Use simple vacuum caps to cap them off.

Then whenever you want to tune or sync the carbs, you just pull the vac caps and attach the rubber tubes from the Carbtune II making tuning the carbs a less than 10 min. job.

It may cost a buck or two to get set up, but the payback will be better fuel economy and less engine wear making this a pay-for-itself kit.


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...