Weber 40 DCN 21 and 21A

Hi, I know that these carb variations were issued to different continents. 21's were Euro and 21A's were N America.

What I am trying to find out is how they differ? From what I can see having taken them apart they look to be identical, tuning parts are interchangeable between US and euro.
Are the differences inside where I cannot see?

If anyone can shed some light on this I would be most grateful, have exhausted google with various combinations of search but have not found anything definitive!!

 

I'm pretty sure the the differences are internal. There are primary jets, accelerator pump jets, emulsion tubes and more, all of which are likely to be different...

 

Like Venturi size, idle jet, accelerator cam, and air corrector jet.
It would be interesting to know the difference between the two.

 

Hi, thanks for the reply. Yes I am sure the above mentioned bits are different. My point is that I can change those parts to whatever I want. We all know Idle and Main Jets can be changed etc etc....
What I cannot find out is whether the designation of it being '21A' is a different internal design from the euro 21. Unless these were actually the same as each other in physical form and design but were just delivered with different jet sizes etc and designated 21A

 

I can't answer your question but I can tell you what I would look at. In the past, on 45 dcoes, I have found a different series number can mean a different progressive hole configuration. It is likely American market carbs would have a different configuration for emission reasons. I would look closely at this circuit before mixing and matching carbs.

Cheers Jim

 

As MiuraP400 has correctly surmised, the main difference between the 40 DCN 21 and 21A are the sizes of the holes drilled into the bodies of the carbs for the progression circuit. The fuel levels/float heights are also different between the two carbs, indicating that there may be other differences in the way the castings of the carbs have been machined.

If you look at the Euro 365GTB owners manual and the USA 365GTB owners manual supplement you can see all of the differences between the jetting and progression hole sizes of the two types of carburetor. I would not just re-drill a USA spec carb to the Euro progression hole sizes, because the location of the holes is also critical. Once you have modified a carb body it is very difficult to go back.

Pierce manifolds should know if there is any benefit to the modifications that you are contemplating.

 

Weber carbs with the changeable parts, You can arrive at a similar state of tune and have a complete different set of jets. People have jetted there cars correctly but the jet numbers they arrive at are not the same. Don't forget with this gas that is available at the pumps now, it doesn't burn like gas years ago.

 

Thanks guys.
Not planning on any modifications just wanted to find out the differences, as have a car in the garage that has the 21A's. It is running like a gem but wanted to find out out of curiosity.
No info in the webber documentation I have.

Thanks for the help, I'll try to post up the specs I am running for anyone else who it may help

 

Just one more thing I thought I would ask.

Does anyone have a copy of the US 21A Daytona carb settings so I can compare. The only documentation I can find is for the 20 and 21's.

Thanks again.

 

the 20s are/were ONLY found on euro-spec, EARLY version, GTB/4s
What they are, are: sand cast bodies
21 and 21/As are pressure cast aluminum castings

20s are super rare, were highly coveted for racing/hot rods, etc, as they can be adjusted FAR more-and more precisely, than the later versions...
the more commonly over looked oddities are the different accelerator pump arm RAMP ratios, combined with the progression holes(cam lift, lobe centers and duration was far more aggressive in the really early versions(I've seen as early as car 8, and several in the 1286x and below area....fwiw

They are porous, they warp VERY easily from heat, but much more so from over tightening of the base plates which in turn warp and pull the walls of the throats away from the axle's butterfly plates-which cause de-facto no-op of the progression circuit and a near impossibility to get an idle as you have no fuel regulation now....

21/a is slightly jetted differently to cope with the R2 points cuircuits...

 

How is your Italian?

this may help.
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View attachment carb settings 2.pdf

 

Amazing, thanks for that. Does not look like they differ too much, I'll get it to my Italian Mechanic Friend to translate for me!!

Thanks a lot

 

I have a lot of stuff around here. Sometimes it's even helpful stuff. You're welcome!

D