I understand that the carb main jets for monobloc and concentrics are the same and jetting should be similar for both these carbs. But what is with the promonoblocs, are the jet sizes also comparable?

I thought the size related to the flow rate and the engine requirements should, logically, be much the same independent of the carb used.

I have found various specifications for jetting a B31:
Monobloc with filter jet size 200
Monobloc without filter 260
Pre-monobloc 150 I haven’t found anything regarding filter/no filter for the 276 carb.

Now that seems to be a fair difference between 150 and 260 between the two different carbs on virtually the same machine

Similarly for a B33 there is a difference quoted; 200 for a 289 and 260 for the 376 carb.
M20 is 170 and 240 respectively.

Have I missed something fundamental here? :thinking_face:

If anyone can enlighten me I’d be grateful!

cheers
Pete

email (option): petercomley@web.de

Hello Pete,

This is out of "The Amal Carburetter company Reference Catalogue", if it helps...

Cheers,
Noam.

Thanks Noam

This also shows the difference between 289 premonobloc and the Monobloc 376 for a B33.

For the 376 carb the main jet is either 210 or 260 depending on whether an air filter is fitted. The 289 carb has a 200 jet.

Is this with or without a filter? Even if it is with it is a smaller jet than the Monobloc.

Did the earlier engines need a smaller jet? Or is there some fundamental difference that makes the promonoblocs run richer for a comparable jet size?

Cheers
Pete

email (option): petercomley@web.de

Hello Pete,

The same book aslo states"The same design of main jet is used on all of the current carburetters,
excluding the 276 and the 400 series"
Maybe the difference in design has to do with that?...

I guess the method of numbering the jets is the same in both Amals, and not different as with "Dellorto", for example.

One numbering system represent the "hole"/drill size in the jet, and the other goes by the flow rate.

Best regards,
Noam.

main jets

Monobloc and concentric



premonobloc


they are obviously different but I thought the number always refered to the flow rate.

email (option): petercomley@web.de