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Dell'Orto AS v BS

Posted: Tue Nov 16, 2021 9:12 am
by duccout
Does anyone know what the difference was between Dell'Orto AS and BS carbs? I suspect that it is simply that the AS had no choke assembly, but the BS did, but strangely, the AS 40MM used no. 60 pilot jets and the BS used no. 65 pilot jets, so possibly there was an internal difference too?.

Re: Dell'Orto AS v BS

Posted: Wed Nov 17, 2021 5:49 am
by Craig in France
You know, Colin, this question comes up every now and then and I'm still not clear ...

According to Dell'Orto themselves, that 'A' / 'B' / etc designation on both the PHF and PHM carb ranges describes the type of connection to the engine. But there is inconsistency between PHFs and PHMs.

PHF: 'A' is what they call a 'clip fitting'.
'B' is a 'flexible fitting'.

PHM: 'B' is now the 'clip fitting'.
'E', 'H', and 'N' are 'flexible fitting'.

And even this semi-logic doesn't seem to apply to the PHB carb range where the 'G', 'L', 'H' and 'E' designations seem to be used in quite another way ...

Re: Dell'Orto AS v BS

Posted: Wed Nov 17, 2021 6:40 am
by duccout
Hi Craig,

It seems funny to me that the 40mm PHM B equipped Ducatis had no.65 pilot jets and the PHM A bikes had no.60 pilots. When I changed my S2 to 900SS spec I changed all the jets to the earlier settings but the engine would not run properly without the bigger pilot jets, so I believe that there is more to this than just the addition of chokes.


Cheers,

Colin

Re: Dell'Orto AS v BS

Posted: Thu Nov 18, 2021 3:57 am
by Craig in France
Makes sense, Colin. There was a similar story with Dramahs.

They went from PHF32 'A' to PHF32 'C' (i.e a designation that had nothing to do with the type of mounting :?), and from a 60 idle in the former to a 62 idle in the latter.

But what wasn't shown was there was an internal restrictor fitted as well. All to do with emissions, apparently.

Might well be the same story with the PHMs. Steve Allen knows about more about this than I do - hopefully he'll pop up soon.