Dell'Orto AS v BS

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duccout
Cucciolo - the Lil Pup
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Joined: Tue Oct 27, 2020 8:55 am

Dell'Orto AS v BS

Post 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?.
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Craig in France
Paso 750
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Re: Dell'Orto AS v BS

Post 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 ...
duccout
Cucciolo - the Lil Pup
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Re: Dell'Orto AS v BS

Post 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
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Craig in France
Paso 750
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Joined: Tue Mar 23, 2004 3:58 pm
Location: Montpellier, France

Re: Dell'Orto AS v BS

Post 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.
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