Re: [alfa] Weber vs. Dellorto

["Dean" <tessiedog@xxxxxxxxxxxxx>]

Dellorto pump jets are also adjustable in there stroke lenght and jet size.
Most older italians will tell you that dellortos are better at making power.
Maybe they a biased. I have only ever used dellorto's and am still able to
buy new parts for them with the exception of venturies which can be
machined. The dellortos as fitted to alfas have a fixed air bleed on the
idle jet and thus are difficult to tune for hot cams. In anycase you should
use 45mm carbs with hot cams and 45mm dellortos have adjustable holesfor the
idle circuits situated on the idle jet carrier. This is not so well
understood and is the reason people suffer to tune the transition phase from
idle to main jet when useing hot cams.
Dean
-----Original Message-----
From: Greg Hermann <bearbvd@domain.elided>
To: Bill Sinclair <bills@domain.elided>; alfa-digest@domain.elided
<alfa-digest@domain.elided>
Date: Wednesday, 5 May 2004 6:20
Subject: Re: [alfa] Weber vs. Dellorto


>At 10:17 AM 5/4/04, Bill Sinclair wrote:
>>  I'm
>>definitely not a carb expert but the biggest physical difference I see
>>between the two types of carbs is the accelerator pump.  On Webers, it's a
>>piston type and on the Dellortos it's a diaphragm.  The diaphragm seems to
>>give a much longer squirt of fuel (in duration) than the piston.  As to
>>whether that's an advantage or a waste, I couldn't say.  Perhaps Greg or
>>someone knowledgeable about the inner workings could comment.
>>
>>Bill Sinclair
>>67 Duetto
>>73 Berlina
>>--
>The length of the 'squirt', or pump shot, on a Weber DCOE is completely
>adjustable. The size of the accel. jets is part of the main circuit
>metering--since they DO act as a far top end enrichment device. Once the
>main circuit tuning, including the sizing of the accel. jets is correct,
>the RATE of pump squirt may be adjusted by changing to stiffer or softer
>pump springs (with stiffer giving a higher rate). Once the rate of squirt
>is where it needs to be (instant throttle response with no rich stumble
>either) , the duration (total volume) of the squirt may be adjusted by
>changing the pump return jets (a larger pump return jet shortens the length
>of the squirt). If you get down to a closed pump return jet, and the squirt
>STILL isn't long enough to suit you, then you can change the length of the
>pump rods, and thus the length and volume of the pump stroke (stock pump
>stroke is 10 mm, rods which will yield a 14 mm stroke are available. Too
>long a squirt can usually be detected via instant throttle response
>followed by a bit of a rich stumble and perhaps a puff of soot in the
>exhaust, while too short a squirt manifests itself as instant throttle
>response followed (very quickly) by a brief lean hesitation.
>
>I don't know the Dellorto's all that well. Diaphram type accel pumps in
>general have a reputation of initiating the squirt marginally quicker than
>piston pumps do. I am a bit skeptical of this claim--but AM aware that
>Weber used diaphram pumps on their IDA type carbys (the downdraft brothers
>of the DCOE's).
>
>You absolutely MUST have the main and idle circuits properly tuned (no
>over-rich messes need apply) before any hope that tuning of the pump
>circuit can be done properly can exist.
>
>Greg
>--
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