Topic: Weber jetting .

[Greg H]

Hi guys . I'm looking to buy a pair of italian DCOE 40 Webers for my project . The carbs can be purchased with my choice of venturi and jetting . What I need are some "ball park" jet sizes for 33/34 venturi on a 1000/1080 built motor just to get me up and running . Cheers Greg "H".

[Sam Green Racing]

Frank (754) might be able to help Greg, I think he had a similar set up.

Sam.

[Greg H]

I've exchanged a couple of PMs with Frank . I thought rather than pester him again I'd pester everybody else on here 

[754]

The ballpark specs are on here somewhere, not sure where mine are, I think Scottly may have them handy..

[scottly]

Hey Greg, you might want to reconsider those 33/34 mm chokes. After all, the stock intake spigots only have an ID of 28.5 mm or so, as I recall. If you use too large of chokes, you will end up enriching the main jets for proper mid-range RPM, which will tend to be excessively rich at high RPMs, at least in theory.    

[johno]

Hi Greg,
  On page 5 scotty has a webber thread happening,

I'm curious about your manifold brand ?

My limited experience with the big bores steered me into thinking the bore size didnt make much difference to the venturi size, it seemed to me the head and cam dominated the venturi size for a nice crisp mid to top range.

My pick for an average big bore would be 32mm venturis

On Scottlys thread I posted some jetting guides, I noticed on a few threads that some people got to run big main jets but I never had to run big mains and I feel they may have the emulsion tubes set up too lean and are over compensating with big momma mains.

So for your information but with disclaimer attached of course.

Available jetting !
Emulsion tubes  F16   Lean       control mid range, part throttle, accelleration
                         F11
                         F9
                         F7
                         F2     Rich

Air correction jets  120 Rich      Fine tune top end power
                             220 Lean

Main Jets         100  Lean    all range throttle
                       230 rich
Idle Jets  ? 50 F9 is good.

some examples.

Stock engine:  30mm venturis,  F11 emulsion tubes, 125 main jet, 200 air jets,  plus usual.
Stock engine: 33mm venturis, F16 emulsion tubes, 125 main jet, 190 air jet, 50F9 idle, 3/4 turn airscrew,
Stock bore , cam ports, 4 to 1,  31mm venturi, 115 main jet, 200 air jet, f11 emulsion,  idle 50 F9.
Float level 8.5mm

Dellortos x 40mm with 30mm chokes,  I set up on Yoshy 812, head, cam, 4 to 1. ;
Air correction jet 200, Main jet 135, Emulsion 7772.7,   idle 7850.4 and 50   go voxy!

I must say the once you have a webber set up its really exciting to book the dyno and use a gas anyliser to adjust the main, mid and low speed circuits.   The idle circuit often cant be perfect like stock carbs as they tend to be a bit fluffy especially with the 32mm venturis but that can be other reasons like accell pumps if squirted can take a split second to calm down,  but hey if it looks racy , sounds racy, goes racy ..... it probably is racy ...... lumpy idles kind of turn me on in the pits or traffic lights.

Good luck Greg !

[Greg H]

Thanks for the replies guys  . Very helpfull . Should help me  decide on which  jets/chokes to have fitted initially .