Weber Carby Genius wanted!

[71TA22]

FYI,

I run pretty much the same carb jetting set up with a 1940cc hybrid with DCOE 45's. 282 duration (Lotus L14 spec) cams and 88260 more agressively ported head.

Emulsions: F16
Idle jets:55/F9

Good idle, poorer progression, wants to go much higher than 7.5k rev limit.

I know I need to get some good con rods and do a full balance to exploit this potential.

[jb_22]

Cool info Mike, it's good to hear from people with their experiences.

I have 195 air correctors & 7772.11 emulsion tubes, thinking they could also be leaning it out a little too much as well. Once I get a drill bit we'll see how the 135 main jet goes.

[Nevakikamukau]

Jess,
I can recommend a good book on tuning Dellortos and Webers. It is called "How to build and power tune Weber & Dellorto DCOE, DCO/SP and DHLA Carburettors" by Des Hammill. In this book Des Hammill recomends the following initial selection of choke sizes:

Choke sizes (on the basis of one choke per cylinder)

28mm chokes: 250cc per cylinder;
30mm chokes: 300cc per cylinder;
32mm chokes: 350cc per cylinder;
34mm chokes: 400cc per cylinder;
36mm chokes: 462cc per cylinder.

As your motor is 1790cc which is 448cc (say) per cylinder, 34mm is the go for your situation according to Des Hammill.

There is also another Dellorto guru on the web called Dave Andrews (http://members.aol.com/dvandrews/dellorto.htm) who gives a chart showing main venturi sizes for various engine sizes and rpm range. Extrapolating from Dave Andrews chart for a 1790cc motor with 6000rpm rev range a 33mm choke is required. For a 7000rpm rev range a 37mm choke is required. If the above link gives you problems then just Google 'Dave Andrews Dellorto' to see his recommendations for setting up Dellortos & Webers (amongst other things).

In view of this, I still feel a 34mm choke would be best for your situation.

Cheers,

Peter

[jb_22]

Ah to the rescue again Peter! How much low-down driveability would I lose with 36mm venturis/chokes? I'd probably need 140 main jets to go with them.

Also thinking about investing in one of these: http://www.diyautotune.com/catalog/i...c9895b6d7873a0

Cheers, Jess

[Nevakikamukau]

Jess,

It is a trade off of velocity against volume. You would loose tractability low down with the 36mm chokes - by how much I don't know. It depends upon what you want your motor for. If you want a good road motor with tractability through the rev range then go for 34mm chokes. If you want a race track or drag strip screamer then go for the 36mm chokes. From what you were saying in previous posts your motor was going quite well until it hit the wall at 5500rpm. I think this was probably because your small chokes were starving the motor at high revs and not enough air/fuel mixture was getting into the cylinders. If I was you I would work on one parameter at a time. Get the chokes right first and then worry about the mains. I don't think you will necessarilly need 140 mains. With your 60 idles, I think 130 or 135 mains should do the trick. Get the chokes right and see how it goes before you invest in more main jets.

[71TA22]

jess,

I have an alternative set up for the DCOE 45's.

Chokes: 38mm
Mains: 160
Main Air: 220

This wont idle properly and has a huge flat spot up to 3.5k revs. After that it sounds great and goes even better.

This setup is hopeless in town as it wants to stall. Its hopeless on the highway unless your happy to sit in third gear all the time.

Its only suited to a race track.

Go with the 34mm chokes and get your jetting worked out round them first. The last thing you want is a car thats a pig to drive on the street.