DCOE auxiliary venturi ?

L

Larry Frankenstein

Well-known member
I need some input on DCOE auxiliary venturi. I have set up DCOEs before on street cars but never had the knowledge, or need, to do anything with auxiliary venturi. Now, I am preparing to upgrade my HP 850 to the dual 40 DCOE set up. In looking into what my initial set up should be I came across information that suggests the auxiliary venturi should be a 3.5 “for up to 300cc per cylinder” and the 4.5 is “for up to 500cc per cylinder”. The wording “for up to” is not working for me. So my initial questions are:
- Is there any calculation or correlation between the main venturi size and auxiliary venturi size to determine which auxiliary venturi may be the “right” one?
- Does anyone have any experience they would like to share with using different sized auxiliary venturi?
- Are 3.5 auxiliary venturi available? I can’t find any.

Also, having gone through some of my Weber collection I have found a few DCOE parts which I would like to trade or sell as indicated below.

36mm chokes for 40DCOE 4 available. Would trade for 28s (my SCCA spec).
F9 Emulsion Tubes 2 available. Would trade for F11s.
145 mains 2 available. Would trade for 135 or 140s.

I hope to see some of you at/on the track in 2012. Not sure if that is a promise or a threat – maybe its both :)

Thank you,
Larry
 
No one . . . really?

Does anyone have a recommendation on any Weber gurus I can contact to get some input on the questions above?

Thank you,
Larry
 
Aux venturi? Do you mean the air jet?

The weber book I have has some tables and basic math to get close.

After you get it close, changing the air jet will move the main fuel jet response to a higher or lower RPM range.

You really want a air fuel ratio gage to help tune, should be able to find a cheap narrow band gage, but the wide band would be better.

I have a narrow band gage, which is better than nothing, helps to ensure you don't go over lean. Some narrow band gages just have 2 lights for rich/lean, but some are a actual gage.
 
Hey Ted,

The Aux venturi is in the throat of the DCOE, it is what you remove before you remove the choke (aka Main Venturi).

I have several books which have given me a starting point on the various metering parts (main, air, e tubes, etc) but the Aux venturi – no so much.

I have my header set up for an A/F gauge once I have the lil guy running.

Thank you,
Larry
 
Larry,

Here are a couple of suggestions. Try visiting lotuselan.net. In the search area, look up type26owner. Keith Franck has posted a huge amount of information on Webers and his attempts to make the carb work better. It will take a huge amount of time to go through all his posts on the carbs, but there is a lot of good information, along with corrections on the things that didn't work. One that did, was his method of setting float height, which works better than anything else written.

Keith posted on the Elan site for a long time before starting his own site on yahoo. His site is called sidedraftcentral, and discussing all things related to DCOE"s. It is also a place where you can ask questions of the members and get pretty good answers. Again, lots of information, some good, some bad. You will have to pick and choose.

One book you should have is by John Passini on tuning Weber carbs. Out of print, but can be found on Amazon. I found mine at Green Mountain Books in Vermont.

toolatesmart
 
Hi toolatesmart,

Re: lotuselan.net , Yahoo & Keith Franck, thank you will do.

Re: books. I have Hammill, Braden and A. Graham Bell. Re Passini looks like he wrote several, which one do you have? Tuning Tips and Techniques – or - Part 2: Tuning & Maintenance

Thank you,
Larry
 
I checked the 2 books that I have, one says there a about 12 diffrent Aux venturies available, but says nothing about how to select which one to use.

Sorry, let all of us know what you find out.
 
TED HEINRITZ":3yw0hg2i said:
I checked the 2 books that I have, one says there a about 12 diffrent Aux venturies available, but says nothing about how to select which one to use.

Sorry, let all of us know what you find out.
Click to expand...

I appreciate the effort.

Larry
 
Huh- well, thinking about it, it would seem that you'd want the least restrictive one you
could get that would give an adequate signal to the mains early enough to avoid that lean
dip as you come off the progression circuit.

Or in a race car, if the chokes are so big that you're having a hard time getting
consistent metering and response to jet changes, you could go smaller.

Frankly, I never thought about them until just now. But I probably should!

Thanks, Larry!

t
 
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