anything's possible, but your 40 F6s are hard to compare with the preferred 50 F9 without testing it.  On the one hand, the F6 idles are richer than f9s, but a 40 is leaner than a 50, so what do you end up with?  Richer? Leaner?  Try to borrow some idle jets before your track day.  Are you saying that your engine runs pretty flat from 5000 and up all the way to redline?  Or does it just have a lazy spot at 5000 and then recover to continue revving higher?  If you're flat at 5000 RPM, this is well beyond the RPMs where an idle jet has much of an effect, so I suspect you my be lean at 5000 and from then on.  Almost any healthy A-series engine should be able to rev enthusiatically way past 5000 to 6000-6500 anyway.  Your 135 main looks tiny and could be inadequate for your engine.  The ideal would be for you to either use a good wideband A/F meter or run your car on a chassis dyno.  In either event, you would be seeking information about the A/F ratio at different RPMs so that you could tune the carb more intelligently.  Unless you have A/F readings, you either have to rely upon your own expertise or someone else's.  Remember to tune one problem at a time.  Your 55 F9 idle is close to the 50 F9, so you may find mor benefit from trying a richer main jet, but work up in increments of, say 10, so that you don't run past your engine's "sweet spot" for main jetting.  Try 145, then 155, until the top end improves.  It's pretty darned unlikely that you are too rich with only a 135 on a 1380.

Bottom line:  you are running tubes(F2), airs(180) and idles(55 F9) that are either close to, or right on, what most other big-bore users run, so your problem(s) may lie elsewhere(like the 135 main).  I would change mains before changing out your 32 chokes.  They MAY be on the smallish side, but not drastically so.  Plus, jets are cheaper.  See if you can richen the mains and get the engine to rev harder over 5000 problem area you have no.  See how the engine responds to main richening and report back.

It's hard to make carb suggestions in a vacuum without knowing if the rest of the engine is OK.  As an example, is the ignition timing and curve correct?  Are the cam timing and valve clearances correct? You get the picture.

Thanks. I'll try to find a pair, but Track day is Friday.

How about my spare 40 F6's? Or would that be going too far?

Also, the engine seems a bit flat when it gets to 5K RPM's. It's been okay for the street, but on the track a little more oomph up high would be nice.

Would any of the aforementioned 'spare' parts help? (They will be replaced one at a time, honest :-)

Thanks very much,

Jim

The greatest tragedy in mankind's entire history may be the hijacking of morality by religion. -Arthur C. Clarke  (1917-2008)

At last, the rest of the current setup;

Air Correction: 180  Emulsion Tubes: F2  Mains: 135  Idle: 55F9

(As a matter of interest, I found the DCOE40's from my old race car. Setup, in the same order, is: 130, F16, 115, 40F6. If any of these can help my Mini, it would be an easy change, and come in handy at "Track Day" at Summit Point on Friday)

Many Thanks 

The greatest tragedy in mankind's entire history may be the hijacking of morality by religion. -Arthur C. Clarke  (1917-2008)

I forgot one other good source of Weber information.  It is a new book which is a compendium of two previous books by the same author, John Passini.  Now, Passini has some detractors, but I have found some solid information in his book that I have not found in the other Weber books generally available.  No one book gets it 100% right, anyway.  In only 40+ years of reading automotive books, I have learned that it is sometimes useful to read several books on a subject, such as Webers, and then sort of intuitively "average" the information from  all of them.  It may not work for everyone, but it has served me well.

The Passini book is quite reasonable at about $13.37 from this source and provides at least some coverage of non-DCOE carbs.  The book is largely about DCOEs, in general. http://www.amazon.com/Weber-Carburettors-Tuning-Tips-Techniques/dp/1855207591/ref=sr_1_4?ie=UTF8&s=books&qid=1210630911&sr=1-4 

Jim,  I am devoting energy to this thread in the hope that it will help others in addition to yourself.

I stand corrected.  Emulsion tubes do have a significant effect at the low-to-mid range of RPMs and throttle opening.  You can't believe everything you read, but most 1275-1380 motors are running F2 tubes.  This doesn't mean it will work everywhere, but it does work acceptably for a lot of folks.  So I would be hard pressed to suggest changing it when so much of your setup is unknown to me.  I still say that a starting point would be to check your idle jets.  Once again, a lot of folks find that the 50 F9s work pretty well.  We haven't even mentioned your pump jets and pump bleed valve opening yet.  So, there is a lot to consider for improving your carb which is somewhat close already.

On another subject, I forgot to mention another book which is useful in learning about how Webers work and how to tune them.  This is from a seemingly unlikely source since the authors work with air-cooled VWs and therefore downdraft Webers, but most of what they have to say can also be applied to DCOEs.

The book is  "Weber Tech Manual" written by Bob Tomlinson of CB Performance, formerly known as Claude's Buggies in the old days. It has a really excellent troublshooting section among other things.

The book covers almost all modern Webers available and gives significant coverage to DCOEs and downdraft carbs that may be suitable for the A-series engines. 

The book might be available from Amazon for $17.95   http://www.amazon.com/gp/offer-listing/B0006F1KBM/ref=dp_olp_2?ie=UTF8&qid=1210460686&sr=1-1

But........ 

I bought mine directly from CB Performance (in Central California).

At only $10.95 from CB Perf. this book is outstanding value.

They also have a similar book on Dellortos, again from a VW perspective.

http://www.cbperformance.com/

Thanks for all your time and devotion to 'the cause'. :-)

As soon as I get the Mini back from the body shop I'll check the other jets.

The greatest tragedy in mankind's entire history may be the hijacking of morality by religion. -Arthur C. Clarke  (1917-2008)

jim,  it's really  hard to say not knowing about your idle jets, in particular.  Almost everyone running big block Minis, either on the road or the track, runs the F2 tubes.  They are recommended in all of the books and seem to work pretty well for most folks.  I run them in my 1315 engine in a 45 DCOE.  I would really want to know which idle jets you are using before making any other recommendation of changes.  Lots of folks are happy to run the 50 F9 idle, but I would have to take into consideration which other bits you are running and not specified here.  If it turns out that you are not running the 50 F9 idle jets, you may want to borrow or buy a pair and throw them in.  As I said before, your 135 main jets seems smallish by comparison with what I have seen and heard, but they also have more of an effect at the higher RPMs.  You say it runs pretty well as-is without the stumble, so it sounds like things are fundamentally OK, and only needing some fairly fine tuning.

It is also worth considering which auxiliary venturi you are using.  This piece has a strong role in determining the strength of the input from the emulsion tube assembly with mains and airs, so if this is wrong, you could be bodging that transition from idle to mains. 

The cardinal rule of Weber tuning, and most other types of tuning for that matter, is to only change ONE thing at a time.  Otherwise you're liable to take one step forward and one step back and assume that neither change made any difference because they cancel out each other.

It may turn out that your chokes are a bit smallish at 32mm, but they would mostly affect top end more than the transition.  Since chokes are expensive and idle jets are cheap, try the idle jets first, if they are not already 50 F9s and evaluate the effects from that change.  I would hold off changing to larger chokes because they have more effect at the top and because it is better to have chokes too small rather than too big.  Smaller chokes, within reason, cause a higher velocity of airflow resulting in stronger "signals" to the rest of the carb's components.  The engine will seem more responsive as a result and will react more strongly to jetting changes. 

I'm just giving you food for thought here and am not really making any recommendations except to the idle jets if thay are not already 50 F9s.  Good luck at Carlisle ! 

declanm,

 The Mini is currently at the body shop, getting a 'facial' before the Carlisle show next week. 

 Once I get it back I'll check those jet sizes and get back to you.

  I'm wondering if a quick and dirty first attempt to fixing the 2000-3000 constant speed stutter might be to replace the emulsion tubes. If so, which direction should I go?

  Many thanks. Hope I see you at Carlisle. Mine's the red one. :-) 

The greatest tragedy in mankind's entire history may be the hijacking of morality by religion. -Arthur C. Clarke  (1917-2008)

The Innovate LM-1 unit is designed to be used in moving as well as stationary cars and engines.  Some very well-respected chassis dynos have an LM-1 attached.  Some race cars have them installed and use them during races.  One of the reasons why this is possible is that the LM-1 has logging facilities which allow you to capture around 45 minutes or much more data that can be processed after the data collection is complete.  Graphs can be produced by the LM-1's software and spreadsheets like Excel can digest the captured data and make it more easily interpreted and understood.  So please ignore any of the naysayers who don't think an A/F meter is useful throughout the RPM range, in any gear and under any load(hills).  They wouldn't be very useful, would they.

Anyone wanting more information of the use of the LM-1, specifically, would be well advised to examine the Innovate-maintained forums which have some very useful information contained therein.  The forum is at:  http://www.innovatemotorsports.com/forums/index.php  and the Innovate homepage and product listing is at:  http://www.innovatemotorsports.com/

Before anyone asks or speculates,  I must admit that I get a 5 cent commission for each LM-1 sale that I help to be sold. Shame on me. 

jimarnett-  which auxiliary venturies idle jets and pump jets are you using? 

It seems like a small main without knowing the size of components I listed above. 

Thanks for all the useful advice

1. I will definitely check out the Yahoo site

2. Don't have an airflow meter yet. Any suggestions? Too bad you can't just rent one. Everything I hear about Webers (and remember from several Alfas) is that once they are right, they stay right,

3. Some carb/engine details: Air correction=180, Emulsion=F2, Main=135. Cam is an APT V7, so durations, In/Ex are 256/272. Compression ration 10:1 (Omega pistons) 

4. My email address is as in the profile, but delete the word 'ignore'. Make sense?

 THANKS FOLKS!

The greatest tragedy in mankind's entire history may be the hijacking of morality by religion. -Arthur C. Clarke  (1917-2008)

I would not say that 32mm is too small, and even if it was, all it would do would be to curtail the top end a little ( in the case of a 1380, beyond about 5,500 rpm. Poor progression is nearly always down to the emulsion tubes, which are very difficult to match to siamese port engines because of the uneven firing intervals which provide an unreliable airflow signal.What tubes are you using at present?

 The other culprit can, of course, be the cam. What are you using, because anything with more than 276 duration will be a bit problematic on the road ?

you don't mention which A/F meter you plan to use or what your carb settings are.  Here's a great website http://www.innovatemotorsports.com/forums/index.php  that is really targeted at users of the Innovate LM-1 A/F meter.  Even if you don't use the same A/F meter, there is a lot of DCOE tuning info on the site. 

Additionally, there's a Yahoo group named sidedraft_central.  To access this group, you'll need to have or set up a Yahoo ID.  Since this group is oriented strictly at sidedraft carbs, mostly Weber DCOEs, you may find it easier to get answers to your own questions from this source.

Best to check out both sources. 

There's a good book, see http://www.amazon.com/Build-Power-Dellorto-Carburettors-Speedpro/dp/1903706750/ref=sr_1_2?ie=UTF8&s=books&qid=1209867435&sr=1-2

This book even has information that is specific to A-series engines with their unconventional siamesed intake ports. 

Thanks folks.

The Mini IS runnning, and running fairly well. But there are some rough spots during the 'transistion phase', around 2500, that I'd like to take care of.

Also, it's running 32 venturis, which I think are a bit small for a 1380 with a cam, 10/1 pistons and a LCB. If I change the venturis, then I'm back at square one with setting up the carb.

Rumor has it that there's a guy not too far away with a dyno, who knows BMC "A" engines and Webers. I'll try to find him... 

The greatest tragedy in mankind's entire history may be the hijacking of morality by religion. -Arthur C. Clarke  (1917-2008)

You will not find a cookbook such as you described, but there are plenty of references to help you select a good combination of parts for your carb.  You should quickly be able to pick a set of jets which will at least allow it to start, idle, and run smoothly enough that you can get the car moving and see if it will transition from the idle circuit to the mains under a load.  After that you can really begin tuning, if you can't get to a dyno then road driving with an A/F meter will be useful, but there is much that can be done without it. My favorite guide to the Weber is "Setting up and tuning Weber DCOE Carburettors",  a collection of reprints from Ford's Boreham workshops where the works rally Escorts were built and prepared.  These first appeared as a series of "Carburettor Chats" in the Technical Bulletins issued by Ford in 1974 to members of the Ford Rally Sports Club. It is, or was, available from Wallage Reprints, the ISBN number is 1 84147 0023.  Any book like this will explain first how to select the jetting, then how to set up and tune the idle, what to observe during acceleration and cruise tests on flats and on hills, what to change (and which way to change them) in order to have a desired effect, and how to read spark plugs.  

Your A/F meter instruction manual should explain how to precondition the new sensor, how to clean it if you contaminate the sensor, how to interpret the display while driving.  Most of them provide an analog output signal which can be recorded, if you can borrow some data acquisition gear.  If you aren't recording, bring along a copilot to take notes of RPM and A/F.  Slow acceleration, coasting, and constant rpm runs of 10 seconds or more will give reliable (human recorder) readings.