webers webers webers...

Scott -- One thing you might want to first check is if the progression holes are the same or not for these 40DCNF carbs from different series (I don't know if they are different or not, but IIRC there is some progression hole variation in the 40DCNF family). If they have different progression holes, you might need different jets/tubes to get the same overall behavior, or you might want to try to make a trade with someone to get a matching set of 4 (or at least four from the same series, even if you have some duplicates and have to get/make the needed hardware bits).

Also, don't assume that that table accurately lists the jets or tubes that are actually in those carbs -- pull them out and check the numbers printed on the jets, and Russ Turner posted some good photos showing the difference between the F24 and F36 emulsion tubes in this thread:

http://ferrarichat.com/forum/showthread.php?t=42363

Good luck with the project -- we like stuff like this so please let us know how it goes
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The jets should be the same for all 4 barrells. Steve is right (as he is about everything.. ) that each carb needs to be checked.

Carb 308 guys usually find that while the stock sizes are smaller, upping the mains to 135 or 140 make for a smoother better performing car. The technical reason is while there is a bit more richness, it importantly brings the main circuit in sooner, and makes a smoother transition.

The emulsion tubes (et's) are the magical soul of the carburretor personality (that and the transition holes, but they are not adjustable). Yes, while the earlier cars had the F-24s ('richer' if you will due to hole position and gas amount in the well); you can think of these as having some effect on the overall richness, but will be felt more on larger throttle movements. I think for your application, F36s would be a better choice with the richer main, but either is probably ok. Ask me why over a beer someday.

The air correctors come in to tune the high end mixture richness, typically coming in above 5500, but felt to a much lessor degree below. In your application, an A/C of 190 to 200 will work best for power keeping the high end down around 12-13 for power and anti-det protection. It's safer that way.

Idles - whoa nelly - These are more important than you think: it's important to know that you will probably spend most of your street driving on these (which you can control) and the transition holes (which you cannot, unless you want to drill the carb body). While this is variable depending on your transition holes, a good starting place is 53.

As Steve said, look at the transition holes and ensure they are the same; if different the difference will be felt below 3800 rpm and would be compensated by the idles, but it will be tricky.

Venturis - recommend use the stock 32s - they will give the best drivability with the best compromise for air velocity versus flow. You could go to 34 and pick up MAYBE some top, but your throttle response would be poopier due to lower velocities.

accel pumps - the stock size is fine as long as they are all the same - the honker -12 accel pump cam you have overcomes all (I checked from your photos). DCNFs have fixed accell pump bypass so nothing to adjust.

While RARE, sometimes these carbs came with different idle mixture screws. Look at the shape of the point.

There is never any real reason to use the starting mixture richness systems, so do not even hook them up. Most 308 owners never use them anyway, and it matches my experience with my Kjet to carb conversion.

Good luck, you are going to have a more reliable, more powerful, and a wonderful engine personality. It will be a hoot! We're all here to help.
best
rt

 

Impressive.
Recommend calling Pierce Manifolds, and:
Keep 32 mm venturis
Buy 8 x 200 a/c jets (cheap)
Buy 4 x 135 main jets (cheap) and use the other 4 135 mains for a total of 8
Buy 4 F36 ET tubes (not too bad), use with the existing 4 for a total of eight
Buy 4 x 55 Idles (cheap) to add using a total of 8 55's (It may be a little rich with these, but it will start cold easily and run smooth - can go down later if need be - ALWAYS err to the rich side. May want to go one step hotter plug - it makes a difference now that you have carbs)

Just have all of your accell jets be the same. Your needle valves I would bet $10 are all the same as it is, as most every DCNF is the same.
Call Pierce Manifolds and describe the idle mixture screw and get one that matches the others - it actually makes a difference.

Go to Walmart and get a nice tackle box for your spare parts. It's good to keep handy in it set of curved needle nose pliers, wide shorty flat bladed screwdriver, 8mm socket on a handle. Also a 17mm box end for the banjo fittings, I think.

These are all the parts you physically can change to 'tune'your car; everthing else ids for all practical purposes, 'fixed'.

If you haven't done so already, order a synchronometer - two makes it much easier. Four syncs is over the top, but better still.

Again, impressive attention to detail - I think you are going to have one fine running machine.

best of everything,
rt

 

Yes - the beauty of and immense popularity with racers for Webers is that they are soooo easy to rejet. I can rejet all 4 carbs in my car with the Webers on the engine in about 40 minutes, and jets are plentiful and quite affordable. I agree that the most expeditious thing is very simply re jet them all the same. Not much money, and results are the same. With the carbs out on the bench I am guessing 35 minutes tops - less than 30 minutes if you do not have a beer while doing it.

I'll again ask you to consider just leaving the cold start NOT hooked up. No one uses it, the car starts fine in the cold with a couple of blips on the throttle to prime, and Webers run a little rich down low anyway. And, it's one less thing to break.

Good luck and have fun!!

When can we talk about fuel pumps?
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I guess I don't understand the near-universal aversion to using the choke on these cars. I use mine regularly to keep the car at high idle for a few minutes while warming. It does a much better job than my foot, and also lets me do a visual check on the engine just after starting. After a couple of minutes, the rpms start to climb, and I just shut it off. Obviously the choke linkage needs to be adjusted properly so that they shut off fully, but that isn't hard to do. Also, 'cold' in SA is probably a little different than most of the rest of the country...

 

I guess it is due to adjustment issues on the choke.

Even on colder days three pumps of the gas pedal is enougfh to fire it up, and I catch the engine with the throttle as it fires.

It's just fun, to aggravate the neighbors with the manual warm up!

 

Of course, if he runs 55 idles, he may not need a mixture enrichment...

 

The problem is that the choke linkage doesn't actually physically "close" the starter (choke) valves inside the 40DCNF -- the choke linkage physically drags the stater valve spools up to open, but the final reseating of the starter valve spools for closing is done by the coil spring inside of the carb (the linkage just gets out of the way on closing). Even if the choke linkage is well-adjusted, if the starter valve spool hangs up inside its bore at the very end of its reclosing motion (due to a burr, debris, varnish, etc.), the cylinder will run super rich, and, if the car has cats, this is more trouble.

If using the choke is working well for you, I say all is good. Regular use or no use are both probably better than infrequent use so I think that's how the "no use" recommendation got traction (not enough "regular use" F Owners out there ), but you might want to check/clean/deburr/descratch the starter valve spools and bores occasionally -- JMO.

 

Scott:
I think you are getting good advice from thoughtful guys with plenty of experience. I'd be careful to be sure on the progression holes. Everything else you've mentioned is a service part that can be changed. There are (at least) two "variables" that can't be changed easily: the progression holes and the GAM air bleed. If you haven't talked to Mike Pierce at Pierce Manifolds you might call him (they are online at piercemanifolds.com) and confirm. A small difference here will, I believe, lead to a noticeable roughness in drivability.

As you know, the different "series" of the DCNFs (3X, 4X, 6X etc) are matched with respect to each other. Mike will know if they are similar (or be able to help you check/amend to make similar as needed).

Last, the mixture screws (I think you referred to them as idle mixture taper screws) do indeed have a taper to allow fine adjustment of the idle mixture. The Euro screws have a taper to a point (and are "better" for tuning). The later US screws have a shoulder (an emissions regulation impact) and are a much blunter instrument.

HTH
Philip

 

Fascinating stuff in here, thanks guys!

Makes me want to unscrew my airbox thumbwheels and gaze down in there with amazement.............

Thanks also for that chart, I will add it to my documentation.......

 

I think a few of us would be more than intersted....

 

The first thing I had to do on #22127 was go thru my carbs, as the Technician mentioned....."I think this car was running good, as it left Maranello!"

Although to read Phil Hill's tales on the 6C racecars, this was not always the case there....sometimes they needed some "love" trackside......

We went back to 'stock' on my 1977s and I'm happy! I have no idea what that was........

From there, we moved on to distributor advance, and rebuild.......

 

Steve, thanks for the excellent explanation, as always.

I bet those guys running 60 idles REALLY don't need a choke.