more emulsion tube questions

I recently changed my emulsion tubes from F36 (140/190 jetting) to F24 on my '75 GT4.
I experimented with various jetting configurations for the new emulsion tubes starting from 125/220 (the car ran like crap) on to 130/200 (can ran better but with a pronounced flat spot in the transition from idles to mains) to 140/200 (better but seemed to lean out on the top end) to 140/190 (best configuration so far). It feels too rich at idles and low rpms but it really flies above 4000rpm and there's not much of a flat spot anymore.
I haven't touched my idle jets yet (55).

Rocco

 

I would start rich with 135/200 and work lean, first mains, then a/c.

Ferraris tolerate rich, and it does cover some holes. Also, as the weather cools, the car will like the richer jeting a bit more.

The ETs, while they will change the steady state A/F a bit, the mixture and response in transitions is where you will see a "change in personality". For example, there will be more gas in the well with an F24, ready for use in throttle changes.

If you can run F24s as originally designed, I really think the car does better with them.

 

My bet: 50 or 53 idles, keep the 140s.

 

I was surpised too when I ended up with the same jetting as the F36. I don't really understand why, but I couldn't get the car to run right with any other configuration.
I haven't been able to do a dyno run since the change so I don't know what the numbers are.

Rocco

 

The plugs look a bit dark, but there's not much soot there. I was planning to put in fresh plugs in soon as I haven't changed them for 3 years and 15k miles.
The F24 improved throttle response above 4k rpm, but not below that. The rush to redline is more intense but in town drivability is not as good as before.
With the F36s I had better low end torque and drivability but the it felt like I was running out of steam before red line (on the dyno peak power came in before 6500 rpm). I would bet that my peak power now is closer to redline.

Rocco

 

I currently have F24, 125's and 200's, 55 idles. Top end fine, a bit boggy around town, I suspect I may need to richen up my accelerator circuit when the go pedal is depressed,and I think I may need 120's and 50's due to my altitude, but I won't know for sure until i get it on a dyno and get a wide RPM range AFR readout.

I also have crappy smog/cat cams, with no cats anymore.

Doug

 

So just why are you guys revving your Ferraris below 4000 rpm?

Seriously, at least in my experiience, around town drivability is more to idle/main transition because of slow butterfly movements between 2800 - 3800 rpm - on the LM-2 A/F meter you can see these slow movements not readily firing the accell pump depend on good hand-off between the idle/transition and main circuit. Just as our friend has said, the ET's are more noticible once you get the adrenaline going, i.e. above 4K.
Just my experience.
I love hearing about your results - I learn something every day.
Best
rt

 

John, as you may know, there's a very good chance that what works for somebody else won't work for you, either because of altitude, wear on the carbs (butterfly plates or shafts, for example), gasket leaks, etc. My experience with dcnfs, idas, idfs has been that it's not so common that the same jetting works on theoretically identical engines.

One tip - check to make sure the progression holes in the throats are all the same. Frequently, after 20+ years of mucking with the carbs it's common for one or two to have been replaced, and sometimes with a non matching weber with different progression holes. The progression holes have as much to do with the transition from idle to part-throttle as does jetting.

You'll probably have to mess with idle jets and the accel pumps as well as everything else to get things really tuned nicely. Good luck and persist!

 

You are not just stuck with F24 and F36 tubes, F35, F27, F2,F20 and probably all the rest will fit, though I can't say for sure about the rest.

The higher the majority of the holes are on the tube, emulsification begins at lower engine speed,and the lower the majority of the holes, emulsification begins at higher engine speed.

Unfortunately with 8 holes, experimenting willy-nilly can get expensive.

Doug

 

I switched out my 55 idle jets and change them to 52 jets and that solved my low rpm excessive richness and related stumble. After reading the plugs I decided to put in 205 AC jets to lean it out a bit. I Think I found the right combo. It runs great with no flat spots and there's no smell of gasoline nor backfires. Plugs look just right now.
Here is what worked for me:

F24, 140 main, 205 AC & 52 idle

My GT4 now runs better than it ever has (at least while in my possession)!!
I'm going to spend the rest of the day unwinding it around on some twisty road.
I will try to put it on a dyno to get some numbers soon.

Rocco

 

FYI, The Lambo Urraco P300 uses 40 DCNF with F27 tubes.

The US version used 55/ 130/180 idle/main/AC

The Euro version used 55/135/190.

Dunno what diff the F27 tube has vs the F24,and know nothing about the weight,gearing and cam specs on the Lambo motor.

Doug

 

Yes, this may be an option for those building higher CR 308 motors. CR and cam timing go hand in hand.

Doug

 

Here is some more info for you.

The F24 class also includes F26 and F38 F24 and F26 have same number of holes, but I don't know where the hole locations have changed. F38 has several more holes added and is probably for alcohol use. All are same OD at 5MM

The F36 class included F27, F30, F36,F44 and F46. The number sequence is important, as the Etube OD goes from largest to smallest in that order, F27, F30 are 6.2MM, F36 is5.9 MM, F44 is5.5MM, F46 is 3.5MM.. F27 has smaller holes at the top as compared to the F36. I do not know if hole locations on the vertical axis change from one tube to another. The F27 will start emulsifying at a lower engine RPM than the F36, they appear to have the same high RPM emulsification ability.

I will analyze my info further.

I think trying to tune a Weber with the E tubes and mains and air corrector jets all interacting is going to be like trying to herd cats

Doug

 

More emulsion tube info:

Not all E tubes are teh same, even some have teh same F #, but are different.

There are three main series, the 61440, the 61450, and teh 61455.

You can have an F24 in the 61440 series and it is a different length that the F24 in the 61450 series which the DCNF uses.

The DCNF E tubes are 47.5MM long.

The following numbers in the 61450 series will fit the DCNF.

F21
F22

F24
F26
F38

(The F38 is not for alcohol, it will run leaner than the F24 at top end, my earlier post was incorrect)

F25
F28

F27
F30
F36
F44
F46

The breaks between the number designate significant differences in the tube

The first set is not designed to emulsify at higher RPM, it will run very rich at higher RPM

The third set will run even richer down at low RPM than the F24 will.

Doug

 

I would like to get one of each tube and measure the height location of the sets of holes.

I have the number and sizes of the holes for each tube, but no good info on how high up the tube the different sets of holes are.

Knowing exact hole location, would aid greatly in selecting a tube based off an AFR dyno run using a known tube.

Doug