F16 vs F9 Emulsion tubes

[roy]

What is the difference ? Richer high end ? leaner high end ? More fuel to draw upon ? I have only used F16 on all size engines - am I missing something ?

[101 Alfa Mike]

The Weber Tuning Manual (published by Weber) is a great reference and contains dimensional data on emulsion tubes.

My 1600 came with F16s and I tried some F34s just because I had some on the shelf. They came on a little quicker and, unlike the F16s, gave a flat A/F across the upper rpm range. So much better.

Expect others will disagree, but my theory is Alfa ditched the F16s and went to F9s & F34s in the later cars because they work better.

Mike R

[ECARRILLO]

I have read several Weber books and have not really understood the diference. I think that you can only ultimatley really see a diference in a dyno. I have both F9 and F16 in the tool box. I think that I use F16.
I mention that you can only see a difference in a dyno, because I find it dificult to believe an individual can tell them apart, maybe if they are signifcantly different, but not if they are somewhat alike.
If someone can tell us the diference and educate me, I am all ears!!

[101 Alfa Mike]

There is nothing like a wideband O2 sensor with datalogging capability. The only problem is knowing when to quit and leave well enough alone!

Mike R

[1,6 HF]

Quote:

Originally Posted by ECARRILLO I have read several Weber books and have not really understood the diference. I think that you can only ultimatley really see a diference in a dyno. I have both F9 and F16 in the tool box. I think that I use F16. I mention that you can only see a difference in a dyno, because I find it dificult to believe an individual can tell them apart, maybe if they are signifcantly different, but not if they are somewhat alike. If someone can tell us the diference and educate me, I am all ears!!

[ECARRILLO]

OK, so when do you need to use the F9 and when do you need to use the F16, I notice you also mention the F11, is this similar to the F9.

[1,6 HF]

F11 first: The F11 is the same basic configuration as the F9 except that it has an additional 4 x 100 air holes (F in the diagram) low down, which is for leaning @ high rpm. The F11 is also narrower, with an OD of 8.0, which means that there's more fuel in the emulsion tube well. This means, in general, that the F11 will flow more fuel.

There are basically two factors in emulsion tube selection: OD/ID, and air holes.

OD controls how much fuel is in the emulsion tube well. The smaller the OD, the less fluid it displaces and therefore the more fuel in the well. More isn't always better; it's a function of cylinder displacement and the number of cylinders that each carb barrel is feeding. A 1.6L 4-cylinder with a pair of DCOEs needs to flow less fuel per barrel than a 2.0L with one two-barrel DCNF. ID goes up as OD goes down; the more furl you're flowing, the more air you need.

The air holes vary in location and number--the size is always constant at 100. They occur in pairs, fours, and eights, and they occur higher or lower on the tube. Holes higher up affect lower rpms (again it's all relative: "low" starts @ 3000 rpm), while holes lower down affect higher rpms.

So the answer to your question is that it depends on what's happening with your engine. You need to balance the emulsion tube characteristics with the main jets and the air correctors. What complicates matters is that you can use the mains and air correctors to "correct" for the wrong tube, and vice versa.

Maybe an example will help. When I got my car (1.6L running 40DCOEs w/ 30 chokes), the previous owner was running F11 tubes with 115 mains and 200 airs. The small mains were compensating for the greater amount of fuel in the well (smaller OD), which is just bizarre. And it was running too lean at the top end, because the F11 has the additional "high lean" holes and it was running 200 airs.

I'm now running F9 tubes with 120 mains and 160 airs. The book says that I should be running 170 airs, but it was running too lean high up. Theoretically I could have gotten the same leaning effect with F16s (fewer air holes), but the F16s were too rich down low--I was getting a stumble @ 3500 rpm, at the transition to the main circuit. The pairs of air holes higher up the F9 cured the stumble. Again, I could have cured the stumble by using smaller mains, but that would cut power all through the rev range.

If the F16s are working for you, don't go through the brain damage of changing everything. If you need more fuel flow, and increasing the main jets (the first thing to try) doesn't do enough, or you need to go leaner high, and increasing the air correctors (the first thing to try) doesn't do enough, or you need to go leaner low, then it makes sense to experiment with different tubes, along the lines I sketched out.

But, to paraphrase 101 Alfa Mike, if it ain't broke, don't fix it. And even if you have a rolling road dyno, an O2 sensor, and unlimited time, 90% is close enough IMHO--trying for the extra 10% is just as likely to end you up at 70%.

And that's about all the help I can offer; everything I know is from studying the tech manual and a lot of trial and error--mostly error.

[roy]

So what are people using in their 2L Alfa's ? F9 , F34 or F 16 ?

[alfaparticle]

I think that the F16 was the standard for 1300 and 1600 engines. F9 was the standard for 1750 and 2L engines with the old style carbs. F41 was for 1750s with late type "emissions" carbs and F34 was for 2L cars with emissions carbs.

My first GTV had 40DCOE28's and it gave lousy gas mileage compared with my Spider that has "emissions" Webers. I started to lean out the low and mid range by swapping out idle jets and emulsion tubes. One of the changes that I made was to switch from F9 to F16 and I think that it contributed to improved mpg without adversly affecting the performance. I think that Alfa's were often set up to run rich to eliminate flat spots that are more of a problem with old style points ignitions. That gave Webers a reputation for poor fuel ecconomy. My experience is that electronic ignitions allow you to run leaner mixtures at the low/mid range and get much better gas mileage.

I have 40DCOE116/117's with 34 mm venturis on my Spider. They originally had F41's and 55F17 idle jets. They now have F34's and 55F21's. This engine has Richard Jemison racing camshafts and other mods and it makes a lot of power yet still averages 23 mpg.