More stupid Weber emulsion tube questions

[andrewlandon67]

Sorry in advance for the long post, but this is something that's really been bothering me. I'm running a 1914 (FK-8, 1.4 rockers, 8.75:1, EMPI 40x35.5 CNC wedgeport heads, 1 1/2 merged, 44 HPMX w/36mm vents) and my friend and I tuned it on his wideband not long ago so that it runs really well on hot days, but the jetting spread we figured ended up being quite a bit richer than I've read should be run on F11 emulsion tubes(150/F11/190), and now that nights are cooling down here in Denver, it feel and sounds like my car is starting to lean out a little bit, especially on the transition. The problem I'm running into (in my mind) is that most of the reading I've done says that the F11 emulsion tube really isn't intended to work with anything beyond a 145 main, and that they'll go over-rich at high RPMs with anything smaller than a 200 A.C. jet.

So where I'm going with this is I need either slightly more fuel or slightly less air in my mixture, but where should I go as far as emulsion tubes? Or should I even worry about that? When the air here gets hot the car runs beautifully, but this being Denver, a good 8-9 months out of the year is spent around 65 degrees or lower ambient temp, and I'd really prefer my car to run at its absolute best the majority of the time without the potential of overheating and catastrophically damaging my engine due to a lean condition.

Any help/advice is greatly appreciated, especially since I feel like my engine is sort of in between a mild/moderate street motor displacement and valve size, but a much more aggressive cam and port size and shape. Also keeping in mind, my car is driven 5-6 days a week, with regular trips to the drag strip throughout the year, and gas mileage isn't of the utmost concern.

[Jim Ratto]

Hi Andrew. Do you know which size idle jet you're running now?
Your elevation kind of changes everything, which I'm sure you're aware of.

[andrewlandon67]

The best idle/low transition I've been able to get is with a 60 idle jet, which seems a bit big to me, but the car seems to like it better than a 55.

[Jim Ratto]

I am surprised it's presenting lean issues with that idle jet size, and your elevation.
The F11 tube, in my experience, works best with venturies in 28-32mm range, this isn't set in stone, but in bigger cc engines, with larger venturies, they tend to delay when the main circuit comes in. They are what came from the Weber distributor for 44 IDF Webers when I was selling them in the 1990's, and I think that's still the case. They are also what they screw into the 40IDF with 28mm. I have found the F2 irons out a transition issue that can't be fixed with idle jet, main jet or accelerator pump adjustment. Problem is, emulsion tubes are expensive, when compared to jets and sometimes the difference they make is almost impossible to detect through driving, unless one tube was way off, and you nailed it with your choice on the next tube (my car running F11 is absolutely terrible, compared to F4 I run). You can see it sometimes on wide band. Make sure before you start switching stuff around that all the baseline stuff is covered- valve lash, fresh plugs, ignition parts are good, no vacuum leaks, no issues with plugged idle jets (common on IDF). And make sure floats are exactly right on or there's no way the emulsion tube can do it's job.
You know all that already, but just to remind you.

What symptoms are making you think it's gone lean?

[andrewlandon67]

What's making it seem lean to me is that it's acting like it did before we did the tuning on it, lots of popping out of the exhaust and a fairly large dead spot at the top of the pedal, with the throttle plates hovering somewhere around the progression holes, which would seem like a plugged idle jet except that it idles beautifully. Mostly this has been the past few nights I've been out in it, Denver has been uncharacteristically cool and wet for this time of year and the air has been relatively dense for this area, and once the sun goes down, the temp drops even more, making the air more dense, which to my mind, means it's harder to provide enough fuel for the amount of oxygen the engine is pulling in. I'm not 100% sure if that's what's actually happening, but it makes sense to me. It also seems to not be pulling quite as hard at full throttle up to about 5k which also makes sense as a symptom of the air/fuel ratio being off a bit.

As far as main/air jet sizes go, I have a post of yours from some time ago presenting the four most commonly used emulsion tubes of VW engines, and the part about the F11 says not to use much larger than a 145 main, and not to use smaller than a 200 air jet as that will cause an over-rich condition at high RPM.

Thanks for all the advice, it's greatly appreciated!

[Martin S.]

I thought popping out the exhaust is too rich? Do you have a WB on it still or was that just temporary? that should help clue you in.

[andrewlandon67]

It's just a temporary one that clips into the exhaust. I might try and see if I can borrow it at some point to spend a few nights driving around and see what it tells me.

[Martin S.]

It's a nice gauge to have and not very expensive either. You can see obvious problems like a sudden vacuum leak right away with the mixture changes. I wish someone made one to match my VDO cockpit array. I have the oddball PLX now.

[andrewlandon67]

What size gauge is that? And do you have it just run through a bung welded into the exhaust?

[Martin S.]

It's the same size gauge as the classic VDO ones, 2-1/16" opening in the dash. I bought the PLX when it was a new company about ten years ago. Now they have lots more cool options including a phone app so you don't even need to install a gauge! Mine has the number in the middle, and discrete LEDs around the edge of the gauge going from yellow to green to red. I would like a classic VDO style gauge with an analog needle that swings back and forth if I had a choice though.
You buy a bung and weld it to the collector before the muffler. I've had no problems with mine driving every year, lots of miles and the sensor is still fine.
http://www.plxdevices.com/PLX-Wideband-O2-Air-Fuel-Ratio-Sensor-Modules-Gauges-s/125.htm

[andrewlandon67]

Awesome, thanks for the info! I'll do some hunting and see if I can find one in black, but otherwise it's perfect! I bought one of the Fast-Fab three gauge radio delete panels and I've been wondering what my third gauge should be, that one just might be it! Certainly easier than pulling spark plugs on a hot motor!

[55ragtop]

There's a really great (LONG) read on the samba in the motor/trans forum. Buried in there John Connolly talks about plugging off one or both of the top air bleed holes in F11's. As a test can slide a small piece of welding wire and bend the ends so won't fall out. then solder up if works. From memory this was to help transition issues you're describing. 

[andrewlandon67]

That's very interesting! I've actually thought about doing something to block off just the topmost row of holes, just to see what it would do to the driveability of the car. I think before I go around ruining emulsion tubes I'd still like to try out the F2s like Ratto said. I've been able to tune some of the flat spot out with the idle mixtures, but it seems to be a razor's edge margine before it gets all weird on me again. Of all the reading I've done so far, it really seems like there's not much of something between the F2 and the F11 emulsion tubes, although the only ones people really talk about with VWs are the F2, F4, F7, and F11, so there is certainly a possibility of something out there that's a good in between, I'd just have to hunt for it.

[Jim Ratto]

The primary difference of the F2 and 11 is the difference in the diameter of the two, the F2 being slimmer. The F2 is considered a "high volume" tube, used in conjunction with larger main jets and/or alcohol.
Pick up a copy of John Passinni's book on Webers if you really want a good overview on emulsion tubes.

[55ragtop]

You don't have to ruin any vents by blocking holes with wire as a test.

My motor didn't like he F2's (2332 fk46 comp eliminators and 51.5 IDAs)  F7's were pig rich so I ordered F4's...they have been best so far but still have a split second lean hole at transition from idle to main circ. it's been suggested it may be a poor airspeed issue with the 48mm intake and 45mm vents? I bought bergs grooved Vents to try and help that but have broke a lifter bore out of my case

[andrewlandon67]

Mr. Ratto, do you mean the green tuning book?

[Jim Ratto]

You don't have to ruin any vents by blocking holes with wire as a test.

My motor didn't like he F2's (2332 fk46 comp eliminators and 51.5 IDAs)  F7's were pig rich so I ordered F4's...they have been best so far but still have a split second lean hole at transition from idle to main circ. it's been suggested it may be a poor airspeed issue with the 48mm intake and 45mm vents? I bought bergs grooved Vents to try and help that but have broke a lifter bore out of my case

try a size up on main and make sure float level is per Weber spec. If the float level is off, the emulsion tubes cannot work as they were designed.
My car with new heads presented a slight lean dip in transition and in tip-in, after 2800. At first I suspected issue with accelerator pump output, but I checked and it's supplying spec CC.
Went to 170 main and it came to life. I'm surprised it needed this much main.

Good luck

[Jim Ratto]

Mr. Ratto, do you mean the green tuning book?

The current version is black with yellow lettering on the cover. This edition has good information on emulsion tubes.