I have a Crane xr700 optical ignition triggering two Mallory 3a high energy inductive systems which is not a CD ignition so I cannot say how to make an LM-1 operate with a CD system. I run about the same gap you do and it pulls well at all rpm. It sounds like you want to bring the mains in a little earlier to help smooth out that stumble a bit. 140 main jets would certainly do the trick. I tried the 140 main and 190 a/c combo as the other poster has but my plugs were still white as a ghost after a WOT check, so I tried 170 a/c and so far they have been great although I have yet to check on a a/f meter. I checked for air leaks quite a bit last night and have found none. I get all my carb stuff from the fellow in Italy who sells jets on ebay. I cannot recall his screen name but he is not terribly difficult to find and his service is fantastic. I sent him a message about a week ago and he said he had a few F24 available.
What happens when you raise or lower the float level a couple of mm? (assuming all are equal at all times, of course)
My very inexperienced guess would be that the effect would be to slightlyraise/lower the ease of fuel pull over by the venturi vacuum. I really don't have a feel for how much, or at what throttle opening this would occurr. We need a realy experienced carb guy to shed a bit of light. always hopefull, chris
Thanks John, I will go back to the 40's and earlier today, ordered a set of F-24s and 190 ACs from Pierce, because they had them in stock and i have had great advice from them previously. They finally had them in stock, (but for something like $27 each x8 ? ouch). Looking forward to a bit of carb work on the track, or maybe before if i can get the time and open road. Based n SNJ's massivly thorough carb work and operating under the assumption that pre smog stuff was probably engineered to really work, rather than minimally comply with a bunch of bull **** smog -mickey mouse, last minute adjsutments, ie F36 and 125 mains, i am trying the F-24s. VIVA ENZO, chris
While not an expert, here are some amateur observations on our most common dcnf ets. First, lets remember that the fuel flows through the main jet into the inside of the et, then out into the well, from which it is sucked into the aux venturi. While you can intuitively see that number and height of holes in the ET meter fuel flow, less obvious and I believe very important are the relative diameters of the tubes, controlling the volume of fuel you have in the well -- the fuel 'instantly' available for increases in vacuum when we open the throttle. As you can see, the F24 is narrower, allowing more gas in the well immediately available for increases in vacuum. As we know, you cannot take one parameter by itself so much as then the available flow through the holes and jets also modulates this response. F24 4.0 mm external diameter F36 4.5 mm external diameter In addition from the photo, you can see a big difference in the holes. So, being VERY oversimplified, I personally find the F24s are easier to tune for a better throttle response. I find that F24s allow the main circuit to respond faster so it is easier to tune out any transition problems as well as having a brisker throttle response. They are also arguably more tolerant of modern crap gas for similar reasons we have discussed ad nauseum. Would love to hear other's experience with ET tubes; don't believe some folks who say they do not make a difference - they do. best to all Image Unavailable, Please Login
For the same size mains and A/c the F24 gives a richer mixture and eliminates the idle/main stumble, in my experience.
More gas available to suck in the emulsion well May run slightly richer Some folks do this to band-aid the leaness in a sharp corner
Exactly - more gas available (capacitance) when you go through transition and much larger flow holes lessening resistance to flow for the same amount of suck.
Think of emulsion tubes as a way to alter the engine's personality... How's that Russ for surmising many years of Weber tuning experience? LOL! David P.S. Anyone got the specs on a F26 emulsion tube....and a suitable "fatter mid-range/transition" replacement?
my book shows an F26 is used in 3bbl IDF IDA carbs; An F26, 61440 .151 has an external diameter of 4.5 mm, first(lowest) hole is 1 x 100, next up is 2x 100, then 4 x 140 and 4x100 on top this suggests an et for upper band power and richness An F5, 61440.182, has a diameter of 4.25 with 4 x 100, 4 x 100, 4 x 140, 4 x 100 The F5 would give you more well volume, and the increase in lower holes will **in theory** enrichen you at transition and lower rpms. Another good choice would be an idf/ida F24 (different from the DCNF F24), part number 61440.213 with a diameter of 4mm and holes, bottom to top: 2 x 100, 4 x 100, 4 x 140, and4 x 100. This would be the one I would try first, as it is only a little richer with the low end holes, yet has a larger well volume for transition. If this didn't work, I'd try the F5 61440.182 A correction to my earlier post, the F24 for a DCNF, 61450.224 has an external diameter of 5 mm, and the DCNF F36, 61450.232 has a diameter of 5.9mm. Same concepts apply. Anyone still awake???????
Still awake? Actually, I just got up...Thanks Russ! As these tubes are out of my BB, the specs make sense. Once the weather breaks here...and I can get some other cars "in for TLC" down the road, I'll verify my suspicions on the BB with the LM-2. David
Just so everyone knows the source, these part number and specs are from the Pierce Manifolds Weber tuning manual, still available from them. It's interesting to watch how the FChat carb discussions have gone over the years from simply talking about upping main jets to now tweaking emulsion tubes. Mike Pierce would be amazed at us.
So true...I haven't changed, or even thought about emulsions tubes since my old "Alfa/Lotus DCOE" tuning days. And that was a long time ago! David
Since we all talk about the DCNF F24 61450.224 and the DCNF F36 61450.232, let's actually compare them numberwise in addition to the previously posted side-by-side photos F24 61450.224 has a diameter of 5mm, with hole pattern (starting from the top) 4 x 150, none, 4 x 150, none, 4 x 200 (bottom) F36 61450.232 has a 5.9mm diameter with hole pattern (from top): none, 2 x 140, 2 x 115, 2 x 115, none, 4 x 150 (bottom) So, in addition to the larger well volume, the F24 is a lot richer, especially near transition at the lower holes which is why it is way easier to tune that area. We also see the F24 massively richer at the top end as well. **Amateur assessment**: To me, it makes sense that the F24 was more tuned for power, while the more gradually metered F36 allowed for better control for emissions testing. Looking back at my A/F curves, I am thinking the relative lean dip around 4000 may be due to the hole pattern of the F24, even though I have excellent transition and top end mixture curves. So, in summary, if you are still concerned with testing, would keep the F36. For power and a nice transition, would definitely switch to F24s as was the original Ferrari engine specification. I realize that the et is just one part of a more complex inter-relation, but this does help to select the engine's personality and break some of the 'et mystery'. All comments and discussion welcome, as I am also still learning.
It's mostly because of you, ya carb nerd! I have learned much from your carby posts, oh great carbmaster Russ!
OK, here is some info I have put together to add to Russ's words. You'll get the general Picture. Here attached is a list of the Emulsion tubes available. I have highlighted three tubes. The first two are the ones we know. The F36 and the F24. We all have one or the other it would seem. I have F36's but with P6 cams, Borgo's and 36mm venturi. This is how the car came to me. This week I will get it finally on the dyno to see what it is doing. It does go like a rocket, but yes it has that stumble around 2600 rpm. The general consensus would be that this combo of pistons, cams and venturi would certainly steer me towards the F24's. Most likley this is what I will do. Keep in mind here that I have the car for the track, so pottering around @ 2000rpm is not what I am concerned with. For the record though (hesitation @ 2600rpm aside) the car starts like a dream, idles beautifully (I can get it to idle reliably @ 600rpm) and does accelerate just fine around the streets but then goes like a firecracker past 3000rpm. After Russ's suggestions I should be able to correct the stumble with some careful carb jet changes. The interesting part is the third ET, the F6. This is the tube used on the Le Mans car. Check out the number of holes this sucker has! Bizarre though it has quite a wide diameter compared to the others (8.3mm on the F6 compared to 5mm on the F24) that would suggest that it doesn't allow as much fuel to sit in the well. Considering the dyno this week and the most likely scenario of going to F24's, I have to tell you that I am tempted to also try a set of F6's just as an experiment. Order some F24's, go back in a couple of weeks and run it on the dyno with the F24's and log it and then put in a set of F6's and see what happens. What do you reckon? Steve Image Unavailable, Please Login
Terrific information!!! If the volume in the well has to do some with transition the the wide F6 makes sense -- you are wee concerned with low end transition blowing down the Mulsanne at absolute top speed for 24 hours. I think this does bring up something to look at the tubes comparatively. The bottom holes (G,H) are the ones primarily feeding fuel into the well. In the F6 and F36 the upper holes feed air from the air correction jet; the F24 has a small passage all the way through, but the idea is the same. So as I am learning about ETs, I look at: 1. diameter -- volume in the well for transition 2. bottom hole -- ease of getting gas in the well 3. upper holes -- determine the ranges sensitive to the air correction jet The aux venturi is sucking fuel through the main jet and air throgh the air corrector (which acts as a 'brake' modulating on the suction); these all mix in the well before being sucked out into the aux venturi (we've covered the sizing of these before, but the 4.5s we all use are tall to allow for steadier vacuum signal less affected by reversion waves) cool stuff. russ "be the carb"
GREAT info. I had an inkling of an idea how the ETs work but this is beginning to clear away the fog.
Just received a set of F-24s and 190 ACs from Pierce. Hope i have a bit of time to try them out before doing Thunderhill on the 17th. Russ, Did you ever find a work around for the rpm sensor addition to the LM-1? I haven't tried it yet, because i heard there were issues with the rpm unit and the MSD. Any suggestions??? Just in a tizzy. chris ;-)
What about the progression holes drilled in the throat? More specifically, doesn't the order and size of these affect the part-throttle and transition from idle (but not WOT) as much as just about anything else (including the etube)?? I haven't studies my weber manuals nor done any weber tuning in a few years so my recollection may be rusty....
I used the tach signal generator off the MSD with an LM-2 - heres a sample graph showing rpm and aggregate A/F: Image Unavailable, Please Login
Yes - the transition characteristics of the idle circuit are metered by the idle jet and progression holes, and the transition characteristics of the main circuit are determined by the main jet, et, and to a small degree the a/c (a/c used usually at high rpm tuning). Although some folks drill new holes for the progression transition, but I have found you can tweek the upper side of it (main circuit) enough to where drilling the rare body casting is unneccesary.
