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| Tuning a Weber 45 DCOE setup with Wideband | Rate Topic |
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| Posted: 06-19-2020 10:06 pm |
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1st Post |
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discogodfather Member 
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I thought I would start this thread anew to help guide people with some info on how to interpret wideband 02 sensor readings in a Weber setup (some of it probably applies to Dell's too). My background is: 73 Healey 2.0 Liter high compression with 104 Cams Weber 45's Delta headers and full 2.5" exhaust front to rear, flowmaster 44 Always wanted to run a wideband, after a complete top end rebuild and cam degree'd in just right the engine is running great and starts with minimal drama. My current carb setup is: Emulsion Tube F4 Main Jet 150 Air Corrector 170 Idle Jet 55 F9 Choke 38 Auxiliary Venturi 4.5 Pump Jet 55 Pump Exhaust 40 Stroke Pump Actuator Rod 14mm Float Level 8.5-15mm Never really dealt with a raw wideband reading in terms of a gauge. I used a speedhut unit with a Bosch LSU 4.9, it installed very easy and it's a pleasure to work with the gauge (very low profile). The readings are definitely not what I expected. This is an analog gauge made to look like an old Smiths gauge, and the needle bounces around quite a bit. I know this is now normal, as the gauge has a slight lag with carbs (only about a second) and it's never going to read a straight ratio. Digital gauges mask this phenomenon by updating the numbers which doesn't come off as such a big fluctuation, but the analog gauge really gives you an idea of how volatile the situation always is with internal combustion. You learn to read the flotation and kind of visually average it out to get the best idea of where it is. Some of the readings I am getting currently: Idle = 13-14 to 1 ratio WOT= 8-11 to 1 ratio Cruising at 3500-4000rpm = 12 to 1 ratio Decel (closed throttle) = 15-16 to 1 ratio The idle mixture screw has a DRAMATIC effect on idle mixture is all I can say. Sometimes a 1/4 of a turn yields 1-2 points +/- in ratio. I can easily get anything I like. I have been snooping around the internet to see what people expect to see at WOT and closed throttle. Some say closed throttle should approach 20 to 1, which would mean a max lean condition (most fuel injection computers just shut the system down during closed throttle). Love to hear opinions on this. I am getting popping in the exhaust under hard decel and closed throttle, which seems like it is running too rich. Haven't been able to do some freeway runs yet, just got some of the last exhaust welding done. Will fill in more information as it comes in, I have a feeling I will be finally re-jetting with something other than a hope and a prayer. One thing I can also say is- what amazing people we had in the past tuning these things WITHOUT wideband. Every little turn of a screw makes a difference, and with wideband you can immediately see the results. How did anyone ever tune anything without this! Zen masters or something.
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| Posted: 06-20-2020 03:46 pm |
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2nd Post |
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DonBurns Member
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Thank you for the post. I have not seen much info on this and am very interested. I also notice the big effect from the idle mixture screws. I balance using a CarbTune Pro, and have noticed there is a range of turns of the idle screws that don't have any effect on the CarbTune columns, or how it runs. But they do have an effect on the O2 mixture. What surprised me though was that the idle mixture screws also affect O2 mixture at higher RPM. I thought the "circuits" were separate. So I adjust balance and idle as best I can, Adjust idle mixture by adjusting mixture screws within the range of no effect on balance / column height, and if high RPM too lean or rich turn all four idle screws the same amount to get where I want. I don't have a box with all the jets and tubes. I try to get idle about 13, acceleration tends to go pretty rich, and cruising in the 12's. I suppose the other indicator would be gas mileage. What do you see? Last fill-up was 15 mpg, but there was quite a bit of time running in the garage.
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| Posted: 06-20-2020 10:38 pm |
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3rd Post |
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discogodfather Member
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Fuel mileage will be the last benchmark as soon as some of the popping is sorted out. Power seems great but I need to concentrate on progression. I have a feeling now it is very rich, and I have no doubt the fuel mileage is awful. Like 15 mpg or less.....
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| Posted: 06-21-2020 04:55 pm |
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4th Post |
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Esprit2 Member
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The Weber DCOE Idle Circuit feeds the engine up to 4000 rpm, then hands off to the Main Circuit. So, for most cars with a freeway cruise rpm of less than 4000 rpm, you're cruising on the Idle Circuit. Ignoring the affect of hills... if you're cruising on the Main Circuit, then you're speeding in North America. 4000 rpm is the "Transition Point", it's a function of design, and is built-in to the carb. It is not adjustable. (Similar but different... the Dellorto DHLA Idle Circuit feeds the engine up to 3200 rpm.) Remove the progression hole covers, look in, and you'll see a number of small holes drilled through the wall of the 'tunnel' into the throat. Open & close the throttle, and you can observe the edge of the butterfly sweep past the drilled 'Progression Holes', progressively opening more and more hole area to the flow of fuel into the throat. Some Webers will have as few as two progression holes (very crude, coarse metering), and some Dellortos will have up to six. As the edge of the butterfly sweeps past the holes to the closed-throttle idle position, the last of the progression holes is very nearly (maybe even completely) closed off such that it's not flowing enough fuel into the throat to keep the engine running. But notice that the fuel delivery 'tunnel' continues past the progression holes to the Idle Mixture Screw at the carb's mounting flange end... well beyond the reach of the butterfly's edge. The Idle Mixture Screw is in the last fuel feed hole, not affected by butterfly position, and it's there to provide an adjustable fuel flow into the throat AT IDLE. Being adjustable, it's essentially a secondary throttle for that Closed throttle zone after the butterfly has swept past the last of the progression holes as it closes. The Idle Mixture Screw is only used to adjust the closed-throttle mixture at idle rpm. It is not for adjusting O2 sensor readings at any other rpm! Use your CarbTune to 1) balance the carbs, and then 2) set the idle mixture screws as necessary to produce peak intake manifold vacuum. (Note: you do NOT use the Idle Mixture Screws to BALANCE the carbs!) Make th balance and peak manifold vacuum adjustments at an artifically low idle rpm... as slow as possible consistent with smooth running... no stumbling or misfires. After the Idle Mixture Screws are adjusted for peak manifold vacuum, set the idle rpm back up to 900-1000 rpm. After that, HANDS OFF on the Idle Mixture Screws. If you don't like the O2 sensor's reading at idle, then change the Idle Jet and/or Idle Air Corrector leaner, then re-adjust the Idle Mixture Screw to once again achieve maximum manifold vacuum at slow idle with the new jetting. Adjusting mixture/ O2 sensor readings is a function of replacing jets and air correctors, not turning a screw. And no, it's not convenient. You don't adjust the flow rate thru your lawn sprinklers by turning the fawcet in your bath tub. You don't adjust O2 levels at rpm above closed throttle idle rpm by turning the 'IDLE' Mixture Screws. Installing an O2 sensor does not transcend the need to understand your carbs, and how to tune them. And no, Webers do not have high resolution similar to a fuel injection system with sensors and feedback loops delivering real time status to an ECU. You may think you have a scalpel, but Webers are really more like an axe. Each throat has a replaceable choke, main emulsion tube, main jet, main air corrector, idle jet, idle air corrector. Those are the six playing cards you get to shuffle. And once in, they're not variable... no adjusting screws. And if you choose incorrectly in pursuit of some optimal Air-Fuel ratio/ O2 sensor reading, then you can easily introduce an off-idle hesitation, a lean transition stumble approaching 4000 rpm, or a rich bog-down after 4000 rpm. Regards, Tim Engel Last edited on 06-26-2020 08:40 pm by Esprit2 |
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| Posted: 06-22-2020 12:39 am |
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5th Post |
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discogodfather Member
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Now that vacuum is being mentioned, I have a weird situation: I installed an aftermarket analog mechanical vacuum gauge on the dash. I got a vacuum signal from between the 3/8" rubber tube going to the vacuum booster. It uses a very small 1/16" nylon tube that runs directly to the gauge. When I first turned the engine on, it fluttered so wildly- from 0-24 in hg. Like a full sweep. I thought I had an intake leak or something, but the engine was running so well. Did some reading online and they talked about flutter, and that what you needed to do was put in some kind of restriction to get a clean signal for the gauge. So I first tried to pinch off the nylon tube, and it did get the needle to settle. I installed a little valve meant for a small air compressor and was able to have any level of restriction by turning the knob, and the gauge reads solidly now without any flutter. Problem is, it's reading around 7 inches now? Wondering what this means- maybe the restriction is too tight, or maybe I am getting too close to the vacuum valve on the brake booster? It's about 8" away from it right now. Where is a good place to get a vacuum signal? If I use my EMPI style sync tool (the one shaped like a ball), it always reads around 7-10 kg/h, but clearly the gauge I have is calibrated in inches of mercury. I have read on other forums a 907 should read at around the normal 17-21 inches at idle. Maybe the 104 cams have something to do with it? Lower vacuum at idle because of more overlap? Still, 7 in hg sounds awfully low.
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| Posted: 06-23-2020 03:33 pm |
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6th Post |
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Rick in Miami Member
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A wealth of Weber DCOE tuning information can be found at Keith Franck’s Sidedraft Central Yahoo group. https://groups.yahoo.com/neo/groups/sidedraft_central/info
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| Posted: 06-28-2020 06:03 am |
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7th Post |
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discogodfather Member
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Went from 150's down to 120's and changed from F2 to F4 emulsions and got an amazing result- now the ratios read: Idle = 14-15 to 1 ratio WOT= 10-11 to 1 ratio Cruising at 3500-4000rpm = 13 to 1 ratio Decel (closed throttle) = 16-18 to 1 ratio Running really nice now with minimal popping on decel (just a bit left). Good transition and pulling well in the top rpm's. Going to move to try and rate the high rpm response by fiddling with the air correctors. Took Tim's advice and tuned the idle jets based on max vacuum, and it came out to a 14-15 to 1 ratio so things make sense there. Still a mystery to me why a high compression 2.0 with a 104 like cam is happy with a 120 main jet, it's really bizarre, but I remember when I first got the car 125's were in it and it was running pretty good. From my understanding F3 and F4 emulsions are kind of not really used on sidedrafts too much, which is what the book says. Going to have to research a bit more why these seem to work and the F2's run too rich.
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| Posted: 06-29-2020 09:57 am |
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8th Post |
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discogodfather Member
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I can understand some basics in regards to Webers and Dells in that they have jets, you change them, they basically follow a rich to lean logic. Bigger mains, more fuel. In some cases bigger numbers mean leaner like with air correctors. Never understood the emulsion tube. When you look in the Hammill Book on Webers and Dells, he tells you what most of the internet tells you, that emulsion tubes go from a kind of a rich to lean setup and you should basically start with a tube based on cylinder displacement. That led me to F2's, which ran awfully. Most books and sources seem to say that the other emulsion tubes besides F11, F16, F2, F7, etc. aren't really used and the explanation kind of "trails off". I was just randomly searching on youtube and found this old David Vizzard lecture, and the wool is defintely being pulled from my eyes. In it, he says to turn the emulsion tube upside down and look at the holes on the tube. If there are holes up top towards the main, then your top end is leaned. Middle holes control middle mixture, low holes low end, etc. What a great insight! Armed with that knowledge I started to compare my emulsion tube collection, F2, F3, F4, F16, F7. The tubes that worked the best in my setup was the F4, and low and behold it has holes at the top, middle, and bottom. Seems like this engine likes leaner. Finally some basic things starting to make sense. https://www.youtube.com/watch?v=1pkFSA_rRFI
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| Posted: 07-01-2020 12:13 pm |
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9th Post |
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discogodfather Member
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Finally found a digital copy of a factory weber tuning manual. These are usually very expensive and this is an older version, maybe 1970's. I think the latest one is 1990's era. https://www.lainefamily.com/images/WeberTuningManual.pdf
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| Posted: 07-01-2020 01:49 pm |
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10th Post |
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Rick in Miami Member
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How to Build and Power Tune Weber & Dellorto http://foxed.ca/rx7manual/manuals/carb_book.pdf
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| Posted: 07-06-2020 08:44 am |
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11th Post |
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discogodfather Member
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Did another round of tuning, this time concentrating on transition (4000 and up) and high speed throttle response and high speed ratios, including fast throttle and WOT pulls: in my original setup I had: 38mm chokes 4.5 Aux Venturis 120 main F4 emulsion 170 air 55f9 idles 45 pump jets I went and tried some other combinations: F2 and F16 Emulsions - bad breakups, not smooth progression Tried 50 f11 idle jets - not able to get the engine to run without lots of throttle or using the cold choke. She seems to love 55F9 and won't run well on practically anything else, 3.5 turns for seated on the mixture screws. Around 13.5 to 1 on the wideband after set for max manifold vacuum. She simply loves the F4 emulsion as much as the 55F9 idles. The F4 is a strange emulsion tube, it's listed in some of the books as a racing tube designed for alchohol? Some descriptions seem to suggest it has "fuel and air mixing at all rpm's and keeps fuel in reserve", whatever that means. The tube has holes in all of the areas- top middle and bottom. This is really the only emulsion tube I have which allows for smooth transition. I was still experiencing popping on decel and as soon as I really got my foot into the throttle, doing quick WOT pulls, it was bogging and running very rich, like below 10 to 1 on the WB especially at 4000+. So I decided to go to 36mm chokes to kind of try and get the air moving faster thinking it was related to some large quantities of air and fuel kind of lagging. Funny enough it made little difference and I was back to using the same jetting setup after some substitutions, but now throttle response was a little crisper and transition was better, and no more popping. Hard on throttle or on quick throttle, still running very rich and breaking up. Got to the place where I felt like an even leaner main jet and a leaner pump jet is the way to go, at least to see some differences. I feel like at WOT the ratio should be around 10 to 11 to 1, with a cruising of 13 to 1. Ordered some 110 and 100 mains and 35 pump jets. Last edited on 07-06-2020 08:47 am by discogodfather |
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| Posted: 07-09-2020 05:40 am |
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12th Post |
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discogodfather Member
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Went to some 35 pump jets and this improved WOT and caused less rich on throttle, now in the 11 to 1 range. With 36mm chokes I was not able to really approach anything beyond 6000rpm, or the engine felt "floaty" at those rpms. Decided to try something I had never thought of before - using some 40mm chokes just to compare. I had them rolling around in a box for years and surprisingly, given the same jet setup with the 120 mains and 170 AC's and F4 Emulsions, it runs relatively the same. The higher rpm's feel more approachable now and it's pulling past 6500. But this still seems odd to me given the 104 cams and how this is really supposed to be shinning in the higher RPM's. At a loss to explain the different phenomena: 1) Regardless of setup, she seems to need the 55F9's and the F4 Emulsions to run well at all 2) 120 mains seems so lean, but she still reads rich 3) Regardless of chokes, 36, 38, or 40mm the only difference is higher rpm limit 4) Still kind of a rough transition but then a lack of top end performance in terms of WOT sluggishness and slow response Messed with some timing today, gave it some more advance. Will try the 110 mains in the near future. Good A/F ratio though: Idle 13.5 to 1 Cruise 3000 rpm 13.5 to 1 Cruise 6000 rom 12.5 to 1 WOT 11 to 1 50% throttle 12 to 1
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| Posted: 07-10-2020 05:33 am |
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13th Post |
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discogodfather Member
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Major discovery today- as I was doing my usual swapping of jets and tubes I decided to change back to the 38mm chokes. I have long intake trumpets and since my top end rebuild I had fitted a set of "filter socks". They are just a foam element cut into a little cap like shape and then you simply put them on the trumpet. This time I didn't put them back on, and didn't fit the trumpets on either, just a naked DCOE. I immediately noticed the idle was different and readjusted, then realized my AFR's were completely different. Running her around the AFR's had shot up by 2-3 points and transition was great, and now VOOM- big RPM's pulling very hard up to 7000+. So those awful air socks had really screwed up my tuning. Using F3 emulsion now and she is running very nicely, the best ever really since I got her. Running 125 mains seemed awfully lean given the setup with the 104's and the high compression, and naturally it was way to lean and sneezing without the restricted intake. Went up to 145 mains and now she pulls like a horse in the higher rpm's, but I still feel it's a bit lean. New ratios are: Idle = 13.5 to 1 Light throttle = 14.5 to 1 WOT = 12.5 to 1 Cruising most rpms and loads = 13-14 to 1 Closed throttle - 15-16 to 1 (some popping still) Years ago when she always had this setup (before the wideband): 125 mains 170 air correctors F3 emulsion 55 pump jets I remember Judson telling me years ago that the pump jets seemed really big and the mains a bit small, and I think without the wideband the original setup was fooling us in the sense that the pump jet was hiding some major flaws in the main circuit. I also remember reading Tim Engel's advice on how the pump jet is often diagnosed as a problem when it's really the mains. Too bad that didn't sink in! New setup: 145 mains 170 AC F3 emulsion 45 pump jets Really starting to scream! Transition is a dream with no flat spots or issues, she just blazes through it. Going to try 150 mains and slowly see if I can raise the air correctors up a bit, should help with mileage. FYI those sock puppet filters really suck. I'm working on an airbox with a cold air feed, so may dust off some old K&N filters until I get that system up and running.
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