pleadingbark Posted November 21, 2011 Share Posted November 21, 2011 Should I presume about 3500rpm is when the main jet kicks in? Quote Link to comment Share on other sites More sharing options...
Leon Posted November 21, 2011 Share Posted November 21, 2011 Should I presume about 3500rpm is when the main jet kicks in? No, test it. This involves finding a safe place to drive the car and removing the e-tubes. Drive it gently until your low-speed circuit can't provide enough fuel. This is where the mains should kick in (at cruise conditions). Keep in mind that you will have very little power so find an empty, open area to test. At WOT, the mains must come in much sooner. This is tested by going WOT in high gear at low rpm. If it lugs, the main is working. If it dies, the main is not providing enough fuel. A wideband O2 sensor is necessary. Check out Keith Franck's "White Paper" at Sidedraft Central. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted November 22, 2011 Share Posted November 22, 2011 Should I presume about 3500rpm is when the main jet kicks in? I agree with Leon that this has to be tested. Here's 2 more cents, too. In my experience the main circuit "takes over" around 2000 (2500 at the highest), which I experimentally defined as "the rpm beyond which putting in a crappy idle jet has no effect." I've never tried it with no e-tubes, I'm curious to perform that test. Air correction circuit "kicks in" around 4500 in my experience. To test this, I put in the worst idle jet I had, and compared the feel of the car to the behavior experienced with the best idle jet I had. Where the car begins to feel the same is the point that the idle circuit is no longer being utilized. Six one way, half dozen the other? Perhaps. Experimentally determining where a circuit "kicks in" is difficult, because by design the circuits either transition from one to the other (idle->main) or overlap (main+air). Quote Link to comment Share on other sites More sharing options...
duragg Posted November 22, 2011 Share Posted November 22, 2011 So I am befelled with an interesting "problem" in that my Onboard panel-mounted Wideband O2 is dying. Perhaps from running 50/50 leaded 100LL fuel. So Now my crutch is removed and I am back to tuning on the Butt-Dyno which I am begining to feel more fond of. With the Wideband I am hampered by feelings of guilt and shame when I discover my very best idle is 11.5AFR. The experts say this is too rich so I "fix it" and it runs worse, barking and popping. I find my best power and feel at a certain AFR that the experts say is incorrect. Yet my "incorrect" AFR is the one that runs best and pulls clean to 7500RPM. The motor just seems to LOVE this setup and the 50/50 mix of 100LL so I am going to let the dead wideband sleep for a while until I really need it to solve a problem. ZRedBaron and others have said this very truth for a while and I am coming back full circle to agree. However, I could never have gotten here with out it. Quote Link to comment Share on other sites More sharing options...
duragg Posted November 22, 2011 Share Posted November 22, 2011 With respect to testing main jet start. I found it a bit tricky. Drove around without the main stacks installed and the initiation point is not at one static rpm. In fact you can milk the idle and progression up to 5000rpm or more. But getting to a definitive Mains Begin Here: XXXXrpm point is pretty elusive for me. I know on my car it is somewhere around 1500 to 2500 depending on throttle position. Butterflys have to physically be moved beyond the progression ports to be sure you are seeing purely main input. You can watch all of this like clockwork on the wideband. Float level was a major contributor to my main initiation. Presently 1 or 2 of my floats are a bit too high and I see fuel flow fluctuations on turning. Thankfully I live in Phoenix now. For me the solution will be to lower the float level which will delay the mains slightly. But increase the progression flow to get them to meet nicely. In the meantime I just try to keep the throttle full open as much as possible. And MAN! Fuel flow at max power is impressive! Not an economy setup. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted November 22, 2011 Share Posted November 22, 2011 So I am befelled with an interesting "problem" in that my Onboard panel-mounted Wideband O2 is dying. Perhaps from running 50/50 leaded 100LL fuel. Correct, O2 sensors do not like leaded fuel. I do not recommend using AvGas... the flame front propagation is deliberately engineered to be slow; it is designed for constant RPM conditions with very cold air *at altitude.* Even if running the car in the Rockies, I do not recommend it. If you were to replace that 100 octane fuel with any other 100 octane fuel, your results would be *much* better in terms of throttle response, power output and fuel economy. Quote Link to comment Share on other sites More sharing options...
bradyzq Posted November 22, 2011 Share Posted November 22, 2011 No, test it. This involves finding a safe place to drive the car and removing the e-tubes. Drive it gently until your low-speed circuit can't provide enough fuel. This is where the mains should kick in (at cruise conditions). Keep in mind that you will have very little power so find an empty, open area to test. At WOT, the mains must come in much sooner. This is tested by going WOT in high gear at low rpm. If it lugs, the main is working. If it dies, the main is not providing enough fuel. A wideband O2 sensor is necessary. Check out Keith Franck's "White Paper" at Sidedraft Central. I find this method perplexing. The emulsion tubes' job is control the onset of the mains. How can one test the onset point by removing the very part that is designed to control it? It seems to me that the test you describe simply tells you how far you can get on idle and progression only. It won't tell you when, how much, and how quickly the mains come on. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 22, 2011 Share Posted November 22, 2011 Correct, O2 sensors do not like leaded fuel. I do not recommend using AvGas... the flame front propagation is deliberately engineered to be slow; it is designed for constant RPM conditions with very cold air *at altitude.* Even if running the car in the Rockies, I do not recommend it. If you were to replace that 100 octane fuel with any other 100 octane fuel, your results would be *much* better in terms of throttle response, power output and fuel economy. "Low lead" isn't that low. FWIW, I have run tanks of AvGas and Trick racing gas (both mixed with pump gas) back to back, and I couldn't tell the difference. Wasn't testing fuel economy though. Seat of the pants tells me that both made more power than the Xylene/Tolulene/Mineral Spirits/ATF homebrew octane boosters that I tried. Quote Link to comment Share on other sites More sharing options...
Leon Posted November 22, 2011 Share Posted November 22, 2011 I find this method perplexing. The emulsion tubes' job is control the onset of the mains. How can one test the onset point by removing the very part that is designed to control it? It seems to me that the test you describe simply tells you how far you can get on idle and progression only. It won't tell you when, how much, and how quickly the mains come on. You are isolating the idle/progression circuit by reomving the e-tubes. Taking the mains out of the equation is the whole point. Driving without e-tubes will show you the idle/progression circuit's true contribution. Put the e-tubes back in and see where the main circuit affects the AFR. Quote Link to comment Share on other sites More sharing options...
bradyzq Posted November 22, 2011 Share Posted November 22, 2011 (edited) You are isolating the idle/progression circuit by reomving the e-tubes. Taking the mains out of the equation is the whole point. Driving without e-tubes will show you the idle/progression circuit's true contribution. Put the e-tubes back in and see where the main circuit affects the AFR. You said "idle/progression circuit's true contribution." I said "how far you can get on idle and progression only." Pretty much the same thing. Basically, I guess I'm saying that if there was a vote to cast, I would vote for zredbaron's method. Edited November 22, 2011 by bradyzq Quote Link to comment Share on other sites More sharing options...
duragg Posted November 23, 2011 Share Posted November 23, 2011 "Low lead" isn't that low. FWIW, I have run tanks of AvGas and Trick racing gas (both mixed with pump gas) back to back, and I couldn't tell the difference. Wasn't testing fuel economy though. Seat of the pants tells me that both made more power than the Xylene/Tolulene/Mineral Spirits/ATF homebrew octane boosters that I tried. Agree on this one. We run 100LL in the airplanes at lots of different RPMS from 2000 to 4500 and Sea Level to 25000'. Its stable over time, smells good and I have access to it at half the cost of Race Gas. At some point you gotta run what ya got. Its better than AZ pump gas is for sure. Quote Link to comment Share on other sites More sharing options...
Leon Posted November 23, 2011 Share Posted November 23, 2011 You said "idle/progression circuit's true contribution." I said "how far you can get on idle and progression only." Pretty much the same thing. Basically, I guess I'm saying that if there was a vote to cast, I would vote for zredbaron's method. I am simply reiterating a small part of what I have learned from Keith Franck's research, as it related to the question of main jet tip-in. He is a retired LBNL engineer who has put in an immense amount of time into actually reverse-engineering the DCOE carburettor to the point of making better idle-jets and emulsion tubes. I have already referred to his Yahoo group, "Sidedraft Central". Read the "White Paper" in the Files section, and maybe then "cast your vote". Quote Link to comment Share on other sites More sharing options...
duragg Posted November 24, 2011 Share Posted November 24, 2011 I found more value knowing where progression ends than where mains begin. End of progression is a constant: x% of throttle position and the butterflies are past the last progression hole and their fuel contribution is gone instantly. Begin of mains is variable depending on rpm, throttle position, instantaneous float level, setup and 238 other things. Off idle was an easy fix. The transition to mains a little trickier but for me the solution will be the same. Get the idle and main jets setup properly and modify the progression holes to suit the car. Quote Link to comment Share on other sites More sharing options...
bradyzq Posted November 24, 2011 Share Posted November 24, 2011 I am simply reiterating a small part of what I have learned from Keith Franck's research, as it related to the question of main jet tip-in. He is a retired LBNL engineer who has put in an immense amount of time into actually reverse-engineering the DCOE carburettor to the point of making better idle-jets and emulsion tubes. I have already referred to his Yahoo group, "Sidedraft Central". Read the "White Paper" in the Files section, and maybe then "cast your vote". Thanks for the info about Sidedraft Central. I joined (though I had to sell my soul to Yahoo in the process) and read the White Paper. It was very enlightening. The e-tube removal test doesn't test when the mains kick in. It shows when they NEED to kick in. Whether they actually do kick in or not is dependent on the setup, and is tested by the WOT test at low RPM you mentioned. You must have to floor (with e-tubes back in) it at about 1200RPM in at least 3rd, probably 4th. Not many Webers are set up well enough to do that with no spitting! You'd have to lug it long enough for the accelerator pump contribution to dissipate. I'm scared to think how my setup would fare in these tests. Quote Link to comment Share on other sites More sharing options...
bradyzq Posted November 24, 2011 Share Posted November 24, 2011 I reread Leon's recent posts, my replies, the White Paper, and I owe you an apology. I for some reason was focusing only on the first test, and not the two together, as you and Keith Franck intended it. Perform both tests and you will have a valid read on the situation. Sorry I made your life a bit more difficult than it need be! Quote Link to comment Share on other sites More sharing options...
Leon Posted November 24, 2011 Share Posted November 24, 2011 I reread Leon's recent posts, my replies, the White Paper, and I owe you an apology. I for some reason was focusing only on the first test, and not the two together, as you and Keith Franck intended it. Perform both tests and you will have a valid read on the situation. Sorry I made your life a bit more difficult than it need be! That's okay, I'm very glad that you took the time to actually use the resource! I've been following Keith's work with a lot of interest, as he seems to be able to make DCOEs run like fuel injection. He does this by gaining a thorough understanding of each function, not hearsay and "formulas" which seem to be the MO in setting up carbs. However, don't give me any credit for his research, I'm just reiterating what I've learned by following his developments! Quote Link to comment Share on other sites More sharing options...
Lazeum Posted December 12, 2011 Share Posted December 12, 2011 (edited) Just to let you know, thanks to this thread and the community, I've learned a lot over the years This past weekend, I was helping a friend who was having a 280zx running rough with triples. Car was hesitating at low rpm, some backfire at carbs at idle and pops during low accels. There was some power but the car was lazy at high rpm. Car has also be tuned up with 55f9 idle jet in the past but it was running to rich and has been rejected from the MOT equivalant test here in Europe. Setup for what is worth was a stock L28 (N42 or F54? - I don't know), N42 head, dish pistons, stock EFI ignition, 40 DCOE, header & exhaust Carbs specifically were running with: 35mm chokes 150 main 190 air 50f8 idle We've plugged the wideband, we found out car was running super lean below 2500rpm and quite rich above. Exhaust is having a leak due to one stud being broken (the closest one from the firewall next to piston #6), AFR curves shown below are probably leaner than they really are. Owner is also well educated & knowledgeable about DCOE's also but he does not have the tool, the wideband sensor. We've shared on jets library for the tuning process, so we had a lot of parts to play with. It was great also to share thoughts about carbs since both of us know how DCOE works. Main jets were 150 units, we went to 145, then 140 to finish with 135. Car run better & better until 135 jets which did not make any improvements, so we came back to 140 which provided the best results from a butt feeling standpoint.. Idle jets were 50f8 so we've exchanged them with 50f9 (air hole went from 1,20mm to 1,00mm), after 10 minutes to retune idle, the car was running smooth, progression was almost perfect. We could hit the throttle above 3000rpm without second guessing about motor behavior. Screws are all around 1 to 1,25 turn from being closed. After a full day, the car was running strong up to the red line with great transition. This tuning process could have probably gone further by messing around with air jets a little bigger, idle jet smaller to make sure 50f9 would be the right ones. I believe exhaust leak should be addressed first also. Overall iIt was a very rewarding experience - first time I was tuning DCOE from someone else car Edited December 12, 2011 by Lazeum Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted December 13, 2011 Share Posted December 13, 2011 BTW, the idle and progression ports never really "shut off", they just become less of a factor as load increases. They are however, still a viable factor at all rpms, especially at lower loads. Quote Link to comment Share on other sites More sharing options...
duragg Posted December 13, 2011 Share Posted December 13, 2011 BTW, the idle and progression ports never really "shut off", they just become less of a factor as load increases. They are however, still a viable factor at all rpms, especially at lower loads. Thats for sure. You really can't link the fuel source (idle, prog, trans, main) to RPM. Or to throttle position or load for that matter. Its really a blending combination of throttle position and airflow (RPM). Follow the airflow and reference the butterfly position and you know who is doing what. Tricky little 'tards. Quote Link to comment Share on other sites More sharing options...
duragg Posted December 18, 2011 Share Posted December 18, 2011 What is the flow difference between: DCOE40 with 36mm choke DCOE45 with 36mm choke? Same choke size, different body size. Will the perform identically in general? Quote Link to comment Share on other sites More sharing options...
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