AZGhost623 Posted March 29, 2013 Share Posted March 29, 2013 I have an AEM Wideband O2 sensor hooked up. Its reading 11.5 at idle. What should I be at/around on idle? What should I be at say 3000 rpms or so driving down the road? Triple Weber 45's setup with direct ignition (no distributor). Im at about 16 degrees at idle (from what I have read others have setup), and 36 degrees at 3000rpms. Idle RPM is at 1000. Thanks! Quote Link to comment Share on other sites More sharing options...
Kris.Is.Awesome Posted March 30, 2013 Share Posted March 30, 2013 I do not know much about AFR in carb cars, but most everything fuel injected I have worked on, I'm about 14-15.2 at idle. Quote Link to comment Share on other sites More sharing options...
AZGhost623 Posted March 30, 2013 Author Share Posted March 30, 2013 (edited) I found something on the internet earlier that said anywhere between 13 and 14. I was able to get them all adjusted so thats what the meter is showing now. I dont know about EFI vs Carb either, but atleast I have a reference now. I also dropped my timing a bit down to 12 seems to like that a bit better. Edited March 30, 2013 by AZGhost623 Quote Link to comment Share on other sites More sharing options...
duragg Posted March 30, 2013 Share Posted March 30, 2013 AFR on gauges aside, you should still reference the lean best find method and have an idea that all screws take about the same turnage to peak RPM in each cylinder. Takes a while but keep working till all are adjusted by reference to sound or a digital tach for max RPM .from there u may go 1/4 to 1/2 turn out (richer) to get behavior where u want it . A nice collection of jets can be toggled also Drivability trumps AFR reading on a gauge which is a good relative reference tool Quote Link to comment Share on other sites More sharing options...
zguitar71 Posted April 3, 2013 Share Posted April 3, 2013 (edited) With carbs I'm shooting for 12.5:1 and my timming is 18 at idle and 34 by 3000. I ran 36 but that is only with race fuel. I have 10.7:1 compression and I can barley get by with premium on a cool day so I brought it back to 34 and on auto crosses I bump it to 95 octane just to be careful. The dcoes are better with a little richer mix than the optimal 14.5 or so. Edited April 3, 2013 by zguitar71 Quote Link to comment Share on other sites More sharing options...
AZGhost623 Posted April 4, 2013 Author Share Posted April 4, 2013 (edited) Yep, 12.5:1 is what I found out these need to be at from a dcoe pro on another website. I have a good feeling Im somewhere close on my all in at 3000 rpm range, because the car runs pretty good at higher rpms, but lower rpm is where Im struggling with on getting the tune right within the idle circuit which is going to require some jet changes and things I believe.. Ill play with the timing more to see what kind of response I get if I bump it up a bit with some quick blips to see if it works any better. I see your running triple 45's as well. Care to share your specs on the jet sizes and chokes on it? Edited April 4, 2013 by AZGhost623 Quote Link to comment Share on other sites More sharing options...
AZGhost623 Posted April 4, 2013 Author Share Posted April 4, 2013 Just to clear my head a bit, this is pretty tricky... the O2 gauge jumps a bit between 12 and 12.5 which isnt too bad I guess. But when the electric radiator fans come on, it drops below 12. So Im going to err on the high side a bit. How much should it vary? .5 ok? Also when I do a quick rev on the engine after a long idle, the "bar" that attaches to the arms for the throttles doesnt always seem to come back to the same position. I have a old clutch spring to make sure it pops up, but its off a bit that makes it just enough that its not back at 12.5. I think I have had enough exhaust fumes for one night.... Quote Link to comment Share on other sites More sharing options...
zguitar71 Posted April 4, 2013 Share Posted April 4, 2013 I'm using 55 f9s for the idle but might need to go to a 50 or 55 f? And get more air vs less fuel I'm just a little too rich. On the top end I have 145 jets and 195 airs with 36 venturies. I have played with so many combos, all with 36 venturies, I'm not sure of the fuel/air ratio but the top end runs great but I run out of air before cam shaft. I can get small variations in power with more fuel vs air and visa versa but no combo gets past 7k before the power falls off, the cam should pull to 7500 and every time I calculate the Venturi size I get 37 as the best option. But then I have to go through the entire jetting ordeal again and right now I need to sort some other issues on the car that I have put off. I'm going to try and get the carbs exactly as I want them by the end of this summer. Quote Link to comment Share on other sites More sharing options...
zguitar71 Posted April 4, 2013 Share Posted April 4, 2013 If it falls in between 12 and 13 your probably good. The guage usually varies quite a bit. Mostly you do not want any lean or rich spots as you go through the rev range or as you progress through the circuits of the carbs. The a/f meters are great for showing problems that you other wise might not realize are there like leaning out at wot or too rich, they really help in the fine tuning. The stickey linkage can be as trying as the jetting. Mine was great for about a year then started doing the same thing yours is. I readjusted everything so it was as free as possible when it was cold so when everything got hot later and all the metal expands there would not be any binding. So far so good but our weather has not started to be very warm yet..... Quote Link to comment Share on other sites More sharing options...
AZGhost623 Posted April 4, 2013 Author Share Posted April 4, 2013 That's good to know on the gauge that it does move around a bit. I knew what I was getting into when I went to this setup, so I was prepared a bit, but still wasnt prepared enough now that Im knee deep in all this. With summer approaching in AZ I was hoping to get some real good road time, but looks like Ill be back to just resto work and working out the tune over summer. As far as jetting goes, I still have quite a ways to go to get things figured out. My carbs came with a cable linkage setup to use in lieu of the stock mechanical, but I havent figured out how exactly its supposed to install. Ill probably look more into that as well as I heard thats more ideal. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 5, 2013 Share Posted April 5, 2013 What's the point of such a rich idle? I set my DCOEs to 14.5:1. There are really good threads on classiczcars.com about linkage issues, especially if you're running the ubiquitous Cannon manifold. Quote Link to comment Share on other sites More sharing options...
AZGhost623 Posted April 6, 2013 Author Share Posted April 6, 2013 The tuning guide written by DCOE_TUNER on the Yahoo forum you gave me, also lists to have it at 12.5:1. I also found this on a few other websites. I dunno the explanation, but seems to be common from what I have been finding. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 6, 2013 Share Posted April 6, 2013 (edited) A rich idle is a waste of fuel. The only reason I see for this is to cover up lean holes in the progression phase. I think Keith wrote that paper 7-8 years ago, he may have different thoughts presently, especially since he's developed his own jets. EDIT: The paper is a great primer and has plenty of good stuff in it, but a few things need to be updated. Keith is working on a new one, AFAIK. Edited April 6, 2013 by Leon Quote Link to comment Share on other sites More sharing options...
zguitar71 Posted April 7, 2013 Share Posted April 7, 2013 The idle circuit takes the motor to +- 3k so the richness is not just at idle. I agree that it is a waste of fuel if your worried about mpg; however, the 12.5 is for performance not fuel efficiency. The nature of the dcoe carb is to give the best performance at the 12.5 ratio ( or close to that). They can be tuned to a more efficient ratio but I only run them for the performance aspects not the best mpg. Quote Link to comment Share on other sites More sharing options...
Leon Posted April 7, 2013 Share Posted April 7, 2013 The idle circuit takes the motor to +- 3k so the richness is not just at idle. I agree that it is a waste of fuel if your worried about mpg; however, the 12.5 is for performance not fuel efficiency. The nature of the dcoe carb is to give the best performance at the 12.5 ratio ( or close to that). They can be tuned to a more efficient ratio but I only run them for the performance aspects not the best mpg. The idle/progression circuit does go to higher RPM, but only at partial throttle. There is absolutely no good reason to be 12.5:1 at idle or partial throttle. Part throttle means you're cruising and getting good mpg and producing less emissions is (or should be) in your best interests. At WOT, when you want max power, you're using the main circuit which is a whole different ball-game. BTW, it is not "the nature of the DCOE carb to give best performance at 12.5:1". It is the nature of the internal combustion engine, no matter how you're fueling it. I consider mpg a "performance aspect" of my engine. I can see not caring much if it's a pure track car since you'd always be on the mains and at full power, but anything else and it makes zero sense to dump a ton of fuel into your engine when you don't need to. This is the whole point of having multiple circuits in a carburetor. Quote Link to comment Share on other sites More sharing options...
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