PandaZ Posted November 29, 2009 Share Posted November 29, 2009 It doesnt look like anyone has mentioned needle & seats yet! This should'nt be overlooked, in setting up your carbs. In my L18 i was using a 296º dur., 78º overlap, .5" lift cam, 46mm/38mm valves with 11.5:1 comp and 42mm dcoe's modded to fit big chokes, essentially 45's, (setup was originally on a L16 bottom end) and i was running the bowls dry on high speed runs! I eventually had custom sized n&s's made (cant remember the actual size though, sorry) to releave this problem (next step would be to extend the bowls), this simple change netted me an extra ~30kmh (based on tacho, as was well off speedo)! Quote Link to comment Share on other sites More sharing options...
Lazeum Posted November 30, 2009 Share Posted November 30, 2009 If you're talking about the needle valve, I've made some trials in the past with mine. I went from 175 needle valve to 200. I've seen some changes, those might have an impact on carbs behavior. i said "might" since I don't know for sure if the impact is due to the valves or because of gas management system (mechanical fuel pump with regulator - since I also have a unplugged electrical pump - a noisy Carter unit) Are you sure your problems did not come from a pump not big enough to supply the correct fuel quantity? Quote Link to comment Share on other sites More sharing options...
PandaZ Posted November 30, 2009 Share Posted November 30, 2009 Yes, needle valves, thats some good work there Matt, missed that post when i was reading through. It was entirely possible there were other problems at play, back then i was tuning by the seat of my pants. I was using bp100 fuel, which may have complicated things for me. The idle and low rpm suffered alittle with the change, with a noticable float rock, loping increase at idle, which tended to cause fouling issues if left idling for too long, but at high rpm in 5th seemed to make a very good improvement. I assumed it was float bowl related due to the engine leaning up (kill plug checks) at max speed and not pulling, then backing off throttle slightly and pushing again increased rpm then fell off shortly after (possible throttle jet assist)?! Well it made an improvement for me, so i took the small victory over the Weber demons! lol Also it was interesting to see the AFR readout of your needle valve experiment, showing what effect it actually had. Thanks. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted November 30, 2009 Share Posted November 30, 2009 I would check the fuel pump... however, what you've done sounds logical to me to fix the issue. However, we did not have the issue you've here and some of us have high HP output engine too with no needle valve issue I'm aware of. Regarding your fooling issue at idle, you might want to try one step hotter plugs if you haven't done it already Beware of knock but it might do the trick. btw, you definitely need a wideband: that's a amazing tool to tune your engine! Quote Link to comment Share on other sites More sharing options...
Guest Flauski Posted February 22, 2010 Share Posted February 22, 2010 wow , thats some serious knowledge in this post. Didnt see anything on Dellorto 40s, can they run the same specs as the webers? Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted February 22, 2010 Share Posted February 22, 2010 wow , thats some serious knowledge in this post. Didnt see anything on Dellorto 40s, can they run the same specs as the webers? The theory of operation is the same, the tuning procedures are the same, but the actual parts used will be different. I would suggest you get the book "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors" Quote Link to comment Share on other sites More sharing options...
NismoZ Posted February 28, 2010 Share Posted February 28, 2010 Make sure all your vacuum port plugs are TIGHT...the 6 grey ones and the blue one...use zip ties if you have to http://forums.hybridz.org/index.php?/topic/89120-twm-intake-manifold-issues/ Dtsnlvrs, Carbs are tuned with 32 chokes, 57 idle jets, 132 main jets, 180 air correction jets, 38 pump jet and #11 emulsion tube with 5 progression holes. Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted February 28, 2010 Share Posted February 28, 2010 http://forums.hybrid...anifold-issues/ Dtsnlvrs, Carbs are tuned with 32 chokes, 57 idle jets, 132 main jets, 180 air correction jets, 38 pump jet and #11 emulsion tube with 5 progression holes. Well, the handy calculator program carb thingy says....130mains, 180 airs, and a 50/7850.2 idle....I would compare that to what the speedpro book says for lean / rich in the idle emulsion and go fro there.....I dont know the delorto numbering system off the top of my head....but you should be "close" with what you have....at least close enough to get it running and on a dyno Quote Link to comment Share on other sites More sharing options...
Dtsnlvrs Posted February 28, 2010 Share Posted February 28, 2010 It doesnt look like anyone has mentioned needle & seats yet! This should'nt be overlooked, in setting up your carbs. In my L18 i was using a 296º dur., 78º overlap, .5" lift cam, 46mm/38mm valves with 11.5:1 comp and 42mm dcoe's modded to fit big chokes, essentially 45's, (setup was originally on a L16 bottom end) and i was running the bowls dry on high speed runs! I eventually had custom sized n&s's made (cant remember the actual size though, sorry) to releave this problem (next step would be to extend the bowls), this simple change netted me an extra ~30kmh (based on tacho, as was well off speedo)! Yeah, we discussed it quite a bit, and have determined that the 1.75's "the book" recomends is way too small....every car with similar single cylinder displacement to our Z's that weber put DCOE's on had 2.00 needle valves . I would venture to say, that someone with a 3.1L and any kinda cam should be using 2.25's Quote Link to comment Share on other sites More sharing options...
NismoZ Posted February 28, 2010 Share Posted February 28, 2010 Well, the handy calculator program carb thingy says....130mains, 180 airs, and a 50/7850.2 idle....I would compare that to what the speedpro book says for lean / rich in the idle emulsion and go fro there.....I dont know the delorto numbering system off the top of my head....but you should be "close" with what you have....at least close enough to get it running and on a dyno Got a problem, I cant use the 7850.2 idle jet holders on the emission type carbs, it would be useless according to Alfa... Quote Link to comment Share on other sites More sharing options...
Lazeum Posted March 30, 2010 Share Posted March 30, 2010 (edited) I'm in process of swapping my old stock N42 head with Schneider cam with Braap P79 "street" tuned head and Rebello cam  (car should start next Weekend!!!) Since the carbs were out, I wanted to check float level, linkage, jets, etc. I'll have to tune again almost from scratch my carbs and I found out my accel piston (in red circle in picture attached) is not at the same height on every carbs. Does anybody know how to sort that out? Since I will redo the whole tuning process, hopefully I'll be able to learn a little more again about those. It will be soon time to get some more jets If Mark is reading, I believe after a lot of reading the rich point in the AFR curve could be linked with pulse in the intake (my setup is Cannon manifold, DCOEs & roughtly 2" air horns). One way to check it would be with different or no air horn (but something would have to hold the chokes in place during the test. I've also learn that having a solid plate close to the air horn (K&N style air filters) could also help getting more power. In some specific case, I will not be a restriction but more like a mirror that could help with pulses. this theory might need some investigations.... Edited March 30, 2010 by Lazeum Quote Link to comment Share on other sites More sharing options...
yetterben Posted April 7, 2010 Share Posted April 7, 2010 Anyone have any extra air correctors they wanna sell. I picked up a set of 190's to richen up the top end around 4 grand i start to rise into the high 13's. They have not gotten here yet so i am trying to cover some bases and see if there is any of you guys that have some to get rid of. Quote Link to comment Share on other sites More sharing options...
NismoZ Posted April 9, 2010 Share Posted April 9, 2010 Anybody got some dellorto jets they want to sell? I need idles and mains.. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted April 25, 2010 Share Posted April 25, 2010 (edited) If Mark is reading, I believe after a lot of reading the rich point in the AFR curve could be linked with pulse in the intake (my setup is Cannon manifold, DCOEs & roughtly 2" air horns). One way to check it would be with different or no air horn (but something would have to hold the chokes in place during the test. I've also learn that having a solid plate close to the air horn (K&N style air filters) could also help getting more power. In some specific case, I will not be a restriction but more like a mirror that could help with pulses. this theory might need some investigations.... by "pulse" i assume you mean the low pressure transient from the piston moving downward and pulling fresh air and fuel through the intake? then yes, i still agree with you that this is the problem. i'm still firm with my belief that my flat spot can't be fixed, which is actually a function of such a radical camshaft and overbored engine meeting a carburetor. a carburetor is a manual throttle in every sense. nothing is metered unless YOU (the tuner) made it that way. the only thing you can do is change the air (temperature, elevation, humidity, etc) and literally the accellerator pedal with your foot as you drive. those are your only inputs for the driver. in a normal street car with a carburetor of any kind, mashing more pedal produces more fuel in very carefully designed and metered proportions. it works quite well. in our high-performance 3.1s, everything is bigger. bigger pistons, bigger stroke, bigger cams, bigger valves, bigger venturis, bigger jets, bigger spark, better fuel. its all proportional, it *should* work, but it doesn't. i'm not saying carbs don't work on race cars. they do. just not a 1 carb per cyl setup AND big slugs. formula 1 cars used to use side drafts. i've seen a maserati F1 car in a museum with weber DCOEs, in fact. point being, it was a small displacement / many cylinder (usually 8) setup. big block chevys use common plenum intakes -- one massive carburetor in the middle of all 8 cyls. either way, fast flow through small holes. the reason i'm stymied is that when you widen everything for flow, the velocity of the fluid (air + fuel) decreases. period. now put in a cam that idles at about 1450 rpm, and the carburetor is experiencing a very rough pulse as it sucks in a large volume of air at a slow speed intermittently (giving it that rough, pissed off sound, because in reality it's running like $h!t). i think i might try dropping down my venturis again. i'm at 36mm at the moment. might try 32 even. real world, we all subscribe to this thread because in some aspect, we feel we should be able to floor the gas pedal at a certain rpm and the engine should not chug or fall flat on it's face, but smoothly sing through the power band. the carburetor works on pressure differences, ideally expecting smooth pressure transitions, and when the engine inputs aren't smooth in terms of rate of change of fuel mixture (ie pedal position), then the engine struggles. enter the driver. that's also what makes driving carbureted cars so fun: we, as drivers, have to know our car to get the most out of it. ideally it also helps you be a smooth driver, too. that said, sure, there's always something new that can be tried to lessen the dead spot. any reports on experimenting with the stacks, matt? let me know if you took your stacks off and had better throttle response in that dead range. i have air stacks installed as well (inside my cold air box). these pics are from my rebuild in '08: i'm schwagging this based solely off tinkering with webers and different engine setups over the years, but if i wanted to target the engine that might make the most of the webers without overdoing it, i'd think something like this: simple 2.8L block, oversize valves and port/polish on the head. don't get too crazy with the cam, but get a sporty one for sure. strong ignition is crucial. i recommend electromotive xdi or the equivalent. i probably won't upgrade to ITBs for another 1-3 years. at that time i'll probably sell my carbs, all my jets (over 120 jets in total), literature, and extra parts, everything sold as a set ideally. PM me if anyone wants to know more. Edited April 26, 2010 by zredbaron Quote Link to comment Share on other sites More sharing options...
yetterben Posted April 26, 2010 Share Posted April 26, 2010 You really need a wideband man. All the money on jets and no feedback really. I cant stress enough i never had a flat spot ever. When i set mine up i dialed it in at high 11's that way Buy the time the transition came in it was about 12.3 for a split second before the mains cam online. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted April 26, 2010 Share Posted April 26, 2010 (edited) Mark, I totally agree with you, the "crazier" the project becomes, the harder it is to tune properly at low rpm. The setup you advices is actually exactly mine: Stock block (F54 redone), street port/polish P79 head by Braap, street Rebello cam, 40DCOE with 32mm choke, Mallory unilite + hyfire 6AL for ignition. I'm still in tuning mode, the engine is very nice to drive on the roads whereas AFR & timing tuning is not fully done yet (very rich, pinging a little at 3000rpm under load) So for the moment, I did not mess around with the air horn. Regarding ignition, mine is actually quite ok as far as power and tunability but I'm far away from being optimal. An electronic and fully customable system such as the XDI or Megajolt are on my wish list When I look at your picture, I can see that we have the same intake manifold, the same air horn length and Webers (not the same diameter though). I've observed on many old cars with Weber how the horn was. A lot of them have very long ones. Since I've changed many things in my setup, I will immediately see with the wideband if the spot is still present. So far I'm not so concerned by WOT, so this analysis will come later I'm not doing any log for the moment since I'm checking idle, cruising and low rpm (I'm messing around with idle jets, idle tuning, carbs sync & acc jets) Yetterben, I'm using a wideband to tune my car. I'm also going to use a detcan to timing optimization. If I'm not mistaken, Mark is also using a WB. I've got your point: it makes no sense to invest $$$$ into custom head, carbs , jets and not have a 300-400$ wideband system. It is because we have a wideband with datalog capabilities we are able to see this flat spot. I cannot really see it when driving the car and look at the wideband screen. Edited April 26, 2010 by Lazeum Quote Link to comment Share on other sites More sharing options...
zredbaron Posted April 26, 2010 Share Posted April 26, 2010 i absolutely agree that a wideband is essential. the narrow band is also a quite useable tool, but definitely more demanding. the [narrow-band] autometer gauge doesn't display a stoichiometric value, but rather an analog style LED throughout a range of lean, stoich., and rich. i have the car tuned to the point where at WOT above 4000 rpm (cam is at beginning of power band at this point) it reads on the leaner side of the stoich. range, just where the fuel manufacturer recommended. before 4000 rpm, i have to feather the throttle to achieve this display. it's not hard to learn what the engine wants. if i were to floor it at 2000 rpm, the car would fall flat and the display would go blank (in the rich direction). too much fuel, not enough airspeed through the venturis to atomize the huge drops of fuel into a fine mist. it doesn't fully fire, leaving the cylinder full of fuel until most of it clears out via the exhaust valve. but yes, i do desire a wideband. a blank display isn't very useful. autometer doesn't offer a wideband that matches my line of gauges, and i won't install one that doesn't match. oh, well. a wideband will simply show me how low my AFR goes, which really doesn't matter since i can't change it and will still have to avoid it via the pedal. it is easier to read, though. regarding the long air horn, that's the old style. aerodynamically, without an air box, it straightens the air out more than the shorter one, producing a more consistent airstream and ultimately a more even burn. i think you can still buy it, there just isn't quite room for it in our cars unless we don't put a filter on our carbs. not something i was ever willing to do. all the F1 cars had long horns. and smaller slugs. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted April 26, 2010 Share Posted April 26, 2010 also, matt, does your mallory distributor have a vacuum advance? if so, i'd say you have a pretty decent ignition setup and should be fine. Quote Link to comment Share on other sites More sharing options...
yetterben Posted April 26, 2010 Share Posted April 26, 2010 I would increase the idle jet really to surpass the stumble. I would also back out the mixture screws more to richen up the idle to compensate for the stumble. Quote Link to comment Share on other sites More sharing options...
zredbaron Posted April 26, 2010 Share Posted April 26, 2010 I would increase the idle jet really to surpass the stumble. I would also back out the mixture screws more to richen up the idle to compensate for the stumble. really, dude? have you read the thread you're posting to? by increasing idle jet size you're suggesting to add more fuel to an already over-rich condition, and then you also want to richen the idle mixture? Quote Link to comment Share on other sites More sharing options...
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