adam.

I will first need to see what my OER idle air bleed sizes are, whether they're equivalent to F8 or F9 etc and go smaller to richen up my circuit. I believe the #55 idle jet size itself is spot on.

So after a bit of reading, I think I may need to decrease the air bleed sizes on my idle jets. Since OER do not offer different sizes, I may need to start using weber idle jets. I am running lean at the upper end of my low speed circuit, which can be controlled by the idle jet's air bleed. And because I am running lean, I need smaller air bleeders.. Can someone confirm that this may/will work?

I honestly don't know. They dont appear to have any markings on it when I last had a look. They were the ones which came with the carbs new if that helps at all..

I had a feeling it may have been this dreaded transition but I wasn't sure of their effects. Now that you both have mentioned it though, when I got to 3krpms through activating the pump jets, I could WOT it from there without hesitation. So it must be the transition.. Damn. Increasing fuel levels made no difference unfortunately.

Okay, so I tried to get the car dynod yesterday and the car just broke down. The air temps were a tad cooler than the other day when I got the carbs to run spot on, but I think it's now running lean again... Idle is still around 13:1, cruise is not far off that, but slow/medium acceleration between 2-3krpms, it just loves to go up to and over 14:1 and stutter/miss/carry on. I can only get around it by accelerating and then while keeping an eye on the AFRs, jab the throttle to activate the pump jets to richen it back to 12-13:1 AFRs every few seconds which is quite annoying and isn't the way a car should be driven. I am really puzzled as to why it is doing this. I tried dialing out the idle/pilot mixture screws again like the other day but it had no effect whatsoever.

Thanks As pointed out by Blue earlier on in the thread, OER carbs recommend 2 turns out, plus or minus half a turn. Mines currently at 2.25 out which is within spec. And I'm glad. Time to get it on a dyno and see if the triples can crack a higher than 83rwkw it has with the SUs.

So I had a chance to tinker a little yesterday evening and following Blue's diagram of how the idle screw adjustments affect cruise and idle AFRs, I simply just dialed in a little more fuel (turning another half turn on the idle mixtures) and the lean hesitation on cruise and acceleration has disappeared (for the most part)! Here's a graph of me taking off in first gear, shifting until forth and then cruising and then slowing down to idle. As you can see, the rich dip after the gear changes are still there, but the pump adjustment is at the point where there is no longer lean pops after aggressive WOT at low RPMs. So as long as that works, I am not too fussed about the rich dip on gear changes. Second gear acceleration goes a tad lean as you can see but there's no hesitation and with the light load, I am not too fussed once again. Third gear onwards is fine. Cruise is at about 13.5:1 which I am happy with and idle is around 12-13 which is on the rich side but if everything else drives fine, I am happy with that! I believe under WOT, the mid range is in the 12.5-13 AFR range but top end is a little rich meaning I need larger air correctors which I don't have. Other than that, I am quite happy with how the car drives now. Feels amazing. Thought I'd update you all! And thanks again for the tips and help.

http://lupinusflower.ocnk.net/product/58 This is the fuel level gauge I use, Reverend. It's a fairly basic tool which I believe you could make one up yourself..

Being the first set of triples I have ever played with, I'm not 100% sure, but I would say I think they're right! Linkages themselves are the same length and are adjusted so that the open at the same time. I only have an old school unisyn flow measuring tool. At idle, it is quite hard to measure because there's so little vacuum but I can gauge the level of flow enough with it. I will have another little play around and try to remove that accelerator pump factor and report back soon!

Once again, awesome feedback Blue. Much appreciated. Removing the pump jets is one thing I really need to do to eliminate the possibility of it richening my mixtures, I will have to source a bolt that fits. And going from 31-29mm float levels, I kept all mixture screws and settings the same. It is honestly quite hard to tell idle AFRs though, bounces around quite a bit. I have been getting average figures for them. I will give it another go without the mains installed and remove the pump jets. Worse case, holding the car at 1, 2, and 3krpms. Thanks!

The carbs are brand new, yes, and I have adjusted the float and jettings from standard. Standard venturis were 36mm and I have reduced them to 34mm with 'ideal' jets to suit. I can't raise the fuel float level any higher I'm afraid. The middle carb's float adjusting screw bottoms out at the current setting which is showing 29mm on the glass measuring level I have. I don't think I should force it either. That's an awesome graph you have there though, I will have to play around with the mixture screws and see if it makes a difference to the driveability, even if it means sacrificing idle AFR mixtures. Unfortunately there is no port on the new manifold or carb to get a vacuum reading for the distributor advance. I have thought about the timing being off, but I have not heard any visible knocking yet which I guess is always a good sign.. I will tone it down a little bit if the above tips from Blue fail and see what it does. Please keep any other ideas you may have coming! Would increasing fuel pressure help with the lean? Is it a good idea to use fuel pressure to tune?

Ok I have had a chance to play around with it again today. Once again, just the idle jets were installed, I first trialed it with all mixture screws fixed at 2 turns out from full lean. This is at 31mm float levels, #57.5 idles. Graph is from take off in first until 3krpms and then shifting into 2nd, and again driving it until 3krpms with light acceleration. As if you would accelerate to a 35mph (60kmh) speed limit. As you can see, it slowly gets lean as it approaches 2.5krpms until 3kpms at gear change. Idle AFRs sat at around 12:1, cruise it is at ~12-12.5:1. I then adjusted float levels to 29mm. Everything else remained the same. Once again, take off from stand still in first until 3kprms where a gear change into 2nd is made, and then again until 3kprms at light acceleration, as you would to 35mph. As you can see, there's a slight improvement up and around the 2.5krpms range but it still leans out a little too much causing coughs and spluttering. Cruise is still very similar at around 12-12.5:1 AFR. I then thought I would install the #135 mains with #190 airs. Unfortunately don't have a graph for this, but slow acceleration felt like it improved a little bit more again. Hesitation reduced but was still there and annoying. WOT was good from above 3krpms, AFRs in the 12.5-13 range until top end where it richened up to about 12.2:1. Idle and cruise mixtured stayed the same. And then I kept the above setup and installed #55 idles to see how it would drive. Same procedure as before, slow take off in first until 3krpms, shift into second until 3krpms. Ignore the second half of the graph. On take off, AFRs are around 13 before 2.2krpms where it leans out and stumbles. Cruise is now around 14:1 which is nice but it is jerky and pops quite frequently at ~35mph (60kmh). At higher speeds it is quite comfortable. Idle AFRs are floating around 13:1. And that is currently where I am at the moment. I have noticed that the stumble is not noticeable when I accelerate a little harder, as if I was going to 80kmh but any lighter and there's hesitation. I cannot raise the float level any higher than it is at the moment (29mm). Any help would be much appreciated!

Update: I have received #55 and #57.5 idle jets, the #55s are still too lean to even accelerate, while the #57.5s have a cruise AFR of 12.5 and acceleration is in the 13s - 14/15 which cause stuttering (around 2.3-3krpms). Idle is about 13. Any ideas what could cause this lean spot causing the stutter? I cannot get my head around it. I have tried checking timing and best I can do is 15 degrees at idle. It seems like I can't get cruise any leaner without causing hesitation on acceleration. The #57.5 are 1.5 full 360 degree turns out from full lean. Really struggling.. I think it's that dreaded transition lean.

Wow, thank you so much, Blue. I have read quite a few topics in the past and your posts have been very helpful in me understanding how.. Zs work! Not just carbs.. With the information you have just posted, together with what I already know, there shouldn't be anything else stopping me from getting these tuned. You've basically cleared up any doubt I had regarding mixture screw adjustments ( I thought 3/4-1 full turn was the aim) and tuning of the mains. I will have a read of those links in your last post over time. Cheers

I have only really ever tuned the SUs in the past. These are the first set of triple carbs I have ever played with, so you can say my knowledge is fairly limited although I feel like I have done quite a bit of research into them, understanding how they worked, etc. How I've come to my jets has been through research and following 'rough' jets of other similarly modified Zs/L28s. The OERs originally came with 36mm venturis and I followed the venturi size multiplied by X plus X for air corrector formula. Idle jets were the only thing I guessed (following what others ran). From there, I tried it for myself, used my wide-band and ended up with the above jets which is currently running in the car. And as for mods, I completely forgot to mention that I am running an electronic distributor from a 280zx. Other than that, the motor is standard. I have only replaced the head due to corrosion. Standard cams. Cheers Edit: I should probably also mention that I have performed a leak down test on the motor and all is well with leak figures measuring no more than about 18%. So the motor is still fairly 'fresh'..

With the #60s installed and producing AFRs of ~11 at cruise, I just thought #50s would still run, albeit a tad lean. Looks like I will have to get my hands on a set of #55s.

Hello all from Australia, Long time browser, first time poster here because I finally can't find the information I'm looking for! First off, my name's Adam and I have a 1973 240z which is currently running a standard L28, N42 head/block combo, with brand new triple 45mm OER carburetors, and Trust headers to a twin 2" exhaust system. I have just installed a new set of OER carbs I purchased from Japan and am having difficulties sorting out the idle/low speed cruise setting. Bit of details into the setup, 45mm carbs 34mm venturis #190 air correctors (not yet tested to see if these are the best) #130 mains #60 idles #40 pump nozzle #1.8 needle valve 3.5psi fuel pressure from the mechanical fuel pump into Holley regulator 31mm fuel level using the OER level gauge. Idle screws are setup so that the first progression hole is just 100% covered looking through the brass cap/inspection hole. Carbs are balanced the best I can using a unisyn. I have a wide-band O2 sensor probe in the tail pipe. I am running 98 octane fuel. Timing is at 15 BTDC with no vacuum advance connected. Valve clearances have recently been adjusted. Now, onto the problem I am having.. Driving with the #60 idles installed, 1 full turn of the mixture screw turned out, slow acceleration and cruise is very rich, 10.5 and 11.5 AFRs respectively. I also have #50 idles on hand which I have installed to try and improve the current rich scenario and I cannot even get them to idle. With mixture screws out 1.5 full turns (recommended range is only 3/4 to 1 full turn), they cannot idle on their own, only when I blimp the throttle which I believe is activating the pump jets. With the #50s installed, AFRs are off the scale in the lean area. They can't idle let alone drive. My question is, is going down from a #60 to a #50 idle jet that big of a jump that the car can no longer idle on its own? Or is there something wrong with my idle screw setup? OER offer a #55, but I would like to double check with the experts out there first before spending that money. Any help would be appreciated. And please let me know if I am missing some information, I tried to be as detailed as possible. Thanks, Adam