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Thread: holley 4 barrel question

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    Default holley 4 barrel question

    Hi, I'm a new Z owner. The car came with a Bob sharp and Holley 8007 390 cfm 4 barrel conversion. The carb secondary vacuum barrels were seized probably since he garage it 12 years ago. I tried a rebuilt kit but still had problems and I didn't trust it as a daily driver. So being new to carbs I asked around and was advice to just replace them. I purchase a new Holley 600 cfm 4 barrel carb thinking that more cfm is better. Now the car turns on with minimum effort and idles ok. Once the motor warms up I open the choke and it starts to idle high and goes up and down in idle from 800 to 1200 and seems as though its running rich. Ive revived all the way just to see where recline is and it on occasion has passed 8000 rpm. Air/fuel has been adjusted with vacuum faucet but its a self float adjusting carb. Not much to adjust except jets. My question is : is the larger 600 cfm carb to blame for all problems or can it be something else. I figured bigger carbs =higher idle and more gas consumption but not sure about rest. Thank for any help you can give. Sorry for the long post but I figure all the info I can give couldn't hurt.

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    Did I post in the right section?

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    Not a 100% sure but I believe my buddy in Vegas runs the arizona holley carb setup and he said you can only run with a 390 cfm max. Stock 260 engine. You didn't say what Z you own either. You need to supply more info about the engine also....stock, 240, 260, 280, etc, etc. You may want to check arizonazcar.com also.

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    Sorry, miss that. Its a stock 240z rebuild motor. But I cant confirm unless I take it apart. I feared the bigger carb is the problem, Ill confirm with arizonazcar.com thanks.

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    Registered User Walter Moore's Avatar
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    Yes, too big of a carb is always a problem. If you don't flow enough air through them the mixture will never be right.
    '71 240Z, Because any fool can drive fast in a straight line.

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    you need to run a 390 cfm max as was said in an earlier post.
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    Thanks everyone, i will try and get old 390 cfm carb to work or just buy a new one. Would the larger carb explain the motor revving pass 8000 rpm. I cant really imagine the motor being able to handle it without any modifications or is there no rev limiter on the l24?

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    No that's not a carb problem....maybe linkage? Get the 390 on it and see how it does.

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    Quote Originally Posted by azkyinc View Post
    Thanks everyone, i will try and get old 390 cfm carb to work or just buy a new one. Would the larger carb explain the motor revving pass 8000 rpm. I cant really imagine the motor being able to handle it without any modifications or is there no rev limiter on the l24?
    Correct, no rev limiter on stock ignition.

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    Quote Originally Posted by azkyinc View Post
    The car came with a Bob sharp and Holley 8007 390 cfm 4 barrel conversion.
    Well there's your problem! Down-draft carbs don't belong on an inline engine, especially one with high-performance in mind. Some will be drawn to contradict me because their's runs great, but that setup is just inherently inferior to proper side-drafts.

    Slap on some SUs (or triples) and be done with it. People make the 390cfm "work" but that 600cfm Holley is probably no where near jetted correctly for your engine.

    Oh, and there is a rev limiter on the L24, it'll stop revving once you see a piston flying through your hood!

    An SU-equipped L24 will rev to 8000rpm just fine, just ask Greg Ira.
    Last edited by LeonV; 03-16-2012 at 09:15 AM.
    2/74 260Z

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    Quote Originally Posted by LeonV View Post
    Well there's your problem! Down-draft carbs don't belong on an inline engine, especially one with high-performance in mind. Some will be drawn to contradict me because their's runs great, but that setup is just inherently inferior to proper side-drafts.

    Slap on some SUs (or triples) and be done with it. People make the 390cfm "work" but that 600cfm Holley is probably no where near jetted correctly for your engine.

    Oh, and there is a rev limiter on the L24, it'll stop revving once you see a piston flying through your hood!

    An SU-equipped L24 will rev to 8000rpm just fine, just ask Greg Ira.
    Agreed, you're cheapest, fastest and best end result is to go with a set of stock SU round top carbs. Have never heard anyone say they have a reliable 4BBL driver.

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    Quote Originally Posted by 5thhorsemann View Post
    Agreed, you're cheapest, fastest and best end result is to go with a set of stock SU round top carbs. Have never heard anyone say they have a reliable 4BBL driver.
    Boys, please help the guy out here...some people like to do things a bit differently and that should be respected, not dissed. AND my 4 barrel Holley setup runs beautifully,. Took some work but the fruits are there for my effort. Magic doesn't happen without waving ones wand.

    There is a small but loyal following of people running 4 barrel carbs on their sixes. Not all of them run Holley's but most do. I do. The most significant thing about running a 4 barrel is the manifold that it's bolted to, not necessarily the size of the carb you use. The effect of the manifold is dramatic in the way the carb has to be tuned. The V8/carb boys understand this the best, they know an 850 double pumper wont work well at all on a high rise single plane manifold on a 4V headed Boss 302 Cleveland motor for the street, for example. However, with the same carb, a dual plane torquer manifold will be far more civilized than the other manifold. The jetting and power valve values will need some adjusting too because of the reversion effect and harmonic tuning that takes place when you begin to separate the firing into two groups, like you do when you apply a dual plane manifold to an engine. Detailed theory is out there if you want to dive into it that much. What the HELL has all this to do with our engine, an inline 6 cylinder? Lots.

    The manifolds that can use a four barrel carb are out there. Did you know that NISSAN made a 4 barrel manifold for the L series six? They did. I have one. It was an evolutionary thing from the down draught 2 barrel carb that nissan designed for their domestic and some export market cars that had sixes in them. The 4 barrel verion was fitted to a domestic market car only. Arizona, Clifford and Cartech all make manifolds/adaptors for 4 barrel conversion. Depending on what you use will determine what type of 'induction' you'll be left with. The Arizona will be a true 'dual plane' setup, the Clifford a single plane (can be modified into a dual plane) and the Cartech will adapt the twin su manifold to a single plane type manifold. A dual plane manifold will never have the top end of a single plane or that of triple carbs but a Clifford single plane can match a dual su carbed engine setup for top end power.

    A 600 cfm carb will work on all of these manifolds. I know, I've used one. The top end was great and I achieved over 103 rwkw in a stock N42/N42 combo through an auto trans (L3N71B) with the air and steer belts on and the fan in place. Why don't I run this on my car now? The response down low was average, economy average and if get really picky, thought that I could do better. Power at the top end isn't everything for a daily. For the track.....fantastic....but not the street. The process continued, testing this one, combining it with that one and ended up with a 465 Holley on a Arizona dual plane manifold. My old Cedric weighs in at almost 1500kgs. For a responsive drive, I chose this combo. It's fantastic...reliable, economic, torquey and 'different'.

    In summary, you can use a 600 and on an Arizona manifold, it's not bad, you'll just need to work it to get it to work as you'd like it to. No free lunch unfortunately.

    Good luck with it mate. Cheers.
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    E32 manifold and with throttle body injection for something 'different' Lol.
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    Mark, thanks for that. I'd much rather hear an answer from someone based on their own expierence rather than the anecdotal stuff you always seem to get when someone asks such a question.
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    I thank all of you for your input specially ozconnection for the all the information, its steering me in the right direction. I'm definitely going to do lots more homework on 4bbl to get the tuning just right. I really want to stick with the 4 bbl carburetor since I'm already knee deep in the project . By the way ozconnection, who makes the E32 manifold and with throttle body injection? Thanks again guys.

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    Quote Originally Posted by sblake01 View Post
    Mark, thanks for that. I'd much rather hear an answer from someone based on their own expierence rather than the anecdotal stuff you always seem to get when someone asks such a question.
    I would hope that you're not referring to my post as "anecdotal", unless you don't understand the reason why down-drafts are at an inherent disadvantage to side-drafts.

    Like I said, people make it "work". Mark is a good example of that (and knew he'd chime in ) and am not saying that his setup is "bad". I don't deny that max power numbers can approach stock SUs, but as Mark found out, this involves greater compromises in other areas.

    Here's a quick rundown:

    (1) When mounted on an inline engine, the air coming in through a down-draft carb must make a 90 degree turn in order to line up with the intake runners. This leads to a pressure drop (loss).

    (2) The fuel must make the 90 degree turn with the air. This leads to more fuel pooling underneath the carb. This makes tuning more difficult and inefficiencies in transient conditions.

    (3) The manifold geometry is forced to make the central runners shorter and the outer runners longer. This leads to a more uneven air-fuel mixture distribution and forces you to run a richer mixture in order to get enough fuel to the lean cylinders, while you dump more fuel in the cylinders that already had a good mixture.

    (4) Because of the manifold geometry, pairs of cylinders are tuned to differing rpm. The middle cylinders breathe better at high rpm, while outer cylinders breathe better at low rpm. This doesn't allow for intake tuning to be as effective.

    This is an explanation of the main disadvantages. It is not to say that those that use 4-barrel carbs are wrong, or that they should change. Everyone is free to do as they wish. If someone thinks that a 4-barrel is the bee's-knees, then so be it! I find it is good to provide information and let the end-user make their own informed decision.

    Good luck with your 4-barrel, azkyinc.
    2/74 260Z

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    Quote Originally Posted by LeonV View Post
    I would hope that you're not referring to my post as "anecdotal", unless you don't understand the reason why down-drafts are at an inherent disadvantage to side-drafts.
    No, I just meant in general.
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    Quote Originally Posted by azkyinc View Post
    I thank all of you for your input specially ozconnection for the all the information, its steering me in the right direction. I'm definitely going to do lots more homework on 4bbl to get the tuning just right. I really want to stick with the 4 bbl carburetor since I'm already knee deep in the project . By the way ozconnection, who makes the E32 manifold and with throttle body injection? Thanks again guys.
    Genuine Nissan E32 intake manifold. You can't just go and buy one of those E32 manifolds, it took me quite a few years to find one AND at the right price. That injection throttle body (with megasquirt) is for a future project I have in mind for my coupe. You can buy those on ebay. Cheers.
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    '71 240C coupe N42 NEW E88 FS5W71B 4.33 H190 Megasquirt V3.57 212 rwhp

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    azkyinc, post how you make out with the 4 barrel setup. I'm curious. It's nice to have people to run your ideas by. People that are willing to post ideas and info regarding your situation. I'd rather hear something that might be able to help me, give me something to think about, than to receive no help at all. All too many times I see people post nothing regarding the members question(s) like one post above. Keep us posted on your progress. My buddy in Vegas is trying to talk me into the arizonazcar setup. It is what he is running and is happy with it. I'm not convinced it's the right thing to do yet.

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    xxxxxxxx
    Last edited by sblake01; 03-17-2012 at 07:21 PM. Reason: pointless comment.....
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    hehehe

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    Thanks you all the information it has really help. everyone here has given both sides of the picture which has let me know of my options.

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    Update: I'm waiting on a jet kit to tune it right. Still cant get it to idle right ( might be putting up a video on the problem, if i could figure out how As for now finishing up the body work and getting it ready for primmer and paint. I was also suggested that upgrading the ignition system and switch to and electric fuel pump might help with the 600cfm setup so please let me know if that would help.

    rcb280z: I'm not sure if the bob sharp and the arizonacar setup are the same, but from what i have read the only difference is the throttle linkage is different. once i get it all working right i will have it dyno and post the numbers up so you can get a good idea of what its capable before you decided. Thanks again.

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    A quick reply....an electric fuel pump can be a good thing...you can check the float levels without the engine running, for example. An ignition upgrade is simple and effective for ignition reliability and consistancy.

    The jet kit you mention, what parts does it have? Jets won't effect the idle. Get the idle right. You may need to go to your library and borrow a Holley book or two and read up on the subject if you don't have much experience. If you have time...then take it...don't rush. Understand what you're doing. Throwing parts at a carb doesn't mean success.
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    Your right , this is all new to me. Is there any particular books you recommend? I did try putting in the jets from the old 390 cfm carb on the 600. Alot of the white smoke from the tail pipe is gone except on hard acceleration ( 600 cfm jet size 65 and 390 cfm jet size 45). One thing i did notice is the car went through 4 gallons of fuel just revving and idling in the garage for warm up ( hasn't been driven) Is that common? thanks

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    Quote Originally Posted by azkyinc View Post
    Your right , this is all new to me. Is there any particular books you recommend? I did try putting in the jets from the old 390 cfm carb on the 600. Alot of the white smoke from the tail pipe is gone except on hard acceleration ( 600 cfm jet size 65 and 390 cfm jet size 45). One thing i did notice is the car went through 4 gallons of fuel just revving and idling in the garage for warm up ( hasn't been driven) Is that common? thanks
    The Holley book by Dave Emanuel is the first Holley book I ever bought. It is a good starting point. There are others out there and i have a great collection. They provide different perspectives or solutions and that is what I'm often looking for in a new book.

    Changing jets from the 390 into the 600 shows that you're willing to "get stuck into it' but again I say with respect, you gotta know what your doing man. You cannot simply change the jets over like this. The effect is so dramatic by 20 jet sizes, you'll never get the engine to run right, it'll be so lean it'll pop and fart like a bastard and you run the very real risk of burning the valves out or putting a hole in your piston. I cannot stress this point enough. Understand what you're doing by doing some reading up first. Put those 600 jets back in.

    Test running the engine in your shed isn't really tuning.....the only real way is to take it for a drive and drive normally. Not flat out but normally. Come to a stop and see how it idles. Drive it slowly and does it snatch/jerk? A slight uphill gradient, does it pull smoothly or does it have a flat spot where adding throttle doesn't result in more power? How do the spark plug electrodes look after the spin...black or tan? Things like that. For me, to get the car where I wanted it took some weeks of weekend driving. Each trip was for 20-30 minutes. A 2 minute blast around the block barely gets it warm so you'll never really get to see whats wrong or right with your carb. calibration.

    Change one thing at a time. Then try it. Write this in big letters across your forehead if you have to. These few words will be the best advice anyone will ever give you. Don't forget them or it will take longer than a few weeks to tune your carb.

    Take detailed notes. Make notes of how the car went/felt after the 20 minute drive. Leave yourself impressions. Score things out of 10 for example. Idle hot 7/10 idle cold 9/10 slow running 7/10 sudden accel 9/10 etc. From this you might conlude several things....don't tweek the idle screws, the auto choke setting, the power valve all at the same time, do one thing and then rescore. You might find things improve where you thought things wouldn't and at this point you'll begin to understand the interrelationships between the different circuits inside the carb and how these circuits "overlap' each other.

    Get that book and start learning. You wouldn't sit an exam without some study first would you?. Give yourself the opportunity to succeed man.

    Cheers!
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    quick update: still waiting on the jet kit. went to the library but they didn't have any Holley books available. If someone know any title that are helpful please let me know. Perhaps a can download them on my e-reader. Im also moving to Florida in a month, would that mean i would have to tune the carb again because the change in sea level? thanks again all.

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    update; still waiting on the jet kit. i think i found the reason for the fuel disappearing , i found a broken fuel hose that comes out of the tank. since i am able to drive it now more problems have. now it bogs when accelerating unless the choke is half way close. i have read its because the pump shot is too small or the secondaries aren't opening in time. also not related to the carb but the passenger rear wheel is lower than the rest. is that something common in Z ? thank again everyone.

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    update: After fighting with the larger carburetor, i have returned to the smaller 390 cfm. every times i got one problem fix another would pop up. when i changed the jet it fixed the rich condition but create a problem were the secondaries are creating too much vacuum and its constantly sucking in fuel bring back the rich problem. Also i could never get it to idle right, guess I'm just going to keep the 600 cfm carb for a future boosting upgrade where the larger cfm is going to be combined with a supercharger. Thanks all for all the great advice, it came in handy. At least i learn a lot from this.

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    I spent the early part of my life tinkering with Holley carbs. They are wonderfully easy to mess with, and simple to work on. The have very understandable primary and secondary circuits.

    but OZ connection is right. The key to a good running engine is knowledge first and foremost. Read as much as you can on holley vacuum secondary carbs, then gain as much data as you can.

    Forget about the library, go to amazon and BUY that holley book. It will serve you well. You will gain something new each time you read it.

    Also I will echo, you cannot tune a car with carbs sitting in neutral. It does not work that way. The engine needs load to produce driving conditions.
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    Some of you guys will probably flame about this but the colortune tool helps out quite a bit when your a novice at carb tuning. At the very least tuning at idle will give you a decent starting point which at the moment azkyinc is nowhere near, then follow the guidelines ozconnection suggests for actual tuning. Here's a video demonstrating colortune: http://www.youtube.com/watch?v=xEZ0-uN0NA4
    Its also my opinion that carbs almost never need to be replaced. A full rebuild will replace basically everything that isnt metal so unless the carb is rusted out it can be saved. Carb tuning is a lost art i was only able to pick up because of motorcycles and even local old timers haven't dealt with it in so long they have lost their touch.
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    Quote Originally Posted by Kurbycar32 View Post
    Some of you guys will probably flame about this but the colortune tool helps out quite a bit when your a novice at carb tuning. At the very least tuning at idle will give you a decent starting point which at the moment azkyinc is nowhere near, then follow the guidelines ozconnection suggests for actual tuning. Here's a video demonstrating colortune: http://www.youtube.com/watch?v=xEZ0-uN0NA4
    Its also my opinion that carbs almost never need to be replaced. A full rebuild will replace basically everything that isnt metal so unless the carb is rusted out it can be saved. Carb tuning is a lost art i was only able to pick up because of motorcycles and even local old timers haven't dealt with it in so long they have lost their touch.
    The Colortune is an antiquated tool, made obsolete by affordable wideband O2 systems. A Colortune may help in getting your idle mixture close, but that's about all you can accomplish with it. I can accomplish essentially the same result, just using my ears.

    Save your money and get a WBO2, you'll never look back. Knowing what your mixture is at any rpm and any load is enormously helpful information to have. It doesn't matter whether you're a novice or a pro, it's flat out a far more useful tool.
    2/74 260Z

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    Flame on! Seriously though I would appreciate a link to an affordable, portable WBO2 tool. All of the ones I have seen are over $300. I don't dispute its value but remember us younger guys haven't had to tune a carb by ear, carbs were basically non-existant on cars a decade before i started driving. The colortune wont give you a complete tune but for 60 bucks you can throw it in your toolbox and use it on your motorcycles without welding o2 bungs into every vehicle you use
    Early 1974 260z
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    Quote Originally Posted by Kurbycar32 View Post
    Flame on! Seriously though I would appreciate a link to an affordable, portable WBO2 tool. All of the ones I have seen are over $300. I don't dispute its value but remember us younger guys haven't had to tune a carb by ear, carbs were basically non-existant on cars a decade before i started driving. The colortune wont give you a complete tune but for 60 bucks you can throw it in your toolbox and use it on your motorcycles without welding o2 bungs into every vehicle you use
    We've had this discussion recently. There is no "flaming", just a logically presented argument. There is no need to take it personally.

    My WBO2 (14point7 Pure Plus) cost around $200 when I bought it 2 years ago, and the DIY version is under $200. They're probably a bit more expensive now, but there are others in that price range as well. Saving for a WB is easily justifiable when you consider the gains to be made from it. You can buy an exhaust adapter as well if you want to move it to your motorcycle, no bung needed. With that said, bungs aren't much of an expense anyway, plug them with a threaded plug when not in use and you're done.

    BTW, there is no age requirement to understanding and being able to tune carbs. Okay, you do have to be old enough to be able to turn a screwdriver and comprehend what you're doing. I'm probably not that much older than you.

    Saying that the colortune won't give you a complete tune is an understatement. It isn't really giving you any tune at all, just getting your idle mixture "close". I don't know about you, but my engine spends a lot more time under load than idling. That's a waste of $60, IMO. Like I've said, it's a novelty and if you think it's cool, by all means have at it. I think it's pretty cool to be able to essentially look into your combustion chamber. However, these days there is no good reason to recommended it for any serious tuning purposes.
    2/74 260Z

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    Its cool, im not taking anything personally. My main complaint against the WBO2 is that it basically requires installation on every vehicle. Yea the bungs are cheap but you need to cut a hole and weld it into any exhaust system you plan on testing which is not practical for tuning your buddy's carbs. They dont work on v-twin bikes and on 4 cyl street bikes unless you have one bung per exhaust port its a guess and check game to see which carb actually needs adjusting. I actually can tune a carb by ear but that skill comes with experience which the OP admittedly has none because carbs haven't been commonplace for decades. I dont dispute that colortune is obsolete and no its not a serious tuning tool. Colortune's main advantages are that its totally portable for use on basically anything that uses a spark plug, its inexpensive and will give you a decent starting point all while being totally usable by novice mechanics. I appreciate the 14Point7 lead though, I haven't seen that setup yet http://14point7.com and have been looking for something i could use for serious tuning

    \threadjack
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    Quote Originally Posted by Kurbycar32 View Post
    Its cool, im not taking anything personally. My main complaint against the WBO2 is that it basically requires installation on every vehicle. Yea the bungs are cheap but you need to cut a hole and weld it into any exhaust system you plan on testing which is not practical for tuning your buddy's carbs. They dont work on v-twin bikes and on 4 cyl street bikes unless you have one bung per exhaust port its a guess and check game to see which carb actually needs adjusting. I actually can tune a carb by ear but that skill comes with experience which the OP admittedly has none because carbs haven't been commonplace for decades. I dont dispute that colortune is obsolete and no its not a serious tuning tool. Colortune's main advantages are that its totally portable for use on basically anything that uses a spark plug, its inexpensive and will give you a decent starting point all while being totally usable by novice mechanics. I appreciate the 14Point7 lead though, I haven't seen that setup yet http://14point7.com and have been looking for something i could use for serious tuning

    \threadjack
    A WBO2 will work on any engine, whether it's a V-Twin or a V12. Tune one cylinder and mimic the jetting on the second one (or third, or 4th), it's not difficult. Like I said, you don't need a bung at all, there are clamps available that shove the O2 sensor down the exhaust pipe. Then, all you need are power and ground connections, also not difficult.
    Last edited by LeonV; 04-12-2012 at 03:56 PM. Reason: Clarity
    2/74 260Z

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    azkyinc, I too am a rather new Z owner and also acquired my Z with a Bob Sharp/Holley 390 setup. It actually runs very well and according to my butt dyno isn't too big of a slouch. The biggest complaint I have is that upon initial startup it will idle around 1000 to 1500 rpm....and then it bogs (it just dies). I start it up again and it idles for about 10 to 15 seconds and bogs once more. The whole process is repeated until I can sustain a steady idle, at which it will settle around 500 rpm. Typically, if i rev it past 4000 rpm as soon as I get it to turn over it will settle into that steady low idle much sooner. Other than that, my setup seems very reliable and I use it as my current daily driver.

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    http://www.youtube.com/watch?v=UPGLU...eature=related
    YouTube is the source of ALL knowledge.

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    Quote Originally Posted by JuanJaime View Post
    azkyinc, I too am a rather new Z owner and also acquired my Z with a Bob Sharp/Holley 390 setup. It actually runs very well and according to my butt dyno isn't too big of a slouch. The biggest complaint I have is that upon initial startup it will idle around 1000 to 1500 rpm....and then it bogs (it just dies). I start it up again and it idles for about 10 to 15 seconds and bogs once more. The whole process is repeated until I can sustain a steady idle, at which it will settle around 500 rpm. Typically, if i rev it past 4000 rpm as soon as I get it to turn over it will settle into that steady low idle much sooner. Other than that, my setup seems very reliable and I use it as my current daily driver.
    Assuming you have an automatic choke:

    The fast idle when cold is normal, to a point. The choke system has a fast-idle cam that increase the idle speed when the choke is on. The stalling right after start-up sounds like the choke pull-off is opening the choke too far. Both are adjustable. Follow the Holley adjustment procedure and it should be fine.

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    Hi all. Figured I'd post up in this thread.

    I have a '78 280. Removed all the FI. Installed Arizona manifold with Holley 390 4bbl, MSA headers, 2.25" exhaust, and MSD ignition. Then the car sat for about 5 years. Brought back to life last summer. Ran like crap (go figure). Couple weeks ago I pulled the carb and tore it apart. Ran it through my ultrasonic cleaner (several times) and rebuilt using Holley rebuild kit. Stock jetting was 51 mains. I downsized to 49s during the rebuild. Had a terrible time with lag when stepping on the gas. So I changed out the accelerator pump cam the other day. Original was orange. I changed to a cam with lower total volume and more linear delivery. Lowest volume I had was a black cam. That made a huge difference on acceleration. As in it actually does now without bogging down and hesitating. Still a lot of tuning to do. But at least the thing is back on the road and comfortably derivable.

    Now all I need to do is fix the stereo...
    ...And maybe do something obout the squealing front brakes.

    Later

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    well if you want to get really crazy, do not just tune the accelerator pump cam. Change out the squirter on top of the housing that discharges fuel into the carb. Those made a huge difference in the way the fuel is delivered. You can really tune a holley to do darn near anything once you get an understanding of the circuits.
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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    600 cfm waaay too big even for a 2800 cc motor. It will NEVER run right.

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    Quote Originally Posted by Zedyone_kenobi View Post
    well if you want to get really crazy, do not just tune the accelerator pump cam. Change out the squirter on top of the housing that discharges fuel into the carb. Those made a huge difference in the way the fuel is delivered. You can really tune a holley to do darn near anything once you get an understanding of the circuits.
    What size squirter did you go with? And have changed the diaphragm spring on the secondaries? If you did, harder or softer? And finally, what size main jets are you running?

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    OH man, Okay, lets be clear. I use to run Holleys on all my Drag Cars I use to play with. I started with typical vacuum secondaries then moved on to double pumpers. Which was easy since it is the same with two sets of primaries. But I have long since forgotten about which one I used. I had about a half dozen in my carb tuning kit, about a dozen jets, and about a dozen cams. I also always had a power valve or two just sitting in there in case.

    I NEVER changed the diaphragm spring on the secondaries. I do not think you need to unless you are just dying for fuel. Here is a rule I remember reading about. IF you can feel your secondaries kick in, the tune is off. They will only really open at high load settings anyway in the upper RPM band. The engine will only pull what it needs from the secondaries. So it is sort of self tuning to a degree. That is the beauty of the vacuum secondary carb. It is a great design.

    You are at that point were you are trying to make very fine tuning adjustments. If the car starts and idles and runs without any noticeable flat spots then you are over half way there. I spent months thinking with my Holleys trying to eek out a tenth here and there, but I had a measurable metric. I had a 1/4 mile time. And I could tune for a specific thing, which was drag racing. Coming out the hole hard and then staying in the sweet spot to red line under Wide Open Throttle.

    From what I gather you are not doing drag racing runs which can be used to quantify your results. So you can get into the circle of chasing a fantasy perfect setting where the whole car will wake up instantly. The truth is that probably will not happen. If you have a lean spot or an off idle stumble then yes, that can be tuned away to a degree. But if the car is running decently with your Holley, then without a yardstick to measure your results, you may end making things worse more than you make them better.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Hell, I'm happy I just got the thing running again. I probably won't mess with it too much. I'd really like to (and plan to) go with triple webbers. But they are so damned expensive and the wife says I'm wasting enough money on my two wheeled "projects" at the moment. My biggest concern is going to be passing the DEQ test (emissions test) that is required in the Portland, OR area. Never had to try passing that before.

    Drag racing a "Z"? That sounds like fun...

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    I saw in your previous post that you've put a new exhaust system on. They will look under the car with a mirror for a catalytic converter if the door tag says it's supposed to have one. Just a heads-up for you.

    As far as the idle emissions spec. you'll get multiple tries to get it right. No fees until you pass.

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    Catalytic converter... OMG. How am I supposed to have any fun with my "project" if they are going to make me conform to the will of "Da Man"? I'll have to check tomorrow and see what stickers are still on the car. Maybe I can pull out the middle glass pack and put in a cat. Still have flowmaster at the end. Once DEQ is done, put the glass pack back in. Registration is good till December. So I have a bit of time to sort the car out. Hell still have tuning to do on the carb for heaven sake.

    Washington county Zed? I'm there as well. Hillsboro.

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    Smile

    Quote Originally Posted by Zedyone_kenobi View Post
    OH man, Okay, lets be clear. I use to run Holleys on all my Drag Cars I use to play with. I started with typical vacuum secondaries then moved on to double pumpers. Which was easy since it is the same with two sets of primaries. But I have long since forgotten about which one I used. I had about a half dozen in my carb tuning kit, about a dozen jets, and about a dozen cams. I also always had a power valve or two just sitting in there in case.

    I NEVER changed the diaphragm spring on the secondaries. I do not think you need to unless you are just dying for fuel. Here is a rule I remember reading about. IF you can feel your secondaries kick in, the tune is off. They will only really open at high load settings anyway in the upper RPM band. The engine will only pull what it needs from the secondaries. So it is sort of self tuning to a degree. That is the beauty of the vacuum secondary carb. It is a great design.

    You are at that point were you are trying to make very fine tuning adjustments. If the car starts and idles and runs without any noticeable flat spots then you are over half way there. I spent months thinking with my Holleys trying to eek out a tenth here and there, but I had a measurable metric. I had a 1/4 mile time. And I could tune for a specific thing, which was drag racing. Coming out the hole hard and then staying in the sweet spot to red line under Wide Open Throttle.

    From what I gather you are not doing drag racing runs which can be used to quantify your results. So you can get into the circle of chasing a fantasy perfect setting where the whole car will wake up instantly. The truth is that probably will not happen. If you have a lean spot or an off idle stumble then yes, that can be tuned away to a degree. But if the car is running decently with your Holley, then without a yardstick to measure your results, you may end making things worse more than you make them better.
    That's some solid info right there!

    As far as the accel pump setup is concerned, it's way too big for our little sixes. The volume of fuel that can be delivered by the accel pump can easily flood our engine. The carbs were originally designed for a much larger capacity engine, so some fuel delivery reduction...in terms of volume.....needs to be done. The way I do this is to adjust the spring loaded screw and unload it, undo it so that there is much less travel on the swing arm on the bottom of the bowl/accel. pump. The effect is to use only a percentage of the volume of fuel stored in the diaphragm. This is not the way Holley will tell you to set it up. You'll find a point at which too little fuel is delivered and a bog or hesitation will be felt. To correct for this, screw back in the spring loaded bolt a few turns and compress the spring a little. Try your engine/car again. Driving is the best measure, to see if the setup is working properly. Winging the throttle in neutral isn't the answer.

    I change my secondary springs. I start with the heavy black one and work, one at a time, progressively lighter, until I feel a bog or sag again. Then I swap back to the one before it that doesn't sag....all done. That's pretty easy to do. Your secondary carb tune may effect your mixtures, so I suggest you get a WBO2 sensor with data logging and do some freeway cruising and accel testing. Even though you may not feel it, the mixtures may lean or richen out and that may suggest that some larger or smaller secondary jets may be needed. Data logging will allow you to go home and sus out whats going on without fear of having a crash whilst driving, checking this, looking at that etc.

    Get to it..have fun
    '78 280C sedan P30 Y70 L4N71B 4.11 H190 N/A A 'NEW" engine combination 131 rwhp.
    '71 240C coupe N42 NEW E88 FS5W71B 4.33 H190 Megasquirt V3.57 212 rwhp

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    Greetings again...

    Ya know, we seem to have gotten off azkyinc's original question. But since he's gone back to the 390, maybe some of this will help.

    So at this point my Z is actually running pretty good. Starts up with out problems. Idles fine. Decent accel. No major flat spots. I got my motorcycle carb synch tool out and used it to adjust the pilot screw settings. HUGE improvement in idle and off idle accel. Holley says adjust the pilot screws to max manifold pressure. Damned if that didn't work. Was able to adjust idle after that as well (then re-tweak pilot screws). With that done I switched over to the white cam for the accel pump. The Holley flow curve says the total volume injected is lower than the Orange cam that came stock but more than the black cam I tried. Less flow at bottom part of curve with more flow at the higher part of the curve. Seems to work just fine. Oh... and I'm still running the 49 main jets (stock from factory was 51). Have not tried different squirters yet. According to Holley, my carb came stock with the smallest size available. So it's all up from here. I'll keep tinkering for a while and see what happens.

    I even washed the windows today so I can see out of the thing...

    Later

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    Keep in mind the small squirter does not inject less fuel, it injects fuel over a longer period of time. A larger squirter will dump the same volume of fuel faster.

    Happy tuning.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Quote Originally Posted by Zedyone_kenobi View Post
    Keep in mind the small squirter does not inject less fuel, it injects fuel over a longer period of time. A larger squirter will dump the same volume of fuel faster.

    Happy tuning.
    Exacto!
    '78 280C sedan P30 Y70 L4N71B 4.11 H190 N/A A 'NEW" engine combination 131 rwhp.
    '71 240C coupe N42 NEW E88 FS5W71B 4.33 H190 Megasquirt V3.57 212 rwhp

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    Quote Originally Posted by 5thhorsemann View Post
    Agreed, you're cheapest, fastest and best end result is to go with a set of stock SU round top carbs. Have never heard anyone say they have a reliable 4BBL driver.
    I know this is an old thread but you've heard it now. I took the SUs off mine years ago and put the Arizona Z and 390 on mine. It took a little bit of tuning (with an O2 sensor) to get right but it starts up as soon as I turn the key, no flat spots and good power.

    And as for the comment about no 90* manifold on a straight motor, ever think that most carbureted v8s have two 90* turns?

    So if anybody has a 4bbl set up they just can't stand, let me know. They work like a champ.

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    Quote Originally Posted by clutchdust View Post
    And as for the comment about no 90* manifold on a straight motor, ever think that most carbureted v8s have two 90* turns?
    Ok. That's not a good thing.

    It "works", but it doesn't mean there isn't something better...
    2/74 260Z

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    Well, V8's are more of a 45 degree slope... if you want to get picky
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    The absolute best you can do in terms of intake design is a straight shot into the valve, especially for a wet runner design such as any carburated manifold.

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    2/74 260Z

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    True Leon, I agree with you with what you say. Nice pics too btw.

    I like my Arizona manifold because it helps boost throttle response and low rpm torque in my engine. For my streetcar, the two small primary throttles help with fuel economy because they can be jetted that way. The secondaries can be tuned richer for a more powerful top end. The manifold divides the engine cylinders into two groups which allows a unique manifold resonance. This resonance boosts cylinder filling of air/fuel mix at low engine speeds.

    The floor of the arizona manifold is 90 degrees to the downward flow of the air/fuel mix coming out of the carb. Most street V8's running a four barrel carb will have a manifold floor that is also at 90 degrees to the flow out of the carb. Whilst not optimal for a RACE motor, its more than acceptable for a STREET motor. Just ask Ford, GM, Chrysler etc. An acceptable compromise, especially when there may be other positive attributes which will sway the decision not to use a race style induction on what is predominantly a street driven car and one that I'm very happy to live with.
    '78 280C sedan P30 Y70 L4N71B 4.11 H190 N/A A 'NEW" engine combination 131 rwhp.
    '71 240C coupe N42 NEW E88 FS5W71B 4.33 H190 Megasquirt V3.57 212 rwhp

    'Nissantiques - join the club'

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    Quote Originally Posted by ozconnection View Post
    True Leon, I agree with you with what you say. Nice pics too btw.

    I like my Arizona manifold because it helps boost throttle response and low rpm torque in my engine. For my streetcar, the two small primary throttles help with fuel economy because they can be jetted that way. The secondaries can be tuned richer for a more powerful top end. The manifold divides the engine cylinders into two groups which allows a unique manifold resonance. This resonance boosts cylinder filling of air/fuel mix at low engine speeds.

    The floor of the arizona manifold is 90 degrees to the downward flow of the air/fuel mix coming out of the carb. Most street V8's running a four barrel carb will have a manifold floor that is also at 90 degrees to the flow out of the carb. Whilst not optimal for a RACE motor, its more than acceptable for a STREET motor. Just ask Ford, GM, Chrysler etc. An acceptable compromise, especially when there may be other positive attributes which will sway the decision not to use a race style induction on what is predominantly a street driven car and one that I'm very happy to live with.
    Sure, as I've said, it "works". While you may understand the ramifications, others just don't.

    However, I'd be surprised if there was much of a positive resonance effect with that manifold. With the runners having different lengths, resonance will happen at various engine speeds when looking at different cylinders. This means that while 2 and 5 are in resonance, 1 and 6 are already past the peak and 3 and 4 are coming up to it. FWIW, you can tune pretty much any system for fuel economy at part-throttle and a powerful top end, it's not unique to 4-barrels.

    With that said, I'm hoping my next major project will be a V8 with ITBs. 1UZ looks tasty...
    2/74 260Z

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    The Arizona isn't a bad effort really, the runners may not be all the same length as you've noted but they do 'tune' themselves at a number of different rpm's that way. There is a comparison to exhaust headers here. Tuned length promote high end power at a particular rev range. (ie triple weber individual runner manifold) Interference, by design, don't offer a power peak as such but a spread of power over a somewhat larger and lower rev range. (ie Arizona four barrel manifold)

    Race vs street setups.

    Agreed, most performance carbs can be tuned to offer the best of both worlds to some degree. I just don't hear too many people tuning their triples for economy!

    Having, in effect, two carbs in one body just lends itself so easily for this kind of calibration.
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    Quote Originally Posted by ozconnection View Post
    The Arizona isn't a bad effort really, the runners may not be all the same length as you've noted but they do 'tune' themselves at a number of different rpm's that way. There is a comparison to exhaust headers here. Tuned length promote high end power at a particular rev range. (ie triple weber individual runner manifold) Interference, by design, don't offer a power peak as such but a spread of power over a somewhat larger and lower rev range. (ie Arizona four barrel manifold)

    Race vs street setups.
    Right, an intake and/or header can be tuned for any rpm you want, length depends on which rpm and harmonic you're shooting for (usually 3rd because of packaging limitations). A longer manifold will be "tuned" at lower rpm and a shorter manifold at higher rpm. The bandwidth and magnitude can be altered by varying taper. This can include built-in taper and/or air horns. In the case of a header, "steps" are also sometimes used.

    Having different cylinders hitting resonance at different times is not buying you (as) much.

    Quote Originally Posted by ozconnection View Post
    Agreed, most performance carbs can be tuned to offer the best of both worlds to some degree. I just don't hear too many people tuning their triples for economy!
    I am.

    Quote Originally Posted by ozconnection View Post
    Having, in effect, two carbs in one body just lends itself so easily for this kind of calibration.
    Most carbs have circuits, which can be tuned individually and somewhat independently (e.g. idle circuit doesn't really affect WOT main circuit). There is no reason that a carb can't maximize mpg and power to its utmost potential, unless something went terribly wrong with that carb's design.

    If you're interested, I've made a few somewhat in-depth posts on intake and exhaust runner design:
    Intake
    Exhaust
    2/74 260Z

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