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Thread: Carbs

  1. #1
    Registered User sapruns's Avatar
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    Question Carbs

    Can anyone tell me how to adjust the SU carbs to get the best performance out of them?
    Any tricks or tips in doing this?

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    Registered User biker's Avatar
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    Default

    Get someone else to do them


    Seriously, it will all depend on what configuration you are running. If I follow the book, mine will run like a pig as I am running a cam and advanced timing. It states that you need one turn on the screw underneath. I found that mine will run better with two turns.

    I think it is also essential that you get a balancing tool to get them right. Once you achieve this, car will run nice and smooth


    Biker
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    Registered User biker's Avatar
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    Just another word of advice

    If you start adjusting things such as balance, air mixture, etc, take a note on where the settings are before you start e.g screw in mixture nut but count the turns until it is seated.

    If things go wrong, at least you can get it back to where you started


    biker
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    Registered User sapruns's Avatar
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    I thought about what you said so I decided to talked to the guy who rebuilt my engine. He has a ballancing tool and is familiar with dual carbs. He new what was needed when I told him how it was running. He wasn't the one who took the engine out or put it back in, he only rebuilds but offered to set the timing and adjust the carbs for me at no additional charge.
    He use to own a Z long ago so I think he enjoyed working on mine.
    Thanks for the help

  5. #5
    beandip beandip's Avatar
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    Default adjusting round top SUs

    If you decide to learn how to adjust them E-mail me and I can walk you through the procedure. There is a tape available still I believe on this and other things at Z Therapy . They are the best source .

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    ZCOOR #109
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    Yes
    You want to acquire the video from ztherapy.com. It is detailed and complete.
    Remember, the engine must itself be in tune to tune the SU's.
    Start with a good valve adjustment, then plugs, points, timeing.

    Then set the mixture of the needles, after checking the chokes release freely. All this is done with the air filter removed along with the filter cover.

    THE ADJUSTING OF THE SU'S IS A REPETATIVE PROCESS.
    That is to say, you gradually close in on a fine tune.
    Consider getting a color tune device/ and/or use a sensor in the tailpipe for air fuel mixture.

    buy a book covering this procedure, take notes when viewing the video tape of Ztherapy.
    Good luck.
    Lowell
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

  7. #7
    Registered User sapruns's Avatar
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    Exclamation

    I found a guy, next town under/over who restores old cars. He’s familiar with the dual carb process and has the equipment as well.
    He is going to show me how to do it the first time so I’ll take good notes but I like the idea of this video. If you own a Z you should have the tools and documents to maintain it.
    I will get the video and start looking for the gages/tools to adjust the carbs. Thanks for the feedback. If you know where I can get these gages, let me know.
    Thanks again,
    Ken

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    Registered User MikeW's Avatar
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    Default

    Originally posted by sapruns
    If you know where I can get these gages, let me know.
    MSA sells both the Synchrotester and the Color Tune:

    http://www.zcarparts.com/store/merch...tegory_Code=TE
    -Mike
    Add your Z to my online spreadsheet registry

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    beandip beandip's Avatar
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    Default tools to tune the carb

    I bought my colur-tune from r.d.enterprises www.rdent.com ray had the best prices. I bought the uni-sun to ballance them at the local parts store , go to the performance section. Edelbrock made mine. $25.00 . the uni-sun is a must the colur-tune you can do with out.It is a good tool and one you will use, but if cash is tight you can do without it , it just saves time . The reason that the adjustment biker was talking about was so different is that most likely the throttle shafts are leaking air due to ware either that or a vacume leak.

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    Registered User biker's Avatar
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    Hi Beandip

    If I am suffering from too much air getting past worn parts, how can I check this?

    Carbs seem to run pretty good except I do get a bit of gunk down around the rubber hose from the bowl to the Carb. Probably seeping fuel that picks up road grime.

    Does anyone in Aus know where you can get a colurtune and what is the cost of these.

    Thaknks in advance

    Biker
    Spending too much again!

  11. #11
    Registered User MikeW's Avatar
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    Originally posted by biker
    If I am suffering from too much air getting past worn parts, how can I check this?
    Biker
    Scott Bruning in his tune-up video mentions just slapping some grease at the end of the worn shft as a way of reducing the air leak.
    -Mike
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    Registered User biker's Avatar
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    Default

    Thanks Mike
    Spending too much again!

  13. #13
    beandip beandip's Avatar
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    Default some heavy grease

    putting some heavy grease around the throttle shafts ends and where they extend out the side of the carb should show the difference , another way to find a vac. leak is to spray around the carb with carb cleaner with the engine warmed and running and you will see a change in rpm when you hit a leak. less of a mess. I dont want to deminish the good of the color tune , I use mine and I think that it is great , and it lets you see what is happening at upper r p m . and you can varify what you have adjusted the carb to. rich or lean. Come in real handy when trying different needles , you can see the flame in the chamber up to 3000 RPM .

  14. #14
    Registered User sapruns's Avatar
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    Default carbs

    I got the video and it was good, it really helps.
    I got the synchrotester and was able to adjust the carbs, not too difficult, it actually runs good.
    I just got the car painted, original blue for the 71's, #TB903.
    Ill post it once all the pieces are back on and the windows are in.
    Thanks for all the help.

  15. #15
    Registered User sapruns's Avatar
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    Default carbs

    Any of you who have used a color tune, how does it work?
    Can you adjust both carbs from one plug or do you need to use all six? Is it worth buying one or do without?
    I got the video from Ztheropy and it was very helpful. The syncrmeter was fun to use and it worked out well.
    Thanks for the feed back in advance.

  16. #16
    Registered User MikeW's Avatar
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    Default Re: carbs

    Originally posted by sapruns
    Any of you who have used a color tune, how does it work?
    Can you adjust both carbs from one plug or do you need to use all six?
    I'm thinking about getting one myself. Surely you'd have to use at least two plugs, one from the front 3 and one from the back 3. If you did all 6 and there was a difference between, say, #1 and #2 I don't see how you could adjust that apart from modifying the intake manifold. However, all cylinders sharing the same carb should have the same mixture.
    -Mike
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    ZCOOR #109
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    The colortune is used in the # 2 and @ 5 cyclinder in place of the regular plug. These are the "center" cylinders that are fed by each of the carbs, thus they would have the "ideal" mixture that is being spread to three cylinders. The goal is to get a mixture that is ideal. The "ideal" would burn a certain color. there should be a color chart with the tool.
    The thought is there would be a slightly different mixture to the "end" cylinders, the ones that are farther from the carb along the path of the intake runners.

    Again, set the colotune/mixture, then the balance/unisyn, then the mixture then the balance. They influence each other somewhat, thus the repetition.
    Years ago, we also used a set of wire deals that were bent at 90deg and faced each other.They fit into the top of the carb after removeing the oil cap. As the throttle was opened, you watched the wires to see them move in unisyn as they rode on top of the carb piston. The unisyn air flow does this at idle, but does not show the movement of the carb pistons together under various throttle openings..... whatever.
    good luck
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

  18. #18
    Registered User mdbrandy's Avatar
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    Originally posted by Lowell Marx
    The "ideal" would burn a certain color. there should be a color chart with the tool.
    For any of you that have actually used the colortune, what colors do you have to be able to see, and how close is the variation? I ask because I have a very slight red-green colorblindness. I can see red and green fine, but very light shades of red I can't, and two shades close together that other people can tell apart, I can't. Thanks Mom.
    Mark Brandyberry
    1970 240Z (11/69) HLS30 00215
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    IZCC #802 & CZC#4028

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    Registered User MikeW's Avatar
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    Default

    I'm not sure but I suspect the correct mixture results it's a blue flame similar to to what you'd see on a natural gas stovetop. Sometimes with those you'll see mostly blue flame with wisps of yellow/orange. If you can differentiate between those you'll probably be Ok with the colortune.
    -Mike
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    Registered User sapruns's Avatar
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    Talking

    Thanks for all the input. Ill let you know how it turns out when im done.

  21. #21
    ZCOOR #109
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    You only need one colortune device!

    Use on one carb at a time to set mixture. That is to say put in the #2 cylinder, adjust the mixture nut on the bottom of the carb, remove and put in #5 and do the adjust. Then set the idle and balance with the unisyn on the face of the velocity stacks of the carbs. Then use the colortune again to check mixture, etc. etc.
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

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    Registered User tanny's Avatar
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    Just a note. I have triple webers and was unable to get the unisyn to register anything at all at idle. Has anyone else had this problem? After adjusting the mixture by ear, I used the colortune to check and was very close to optimal. Victor.

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    Registered User MikeW's Avatar
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    Originally posted by tanny
    Just a note. I have triple webers and was unable to get the unisyn to register anything at all at idle. Has anyone else had this problem?
    Your unisyn "wheel" is closed all the way and the marker still doesn't float?
    -Mike
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    Talking Recently Purchased a Unisyn.

    Hi guys good topic here. I bought a Unisyn recently and haven't had a chance to use it but I was browsing the Ztherapy site and curious about the SM needles they have.

    My current engine setup consists of the following:-
    F54 Block
    E88 Head (With Larger ZX Valves).
    Mild Cam.
    Extractors Etc..
    Electronic Dizzy.

    I get pinging on WIde Open throttle or when i give it a bit of stick depending on a few things and I think the car runs better if the choke is out for higher rev driving.

    I was planning on gettin her on the Dyno and having it adjusted properly by an expert but do you think that the SM needles will work provided I tune with the Unisyn?

    I haven't got a colortune kit and have no idea where to get one, I guess I'll ask around for that.

    Any help appreciated.

    Also can anyone stand by Ztherapy there info is impressive but I'm not sure if my carbs need to be rebuilt or not. THey seem ok apart from the issue mentioned above.

    Thanks.

  25. #25
    Registered User civ104's Avatar
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    Default

    I'd be happy to recommend Z-Therapy. Their rebuilt carbs are as good and pristine as they say and their service is excellent. I couldn't be more satisfied with the set I got from them.
    Chuck Vigdor
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    1N48A41E97C801614

    "Das was mich nicht tötet, macht mich stärker." (that which does not kill me
    makes me stronger)

  26. #26
    Registered User tanny's Avatar
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    mikew,

    Yes, I adjusted the wheel from totally open to closed and still the marker wouldn't rise. The marker seems to be free of any undue friction, so I think the unisyn is working. I wonder if anyone with triples has had this problem. Thanks, Victor.

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    Deftly daft Alfadog's Avatar
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    Default

    How much $$$ would one expect to pay for someone to rebuild some SU carbs?

    Just roughly..

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    Registered User sapruns's Avatar
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    Default carbs

    Well I got my color-tue and tried it out. My carbs were way out of adjustmet according to the color tune. I started with cylinder # 2 and 5 (at 800 rpms idle)and got it to a bunsen blue but it hesitated a little when I drove it. I tryed it again but increased the idle to 1000 and then adjusted it again and it made a big differance. Does this sound correct? After all that I checked the idel using the syncrometer and did a final adjustment. Learning how to maintain your of car using the right tools rather then relying on some one else is alot of fun.

    To change the subject a little, if I wanted to replace the stock air cleaner with the K&N or Ramflo, what do you do with the two hoses to the carbs as well the one to the valve cover and engine block ect? No sure I want to go this route but it may it seems as if it would improve the air flow. Any advice would be appreciated.

  29. #29
    ZCOOR #109
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    You can change the filter element but do NOT change the "back plate" that bolts to the carbs. It includes the "air horns", the metal tubes that the air passes through on the way into the carbs.

    The air horns are essential to the efficient operation of SU type carbs. The backplate may be removed if separate airhorns are acquired and mounted. But then how do you mount the new air filter?

    Then,...
    Try fitting a remote cold air induction CAI up to the air filter box opening by some form of customizing. Then remove the orginal filter from the airbox, using the filtering of the CAI.

    Note, an air box is also a key in appropriate performance of SU type carbs. Air tends to pass by the airhorns during highway speeds, not "making the turn" into the airhorns.

    Just be sure that the lever on the air box is set open for summer, and you will get plenty of air to the carbs for a stock engine. If you have significant performance work inside the engine where it needs to "breath" a lot more air, then work the CAI deal by doing some engineering as previously stated.
    Good luck,
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

  30. #30
    beandip beandip's Avatar
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    install a K & N filter in the stock air cleaner box and the engine will perform better . The individual K & N cone shaped filters look real good but dont perform as well with out the stacks that are on the stick cleaner. As was stated before unless you are running a big cam and a stroker , you would then be running tripples, you have the set up that will work the best right now. You might look to SM needles for the 280 engine , they deliver more fuel at higher RPMs and run great at normal street Rs. just a different taper. NOTE !! New information is that the SM needles are not advisable on a Z application . They are so rich they will cause the oil in the cylinders to be washed away and premature engine failier will result. I tried them on avice from supposidly a person of knowledge. I have since found other wise. Gary
    Last edited by beandip; 08-07-2005 at 04:58 PM.

  31. #31
    Registered User sapruns's Avatar
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    I ended up doing what you suggested by getting a K&N filter for the stock housing. Its a little expensive but im told its a life time filter. They show you how to clean it for re-use. I like this setup better then modifting what I have.
    Thanks for the input.
    Cheers

  32. #32
    Formerly Datto-Zed Murph's Avatar
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    How detrimental to performace is having the stock airbox removed along with the horns, just aftermarket pod style filters in their place?

    That's the sorta set up on my zed (as I bought it). Would it be worth while fit some aftermarket horns?

  33. #33
    Formerly Datto-Zed Murph's Avatar
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    Does anyone have any photos of the stock horns?

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    Default carbs

    Gav240z

    You are running lean or your running too much advance on your timing. Either way your on a fastrack to disaster. Check timing first (The cam co. sometimes specifies timing ). Then richen up your carbs by raising your needles. Ping is the enemy if you can hear it then you know one these conditions exists. Besides nothing uglier than piston ate up by detonation.

  35. #35
    Registered User mdbrandy's Avatar
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    Default

    Originally posted by Datto-Zed
    Does anyone have any photos of the stock horns?
    Do you mean this?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	stockcarbplate.jpg 
Views:	89 
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ID:	2786  
    Mark Brandyberry
    1970 240Z (11/69) HLS30 00215
    1978 280Z (05/78) HLS30 466356
    IZCC #802 & CZC#4028

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    That's the one mark! Thanks for that....much appreciated.

  37. #37
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    Ztherapy has air horns for sale as I remember.

    You still are going to have a difficult time finding adequate air filters, or how to install them on naked airhorns.
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

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    Hmm..... I think I'll worry about it when I get the thing back on the road.

    Any idea what sort of performance hit we're talkin for not having the horns on?

  39. #39
    ZCOOR #109
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    Can't give you any real numbers. Just the fact that the smooth flow of air to the carb has been documented over the years with thousands of competitors and manufacturers developing the airhorns.
    You need to get ahold of and view Ztherapys video on the SU. It is an excellent document on repair/rebuild and adjustment of the carb. as it applies to the Datsun Z car.
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

  40. #40
    Wanting his Z on the road SuDZ's Avatar
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    Is the Ztherapy a good video for a begginer? I have not really gotten into carbs before so I am a newbie at them. Would you say that the Ztherapy video is good for me or is it more advanced?

    SuDZ
    1974 260Z - A work in progress
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    ZCOOR #109
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    If you have never touched your SU's you will have to watch the video, then work on the SU, then watch the video. Doing this several times. The video is totally detailed. The situation is there are a number of facts to understand and remember. You have to start somewhere.

    Unless you learn the carb, you will have to depend on others to adjust the carbs. That is problematic, there are few who do. It is just about a certainty that no Nissan dealer has a tech that can even say SU, let alone work on one.

    If you own a Z with SU's then you need to learn to adjust and do basic maintenance such as removing the piston, adjusting the needle, etc. and of course using a unisyn to balance the two.

    You only need to stand over the SU for a 30 minute period, trying to memorize the pieces. Then watch the video, then go work on the things.

    Good Luck.
    Lowell
    original owner 72-240Z
    Original Blue w/White, 79,000Miles

  42. #42
    Wanting his Z on the road SuDZ's Avatar
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    Originally posted by Lowell Marx
    If you have never touched your SU's you will have to watch the video, then work on the SU, then watch the video. Doing this several times. The video is totally detailed. The situation is there are a number of facts to understand and remember. You have to start somewhere.

    Unless you learn the carb, you will have to depend on others to adjust the carbs. That is problematic, there are few who do. It is just about a certainty that no Nissan dealer has a tech that can even say SU, let alone work on one.

    If you own a Z with SU's then you need to learn to adjust and do basic maintenance such as removing the piston, adjusting the needle, etc. and of course using a unisyn to balance the two.

    You only need to stand over the SU for a 30 minute period, trying to memorize the pieces. Then watch the video, then go work on the things.

    Good Luck.
    Looks like I will be adding them to my list of thigns to pick up then.

    SuDZ
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  43. #43
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    Ya, That tape is pretty dam good stuff. A little disjointed at times, where he forgot to mention something and had to back-track. Have paitence, watch over, I know it's long. If you fall asleep during one part, it's very much to your benefit to watch that section over again.

    If you own a Z, 510 or Roadster, it's a "must watch"
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    I bought some 71' SU's off of ebay for cheap and they came with the Z therepy video. Helped a lot when I tore them apart and rebuilt them. Unfortunately, I wasn't very careful with the needles and ended up marring and bending them. Mostly because they were stuck in the jet nozzles. I got the carbs to run, but they were very hard to adjust.

    There were a few things I don't remember the Ztherepy mentioning. Like making sure the plate that sits under the adjusting screw that controls the butterfly opening can touch the screw as it is screwed in. I don't remember if he mentions that when the choke is pulled out all the way that the butterfly should be somewhat opened either. I fixed both of these problems and I replaced my needles with the Ztherepy SM needles. They run better than they ever have before, but they don't balance well. At low RPMs the rear carb flows less than the front, and at high RPMs it flows more. Not too much of a varience, and the idle is smooth, so I'm not complaining for now. I'll try watching the video again and see if I missed anything.
    Alien-E : 1973 240Z

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