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Thread: Installation Of Round Tops In A 73 240

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    Default Installation Of Round Tops In A 73 240

    HELP PLEASE. I purchased a set of round tops and the intake manifold to replace the flat tops on a 1973 240. Disassembly and removal is not an issue. However replacement is where I am getting stumped. All of the pluming that was on the old carbs, along with the smog stuff is getting me confused. Is there a source that has a step by step or at least some hints as to what I should so with all the connections that I no longer will have when I install the new manifold and carbs. Is this really more complicated then I first thought. I have the knowledge to tare the motor down and rebuild it but I have never dealt with carbs and carb systems.

    Zippy
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    Default another photo

    engine compartment
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    Can't help you with a step by step, but the pic of your new carbs/manifold is missing the smog equipment that it came with from the factory.

    I think I would just block off (plug up) anything that I didn't have a place to connect on the new manifold.

    One other thing, I doubt that you will be able to use the carb operating linkage that is currently on your car when using the new manifold. Lenght of the linkage is different between Flat-tops and Round tops.

    I'll try to get a pic of a Round Top set-up with all the "normal" equipment attached later to day for you.
    Last edited by Bambikiller240; 06-11-2004 at 08:57 AM.

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    Start by removing all that smog stuff that is attached to the 73 intake manifolds (most of it probably doesn't work anyway). Now you will hear that the 73 manifolds are better than the previous years but this is not proven and up to you. You won't need the air pump either (this is the pump on the drivers side of the engine and it has a hose that runs up to the exhaust manifold) but that is up to you if you leave the original exhaust manifold with the backfire valve attached. Or you can plug the gallery to prevent exhaust from coming out.

    When you attach the new manifold the only attachments you really need is the vacume for the brake booster and the vacume for your vacume advance.

    The rest of the carb attachments are pretty easy. Float bowl vents to the air intake box. Valve cover vents to the center of the air intake box. PCV valve to the block.

    Plug the water that runs through the manifolds. If you plan on using the water passages then make sure the freeze plugs under the manifolds don't leak. Also the tube that connects the two manifolds.

    Like Bambikiller said make sure you have the correct throttle links or you will be stuck. The 73 links will not work.

    Good luck.
    The 1973 240Z 165540 Slightly modified. L28, 5sp, cam, headers, MSD 6AL, power windows, power door locks, leather seats, custom this and custom that.

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    Depending on your states emissions requirements for older cars, you may "need" the smog pump. So before you toss this stuff out in the garbage you might want to confirm what the requirements are in VA



    BTW, many people say to toss all the smog stuff out because it probably doesn't work anyway, (NOT pik'n on you Ed, heard it many times in many places) well I just finished a complete rebuild of my 72 L24 enigne and have bee messing with the smog equipment. I replaced the vacuum hoses only and after blitzkraig tuned my carbs another friend offered to put the car through a smog systems check ( for free and not reported to the state) and the car passed with flying colors.

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    Default thanks all keep it comming

    Thanks all, I still could use all your comments, keep them comming.
    Last edited by alordzot; 06-12-2004 at 03:30 AM.

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    I'm at a loss for words,I did this swap myself and it is easy once you rip everything off the motor so you can see what the hell your doing wish I could tell you how to do it
    Last edited by xbox; 06-12-2004 at 03:01 AM.
    fluffy

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    Default Linkage

    Ok if the stock linkage is not going to fit where can I get one that will. Does Ztherapy sell them?

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    Have you tried to get the linkage from where you got the carbs?
    The 1973 240Z 165540 Slightly modified. L28, 5sp, cam, headers, MSD 6AL, power windows, power door locks, leather seats, custom this and custom that.

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    Carbs were purchased on ebay. so No access to them.

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    if you look at the firewall linkage theres about an inch or so extra rod I wonder if the flange can be ground off and rewelded so it will work?
    Last edited by xbox; 06-12-2004 at 09:23 AM.
    fluffy

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    Try posting in the wanted section maybe someone has one laying around.
    The 1973 240Z 165540 Slightly modified. L28, 5sp, cam, headers, MSD 6AL, power windows, power door locks, leather seats, custom this and custom that.

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    the difference is that the linkage rod that connects the two carberators is too short. If you cannot come up with one from a bone yard or someone on this site get back to me I know a guy that might have one , it's just that he is hard to contact , but let me know . Gary After thought, I wouldent remove the '73 manifold if were me . There is nothing to gain by making the change. Just strip off all the unneeded stuff . You need to use the spacers from the round tops that are thicker that your old ones. Also the earlier air cleaner box. You can plug the large inlet from the air pump like was said before all that is needed is the vacume line to the brake booster and the carb vacume to the advance on the dist.
    Last edited by beandip; 06-12-2004 at 01:39 PM.

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    I did the conversion this summer. I got the carbs only and put them on the old manifold. Block off all water passages. Surprisingly, all water passages I found to be NPT (national pipe thread) fittings. Blocked everything on the manifold except PCV valve hose and vaccum to the brake booster. You will need a new linkage that you can get from Z Therapy for something like $15.

    Fuel mileage went from about 14 mpg to what I think is a very credible 19 mpg around town and 30-31 on the highway. I was pretty shocked by these numbers, but they're very consistent.

    The other thing I've found to be surprising having read other posts is that I've never had a vapor lock issue. It's not unusual for it to be 100-105*F here and the car has performed flawlessly this Summer. I don't have any insulation whatsoever on the fuel lines either.

    You'll like the improved driveability after changing over to the round tops.

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    Is the manifold from the 1973 240Z the same as the one in the 260Z w/ the flattop carbs? If so, won't he need to use the thinner spacers because the studs on the 260Z manifold are shorter, or do like I'm doing and swap the studs from the early 240Z manifold? I tried my early carbs with the shorter studs, but just barely got the nuts threaded on. Bought some of the thinner spacers, but decided to just swap studs and use my old thicker spacers. I'll post a couple pics with the carbs mounted on the N36 Intake from a 260Z to show how the nuts barely thread on to the shorter studs. Anyway, if the 73 manifold has the longer studs my question is moot. Gary
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    1970 240Z - 7/70 HLS30-07273
    1971 240Z - 12/70 HLS30-17821
    1972 240Z given away, then went to crusher
    1983 280ZXT sold to finance 1970
    1992 Chevy Shortbox K1500
    1999 BMW R1100GS

    Rust Never Sleeps

    Neil Young

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    My car currently has a single downdraft carb on it off a Cedric or something similar. I have two sets of SU's and want to fit one of them. One of which I think is a set of 'round tops'. Which one of these should I use:
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    I'd use these : http://www.classiczcars.com/forums/a...achmentid=7806

    The others are BOAT ANCHORS

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    what service! thanks for that

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    remedy, i don't speak from any position of authority on this issue but if you go to the ztherapy website and look up their carb information they say that first set (w/o air filters) are only good for wheel blocks. you should probably ask bruce. i think the site is www.ztherapy.com. but if that doesn't get you there, you should be able to find it through a search.

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