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Thread: SU carb engine with a L28

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    Default SU carb engine with a L28

    Sorry guys I been reading on the SU and I cant seem to find it or didnt recognize it but here is my question.
    I have a L28 engine on my 73z and I had tripple carbs but Im converting back to SU
    Will the Su work and if so what do I need to do to make it work for a higher liter engine?
    Im just tired of tripple weber carbs and they are very sensitive that I keep adjusting. I just want SU now and I dont race so its a waste to even have tripple webers if im just dailing driving it.
    I like having good gas milage as well and tripples dont do that for me.
    Thanks everyone for being patient with me and answering my question on this. Really appreciate it


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    I had an L28 EFI engine in my '73 240Z that had the stock 240Z SUs fitted to it.
    They worked very well and the engine responded excellently
    I don't believe you will have to modify the carbs. at all, just make sure the fuel supply pressure is correct and use a fuel return line to avoid vapour lock in hot weather.
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    They will work fine. We have had 2 different Zs with 2.8 engines with our standard production carbs holding hillclimb records locally.

    If you get 'em on and running and they are lean you might want to throw a set of SM needles at them.....
    Bruce Palmer
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    SM needles may be too rich, depending on the rest of the engine mods and your altitude. Of course, if you were running triples, the engine may be able to use the richer mixture of the SM needles.

    I know several people with SUs on L28s, beandip is one. Seem to work great.
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    You guys are great. I really appreciated it.
    SM needles? Ill take a look at those.
    I really love this car club. Alot you guys have been very helpfuly.
    Is there a site for these SM needles and how big do I have to go?
    Im running a mild cam on my engine but nothing major after that
    Last edited by myfairlady; 06-05-2009 at 08:27 PM.

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    We should see if we can get Gary (beandip) to chime in. He has an L28 with P79 head and a mild cam and header, found the SMs were too rich for his setup. Can't remember what he ended up running, I think it was the needles for a '70, which were the richest of the stock 240Z needles.
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    beandip beandip's Avatar
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    I am indeed running SUs on a ZX motor as Arne stated. The compression is at 9.5 to one . Not high but higher than stock. When I installed this engine I thought because of the headers , Cam and larger displacement I may need richer needles . I tried the SMs and they caused the mileage to tank and were so rich that I was getting gas in the oil . I tried the 47s I think that is the number. In any event the ones for the '70Z that Arne mentioned and again vary rich. I went back to the needles that I was running on the L-24 Motor and she runs well . I tried 58s also, too lean. I bought a new set of 54s and have been running them for 8years +. Good torque all through the power band. Mileage is good too and I can run regular gas but use the midrange gas. Aside from the good performance. I took the Z to the Emissions center , DEQ here in Or. and the car passed emission testing. '73 is exempted but since it was a free test I thought I would do it for me. I have zero emissions equipment on the car.
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    Last edited by beandip; 06-05-2009 at 09:22 PM. Reason: spelling
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    Quote Originally Posted by beandip View Post
    I am indeed running SUs on a ZX motor as Arne stated. The compression is at 9.5 to one . Not high but higher than stock. When I installed this engine I thought because of the headers , Cam and larger displacement I may need richer needles . I tried the SMs and they caused the mileage to tank and were so rich that I was getting gas in the oil . I tried the 47s I think that is the number. In any event the ones for the '70Z that Arne mentioned and again vary rich. I went back to the needles that I was running on the L-24 Motor and she runs well . I tried 58s also, too lean. I bought a new set of 54s and have been running them for 8years +. Good torque all through the power band. Mileage is good too and I can run regular gas but use the midrange gas. Aside from the good performance. I took the Z to the Emissions center , DEQ here in Or. and the car passed emission testing. '73 is exempted but since it was a free test I thought I would do it for me. I have zero emissions equipment on the car.
    Gary
    Beandip.

    Thanks for all the info. Your lucky there is no emissions in your state. In my state even though its a 73 it has to be a 68 to have no smog. Suck especially when I had tripple carbs but cause of the info on the SU's Its going to be worry free for me now. Mid grade huh? awesome. I been running high oct cause the tripples are picky.
    So 54 is the stock needles for these carbs? The carbs im getting is from a l24.
    Im running a mild cam and a 6 to headers so these carbs are great for the spec I have now.

    Thanks alot everyone I cant stress enough how you guys are helping me out and really appreciate it

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    The story on the SM needles is as follows: In the 7-73 book "How to modify Datsun engines and chassis" the SMs were installed as part of the first step up in performance tweaking. They tend to overcome what some believe to be a lean condition in the stock needles (some being worse than others).....

    As has been stated here, getting one needle or another to run well seems to be engine dependent....
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    I will be getting my carbs in two weeks. If I need the sm needs where do I get it?

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    I got SM needles from ztherapy.com 3 years ago works well on my L28,

    check Bruce Palmer signature on previous reply

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    Does your engine have any other modifications, or is it basically a stock L28?

    I'm running modified original SU carbs on my car and don't have any complaints. Mine is a F54 on the bottom with a ported and polished P79 on top. I opted to get some more flow through the 'ole SU's.
    I sent them to Rebello and had the carbs overbored with custom tapered needles made for my application. After I got them back it was a simple bolt on affair. The only adjustments I had to perform were airflow syncing and hooking up my wideband O2 sensor to dial in the A/F mixture to optimal. They have worked great ever since.
    Last edited by blue 72; 06-08-2009 at 04:51 PM.
    '72 240Z - F54, P79, '78 5 Speed, 3.9 R200

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    Why did you feel the need to have the carbs massaged? Had you ever run fast enough to run out of carbs before? Just curious....
    Bruce Palmer
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    Quote Originally Posted by Bruce Palmer View Post
    Why did you feel the need to have the carbs massaged? Had you ever run fast enough to run out of carbs before? Just curious....
    Because I knew that it couldn't hurt. I didn't want to open up the airflow potential of the cylinder head, have a higher lift and duration cam installed, port match the intake manifolds, run an electronic dizzy, etc... and have an area of the total combination that could potentially be improved but had been left alone (I didn't go crazy on my build, but I wanted a fun car though). I weighed the option of going with triple Webers/Mikunis/Canons vs. overbored SU's and liked the idea of stock appearance and a slightly lesser financial outlay.

    I researched many similar setups, pored over much of the Z masters' leavings on the interwebs, and asked my head builder for recommendations. It was the conclusion that I came to for my particular combination of components.

    Right now it is a street car with future potential. I haven't had it to a track yet (suspension is next), so in no scenario have I run out of carbs per say. It is still going to take some fine tuning and fiddling before I find the next area that can reasonably be improved upon. I like the car the way it is now though. 7k+ rpm sounds great.

    I know ZTherapy has many years of experience building, customizing and generally fiddling with Skinners Union carburetors. I think I've read your opinions on the subject before and I don't want to sidetrack the thread too much, but what have been your observations of airflow potential through SU's with larger engine displacement requirements? Just out of curiosity.
    Last edited by blue 72; 06-09-2009 at 03:38 PM.
    '72 240Z - F54, P79, '78 5 Speed, 3.9 R200

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    Hey, thanks for this write up, since I'm getting ready to do the same thing to my 73.
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    Thanks for the info. My engine is just a mild cam and pretty much thats it. Since im not going to be doing any autox or circut racing anymore I dont need to built up the carbs. Thats why I sold my tripple webers. I just want to enjoy the nostalgic feeling of my z now with better gas mileage.
    Yes the sound of tripple carbs is pretty impressive but I like the sound of SU's as well.
    Cool I have a 73 as well 240zgl
    Last edited by myfairlady; 06-10-2009 at 09:27 AM.

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    Bottom line for this discusion from where we sit: 46mm Hitachis on a 2.8 motor is plenty of carb.... The several examples of 2.8 cars holding hillclimb records around here should point to the "enough carb" capabilities, especially if those looking to make the choice are running street cars. Two-eight motors in the heat of battle will use up more carb than a 2.8 on the street.
    Bruce Palmer
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    Well said... Ill keep you guys up to date when I put them on

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    I am turning on old, crusty '75 280Z I have into a 24 Hours of LeMons racer and I'm thinking of doing the same swap. The old FI system is likely going to require loads of diagnostic time and work since the car has been sitting for 17 years since it last fired. I have a '72 240 engine with SU's that also hasn't run in decades, but I figure SU's will still be simpler than FI for a LeMons race.

    What is the best thing to do for a fuel pump? I'm thinking an electric pump will be easier than making a mechanical pump work with the N42 head. Is there a cheap electric pump that anybody recommends? Years ago, I ran a Holly red on a triple Weber car, but it was obnoxiously loud. Not that it matters for a LeMons car, but I'd rather not listen to it for 24 hours.
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    Can't help ya on a pump pick, but do get yourself a bullet proof set up for controlling pressure out put. SUs wont take more than about 3 1/2 pounds of pressure before the needles and seats will be over powered and held open. At that point you can take the floats out of the float bowls 'cause theyza gonna fill up and runeth over.....
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    Thanks Bruce. I assume I want to run a return system?
    Jeff
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    Speaking of fuel pump. I notice I got one in the rear. Since im going back to SU set up do I need the rear electric fuel pump???

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    Jeff G, do run a return line. I have been running a RX-7 pump for 8 years now , from a '80 RX that was Carbed. Silent and supplies all the volume a triple will need on a stroker and will not over whelm a pair of SUs . At least I haven't found any trouble . There silent also.
    Gary
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    Ok guys I got the carbs installed. the exhaust feels if you put your hand near the pipe . Its pushing hard and it gargles. Im trying to tune them but does anyone have any advice what I should do???

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    Oh and another question... How much oil do I put in the SU carbs???

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    OK I figured it out. It doesnt gargle anymore. I took out the egr stuff and plugged up the three holes on the balance tube. Wow its very responsive and its more controlable in throttle. Im really glad I went to stock..
    second gear in low rpm is great. Doesnt feel like its dying. It's a very controllable and enjoyable ride now.

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    Hi,
    i am really agree with Bruce Palmer . He is saying correct thing. its nice to see.

    Thanks !!
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    Quote Originally Posted by Samuel View Post
    Hi,
    i am really agree with Bruce Palmer . He is saying correct thing. its nice to see.

    Thanks !!
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    Geeze - that grammer sure is familiar.
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    http://www.classiczcars.com/forums/s...t=31001&page=2 If you look at post 29 of this thread you'll see that the fuel air ratio of the SM's was almost perfect! The dyno operator commented that it looked like a fuel injected engine. Guy
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