I found a vacume leak at the base gasket of my front round top su
now i have fixed it my z wont run right it is like it is running on 5 cylinders
but no mater what lead i pull of it makes no diference, and it is blowing lots of black smoke i am guesing it is runing rich but i dont know how to lean it out? (i know stuff all about su carbs)
if you could think of any other thine it could be please help?
I know its not a 1200 but it is still in the datsun family please help guys

www.classiczcars.com

They are the orthority on Zs! A great group of blokes.

Sounds like carbies? I dont know anything about round top SUs eaither. Maybe try adjusting the jets? Under the carb

i tryed playing with the idle nut on the bottom of the carbs bt it didnt seem to make any difference

you shouldn't be "playing" with anything when it comes to zeds. liable to muck something up when you don't know what you're doing

anyway, triple webers would sort out your problems

My guess is if it was tuned to run ok with a vaccy leak, after you fixed the vaccy leak, that carb is now way too rich (as you suspected) I am sure there is a tech page here somewhere for tuning su's - same principles 1200 or Z

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one day, one day

OK, I said I wan't going to do this, but here goes.

From your description, I am guessing that the engine developed an air leak into the manifold [which you subsequently found & fixed] & some brilliant type has corrected the lean mixture by some truly clever means, rather than finding & fixing the actual fault.
My first guess is that he has lifted the needle in that one carb by removing the needle, then placing the little circlip on a lower groove.

Next, ..you come along & rectify the air leak, forcing all of the airflow to pass through the carb again, so there is no longer a weakening [leaning] of the mixture at that carb. End result? You now have one carb running rich.

If you wish to explore this avenue, you woulld need to remove the tops of the carbs, one at a time, starting at the back, to see which groove is used on the needles in these carbs. If the first two are the same as each other, then use this as a guide for the front one.

I recomend dismantling & reassembling only one carb at a time. If the third one is different from the others, then reset the clip to match. Be very carefull as the clip is small & excedingly easy to lose. I did such a job on my carbs with everything inside a plactic bag once, & sure enough I droped the clip. I was so glad that I took the precaution.

If you do not know how to do this, then get a workshop manual for any Datsun model that came with these Hitachi's, including the series 1 Bluebird [it was an international workshop manual]
Try not to learn by doing without some idea of how it all works beforehand.

That's my 2c worth.

P.S. I have assumed that your engine has three carbs.

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no zeds only have twin su's.
i now have a work shop manual so i will get stuch in to it tomorrow afternoon
thnx dodgeman i hope that is the problem then it is an easy fix

Sorry, I remembered this photo from the Goulburn Datnats & forgot about the other stock ones.

thats cool