I have just purchased a 1971 240z with an l28 engine I found a vacume leak at the base gasket of my front 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 you 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 (round tops)

if you could think of any other thing it could be please help?

Sounds like you need to balance them.

Try reading this:

http://www.classiczcars.com/forums/showthread.php?t=11755

or this

http://www.teglerizer.com/sucarbs/techtip6.htm

Get a Factory Service Manual and no worrys .Hell it show's you how to do the job...( that's the engine L24 series.....Page EF-17.....For model L20a and L24 Series.......

thanx guys i will be taking them off and cleaning them out this week end because they have been sitting for over a year

Been sitting for over a year would be a clue..... When you are in the wash-up mode make sure your get the needles and seats flushed out well as old gas can get things varnished up.

Dissassemble one carb at a time. Clean it. Then you can use the other carb as a referance when you reassemble.

is there ment to be a gasker in the suction chamber because mine dont have one

i found the problem and it was totaly unrelated it is just a coincidence that my condensor in the dizzy packed up at the same time i fixed the vacume leak. However the carbs are still runing rich so i was wondering with the mixture nuts screwed to the top towards the carby is that lean or rich :?:

The mixture adjustment is turned counter clockwise to lean and clockwise to richer. To start with turn them counter clockwise to the stop and then back them back down, or clockwise 2 1/2 turns. This should get you on the right track. You then can balance the two carbs with the uni-sun to get the correct air flow between the two . With out properly balancing the two carbs you will find it impossible to set the mixture properly . Also check that the choke cables are not sticking when you turn off the choke. One more thing , you could have a nozzle sticking down when you turn off the choke . If the nozzle sticks down it will cause a vary rich mixture in that carb. Gary

i have done every thing you mentioned exept balenceing the carbs. I should

be getting a balencing tool verry soon.

i have the mixture nuts nearly all the way to the top and it is still blowing black smoke

Check to see if your choke is stuck. There are nozzles at the base or each carb and assuming the choke if off, then they should be all the way up, which is what you are adjusting when you turn the mixutre nut.

i have done every thing you mentioned exept balenceing the carbs. I should

be getting a balencing tool verry soon.

i have the mixture nuts nearly all the way to the top and it is still blowing black smoke

If you turned the mixture adjustment nuts counter clockwise , or up . all the way and you are still running rich , as Colorado said, check to see if the nozzles are stuck down. Just reach under the front of the carb to where the small fuel hose connects to the adjustment and push it up with your finger. If it snaps up then the nozzle sticking in the problem. One more thing , if the float in one or both of the float bowls is set too high or has sunk to the bottom or maybe just stuck open the raw fuel will run into the intake and flooding will also happen . One last thing , if the little fuel lines that run from the float bowl to the adjustment are stiff or brittle , this will cause the nozzle to stick. DO NOT REPLACE THIS HOSE WITH VACUUM LINE OR NON GASOLINE RATED HOSE. buy THIS HOSE EITHER FROM ZTHERAPY OR NISSAN . Auto parts store hose is too stiff and will not work properly. If you have a HOBBY store in your area , ask for gasoline rated hose and not plastic. too much heat from the headers or manifold. Try a cycle shop also . We have covered about everything that will cause the rich condition. That I can think of. Gary

i thought i found the problem but i was wrong it is still running realy bad i have replaced the points, plugs, leads, dizzy cap, rotor button, condensor,

coil, i have checked the float levels i cleaned out the carbs i have adjusted the valve clearance but yet it is still missing realy bad. It still runs better if you give it a long spark. It is runing extreamly rich. i have used quater of a tank of fuel just siting in my drive way i am thinking it may be a vacume leak but dont know how to find it. i have tryed spraying areo start around all the gaskets but there is no change so i give up i am takeing it to the mechanic on monday