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Carbs set full lean, still running rich


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#1
bkelly

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This is driving me nuts. I rebuilt both carbs, set them full lean and they're still running rich. The car is running so rich, it can not idle. Any ideas?

#2
e_racer1999

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did you check and make sure that the needle is going all the way into the nozzle? did you make sure your needles are true?
Jason King
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1996 Infiniti I30 *I finally have all Nissans again!*
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As unfortunate as it may be, if you want to vintage race, go Euro....If you want to race for real, stick with the Z!


#3
Arne

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The adjusting knobs on the nozzles are for fine-tuning only. The main adjustment is the fuel level in the float bowls. Sounds to me as if your floats are not adjusted properly. Floats are adjusted too high.
Arne - Former owner, HLS30-37705, 7/71, 905 Red
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#4
Zs-ondabrain

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remove the top of the carbs (big round bell shaped peice) and check the seating of the needle. The best starting point is to hold the sleeve (with the needle attached) upside down, with the needle pointing upwards, the needle goes from pointy tip down to a thicker shape, it will then have a flat lip that should be level with the flat surface of the sleeve.

If not, then loosen the screw on the side of the sleeve and use a flat metal plate or ruler to seat it flush and then retighten. Do this to both needles on both carbs and carefully re-install them back into the carbs, while paying close attension to how easy the sleeve rises and falls as you tighten down the tops. then replace the oil that came out when you turned the sleeves upside down.


Pics should help

Picture 1 shows how to adjust it,
picture 2 is a decent picture of the same,
picture 3 is showing how to raise and let fall the needle while tightening the top dome down.

Dave.

Attached Thumbnails

  • needle placement.JPG
  • needle placement 2.JPG
  • rise and fall.JPG

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#5
e_racer1999

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if you haven't already invested in the ZTherapy vids, i recommend you do so....
Jason King
6/72 240Z / HLS30 89646 (Yellow)
1996 Infiniti I30 *I finally have all Nissans again!*
1971 510 4door (wife's car)
IZCC Member #14186

As unfortunate as it may be, if you want to vintage race, go Euro....If you want to race for real, stick with the Z!


#6
hd240z

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Just to cover the basics, are you sure the carb choke cables and nozzles are in the up position (warm)?
71 240Z HLS30 021986 (2/71 build) with 63,XXX miles

#7
Art@NissanSport

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Sounds like float issues. I just went through all this. The ZTherapy videos are good but do not explain the updated way to adjust the floats. I had Steve talk me through it and it made all the difference in the world.

#8
bkelly

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The needles are fine.

The chokes are disconnected...it came that way. Should the lever be pulled all the way back or forward? (this is my first car with a manual choke...or even a choke for that matter)

How are the floats properly adjusted? I just read something about putting an 1/8th drill bit under the float and bending the metal "pivot" so it just sits on top.

#9
hd240z

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The needles are fine.

The chokes are disconnected...it came that way. Should the lever be pulled all the way back or forward? (this is my first car with a manual choke...or even a choke for that matter)

How are the floats properly adjusted? I just read something about putting an 1/8th drill bit under the float and bending the metal "pivot" so it just sits on top.


If the choke cables are disconnected it doesnt matter where the lever is. When the cables are connected the console lever will be forward for the "choke off" position and the nozzles will be tight against the bottom of the carbs. I believe the nozzles are spring loaded and should be held in the up position with the cables off, but Im not absolutely sure of that. You might want to check to see if you can move the nozzles up and down by hand.

I've not had to adjust my carb floats so I cant help you there. Others here on the board can probably answer that question.

Good Luck
71 240Z HLS30 021986 (2/71 build) with 63,XXX miles

#10
DaveN

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A spring in the choke linkage on the side of the carb holds the nozzle up. The cable can be disconnected but the final link to the nozzle has to be attached. If it isn't the nozzle can drop far enough to cause an extremely rich mixture.

3 possible causes in the float bowls --

1. Sticking (open) or defective needle valves.

2. Defective floats. They're rigid urethane foam with a very thin skin. If defective or damaged by rough handling liquid gas can fill some of the cells, making the float lose bouyancy.

3. Levels set much too high. With the bendable metal arm on the float just touching the needle (but not compressing the spring in it) the measurement from the other end of that arm (on top of the float) to the underside of the bowl cover should be 13.5-14.5mm. That's 1 mm higher than the spec in the 70-71 FSM, per a tech service bulletin issued in early '73.

#11
justin260z

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A spring in the choke linkage on the side of the carb holds the nozzle up. The cable can be disconnected but the final link to the nozzle has to be attached. If it isn't the nozzle can drop far enough to cause an extremely rich mixture.


I dont understand that.^ I am having the same exact problem with my su's too. and my choke cables are gone too. My car will idle, but when I get on it, it blows black smoke like there is no tomorrow.

Im getting like 12 mpg too.

#12
Art@NissanSport

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I will try to explain how to adjust the carbs as best as possible without visuals.

Take the top of the float bowl off. If it's a 4 screw SU this is easy since you don't need to take the carbs off. If its a 3 screw SU, it might be easier to take the carbs off the mainfold.

1) Unscrew the top of the float off. And of coarse unhook hoses(unhook the hose from the fuel rail side because you will need it attached to the float top).

2) Hold the float top with the float attached vertically straight up and down so that the hinged part of the float is at the top. Using the attached fuel line hose, blow into it while at the same time starting to tilt the float towards your right (holding float in left hand) When it is staiaght up and down you should not be able to blow air throught it. But as you keep tilting it there will come a time when air will flow. Once this happens, back up a little bit (less lean) and blow air until you get back to the same spot. This is just a double check to make sure you know exactly where the air started flowing.

3) Once you have got the exact spot use a 1/2" drill bit to measure the space. The space should be a hair over 1/2". Adjust accordingly by bending the plate that attaches to the float.

This is not an exact sicence but it will get you close enough. It did the trick on my Z and now it runs great.

#13
bkelly

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The floats/needle valves are brand new so they aren't defective. I'll try to adjust them later on today. If this doesn't work, there's a guy that can work on them, but he's almost 2 hours away. He also welds so if it has to go that far the floors might as well be fixed (need some small patches) and the 1/4 will be replaced with a donor. I just hope this simple running rich problem doesn't lead into an all out restoration. I'm sure everybody has had the "While we're doing this, we might as well do that" syndrome.

#14
geezer

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Here's how Nissan suggested adjusting floats.

#15
Friar-Tuck

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BK,
I had an extremely rich condition due to the fact my #1 carb jet was well below top of the carb body due to the fiber/washer it rides in had never been run fully up in the lean position. I had to soak it in WD-40 a few hrs to soften it and (with difficulty) run it up full lean and then back it out 2 turs to start tuning. Is the distance from the carb body to top of the jet approx. the same distance in both carbs?
I had to remove the carbs and dissasemble to finally track down that gremlin.
Have a peek down the body at the jets and see if they are approx the same distance down the body from the throat.
The tail end of a caliper might fit between the carb body wall and the jet or...
even the little red spray straw from a can of WD and a small sharpie to mark the "straw" with.
Good Luck,
Tuck \o/

#16
justin260z

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i found out my carbs have 2 different sized jets. Where can i purchase new ones?

#17
e_racer1999

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jets or nozzles?
Jason King
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1971 510 4door (wife's car)
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As unfortunate as it may be, if you want to vintage race, go Euro....If you want to race for real, stick with the Z!


#18
justin260z

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the things that screw into the top of the bowls.

#19
Arne

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i found out my carbs have 2 different sized jets. Where can i purchase new ones?

Seems to me that that was normal for some years of roundtops, '72 three-screw I believe. But don't hold me to that.
Arne - Former owner, HLS30-37705, 7/71, 905 Red
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#20
JimmyZ

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Here's how Nissan suggested adjusting floats.


Nice Geezer! I like stuff like that! Was that out of an FSM or another publication?
What caught my eye was that the fron and rear carbs had different heights. Beats the sh!# out of the Haynes manual. Thanks.

Jim
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