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260z with 240z round tops and a mild cam, what would be an ideal carb needle?


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with this setup current my SU’s are cranked all the way to the top, idle screws set as low as possible, and it’s still idling at 2000rpm and incredibly rich, so i’m thinking when i ordered a carb rebuild kit i bought the wrong needle? could someone please recommend me an appropriate needle for this setup?

 

Kind regards

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On 5/30/2020 at 4:27 PM, bunkhouse said:

 What needles are you using and have you set the float levels. The float level is the primary mixture adjustment.

 

Not sure what needles they are, i just bought a 240z carb rebuild kit on ebay, float level is reccomended to be set at 14-15mm so i set both at 14.5

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On 5/31/2020 at 7:45 AM, jonbill said:

if its idling at 2000, your first problem is too much air, not too much fuel. 

 

 

how could i reduce the amount of air going in? i’ve tried spraying started fluid all around the intake & manifold and nothing causes a rise in rpm, should i try with the air cleaner fitted ?

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On 6/1/2020 at 3:19 PM, bunkhouse said:

Two interesting problems. Plugs are black, idle is too high. Jonbill is correct about too much air causing the high idle and it must be getting too much fuel judging by the plug color. Describe your carb rebuild. What did you take apart and reassemble? Did you interchange any parts from one carb to the other?

 

it wasn’t a full rebuilt i just bought a refurbed set of su’s on ebay and some how the needles were bent. i’ve sprayed started fluid all around so i know there’s no vacuum leak

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6 hours ago, bunkhouse said:

 Raise both pistons with your fingers and let them drop. You should feel considerable resistance when raising them and they should both fall at the same rate and hit bottom at nearly same time.

 

Yep they both are hard to raise and fall slowly, have correct oil in dashpot 

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My guess is its running rich because you have the wrong needles/did not install them properly. My suggestions:

 

Check that the needles that came with the carbs match (if you can still read the markings) then throw them in a drill or dremel and straighten them out by hand (you do not need a lot of speed for this so be careful that you are not removing material). When you change the needles back to the originals are you still running rich?

 

For the high idle, remove the center linkage between the carbs and see if it still idles high. The 260Z linkage has a nub on the linkage for the front carb that keeps the front carb slightly open. I had to sand it down for the engine to idle at a reasonable speed. 

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