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Basic Carb Question.

411 Views 10 Replies 5 Participants Last post by  monkeybumps
Working on trying to get my 240 to not run so rich. I have been playing with getting the carbs adj. in all the guides/books i have seen so far they say to start with tighten the mixture nut or screw it to the top. putting it in that location make the car run rich?

so it would be the
tighter the mixture nut = rich?

if so how far out do you back these out for a good starting point?

thanks all.
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The mixture nut determines the position of the jet tube. Tightening the nut moves the jet tube up which puts it on the fatter part of the needle so less gas leaks past the needle == Lean. Loosening the nut moves the jet tube down to a thinner part of the needle so that makes the mixture Richer.

You tighten them up to the top just to have a starting point of reference. Usually you can then loosen them 2 to 3 turns and you will be in the ballpark (assuming your timing, valves, idle screws, ignition etc are close to correct) enough to get the car idling. Then you use your air flow meter (or color tune, or ear, or wideband O2, or dyno, or plug color or butt dyno or voodoo) to get the mixture dialed in and the carbs balanced properly. ZTherapy has a good site and video to get you going.

Good Luck!
last night i tightened them up all the way and it ran just fine, it really seemed like it was still rich, i was still getting smoke. In fact the smoke seemed to be worse. This all confuses me. the more i back them out the more i got backfire in the carbs, which means its lean?

My mixture nut is more of a plate than a nut. its a flat disc that has teeth to grab on a stop device. does this sound correct. its a 72 240z. i think its all stock except the trans and rearend.

should my next step be to pull the carbs off and take a look at things?
Plate, nut they vary between the years of the carbs but does the same thing. You might need to adjust your needle height. The plate/nut varies the nozzle height. Float level also needs to be checked. dampner level, or type of fluid ( ATF, 20w, 30w, 10-30w, etc). Balancing the carbs also needs to be looked at.

Just some suggestions to look at.

does anyone know of any guide or how to check the above list? it sounds like i might have the needle height set incorrectly. also i need ot check the float level, any guides on this? perhaps on ZTherapy?

thanks again!
how hard is it to remove and then reinstall the SU carb setup? I'm alittle worried that once i get the setup off the car i will not be able to rebuild the units..... i know that they are somewhat complex and have tons of parts.... is this something a new person to carbs could tackle?

thanks all.
Please let me second the above site mentioned by rspiecha, www.teglerizer.com, as I have found it very helpful. Print it out and you have your very own reference manual.
do i try to tackle this?
SU carbs are about as simple as you can get. if you have a manual or rebuild instructions you certainly should be able to rebuild them. You will probably wind up doing bwetter work than most mechanics do, anyhow!
best place for needles and other parts? i know that there are tons of different types of needles what do you people here use? i'm running a stock L24... for the most parts.

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