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Got a 73Z with 72 carbs.The three front sparkplugs (towards the front bumper) are black when they are removed from the engine for viewing. Is the front carb the culprit? I really don`t have the ba**s to adjust the carbs. It seems as the carbs go so goes the engine performance. Comments, suggestions? MikeT 73

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Mike: Check out ZTherapy.com for an excellent video that costs under $20 delivered to your door, that describes in great detail how to adjust the round top SU's.

It does sound like the front carb is running rich from the black (sooty) plugs in #1,2,3 cyls. Give it a try, you'll probably be amazed how easy it is to adjust them once you have "the knowledge" from Scott @ ZTherapy. I was!

Good Luck!


Carl Stahlnecker

72 240Z "Bambikiller"

HLS30-55703 11/71



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  • 1 month later...

I have the same car (73) with the same carbs (72) and a similar problem.....NO amount of leaning the mixture by screwing the choke tube/needle valve seat assembly in (up) seems to be able to get it lean enuf...what are we doing wrong?

In my case adjusting the mixture makes no differance from 5 turns out to all the way in????????

Tim Brown


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