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Z runs like poop


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I recently got my Z started for the first time. I have a '73 240, with an '81 L28 (F54 block and P79 head). All block work has been done and new parts installed. Basically it is a new engine. I got original SU carbs from Scott at Z therapy, original 240Z air cleaner and ZX electronic ignition. Well the distributor and coil anyway.

I finally worked out all the trouble with the electronic fuel pump (Purolator 4psi, 30 gallons per hour) and put in a gauge to monitor this. So I finally start it. Really rough at first, but I follow Z therepy guide and balance my carbs, time the car. It still runs rough. It has no exhaust yet, just Motorsport 6 into 1 headers. It sounds like one of those gasoline rides at Disneyland.

What can I do to smooth it out? The car feels like it is getting too much gas. When I step on it, it slows down, yet when I back off the gas it will pick up. Also the clutch disengages too quickly, is there a way to adjust this? Should I regulate the line down?


"Go into emptiness, strike voids, bypass his defences; hit him where he does not expect you" -Lao Tzu

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If you're stepping on the gas and it runs slowly (lugging down?) then it's probably somewhere in the fuel system.

Try different settings with your carbs. Keep in mind that not all SU's are the same. Older ones are more sloppy and need more TLC and newer (rebuilt) ones are closer to spec.

Just because someone says, "back the mixture screw out 3 turns," ... doesn't mean that your SU's will run correctly at that same measurement.

A lean mixture will seem to run fine in the garage, but will sputter with a load (driving). Rich mixtures will sputter, smoke, and possibly blow fuel out the sides.

Take your air cleaner off and keep it off until you get a "feel" for the SU adjustment process.

Adjusting dual SU's isn't easy. But, doing it correctly can certainly be considered an art-form.

Practice with lots of different settings. Always start too lean or not-enough fuel/air. Then, work your way up.



Mike Gholson

1971 240z, Mikuni Carbs, Tokico 5-way Adjustable Struts, Ferarri Yellow, Stock Engine, 15x9 wheels w/50 series Falken tires, Currently being restored.

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  • 1 year later...

It sounds like your carbs are out of adjustment.

I too purchased some carbs from Z therapy. And I tried to adjust my carbs according to the Hayes manual. Needless to say I had the same problems you are describing. The problem was that the needle jets were of a different profile than stock making the stock adjustment impossible. I took my car to a shop where they measured the exhaust mixture and adjusted the carbs. It came to about 4 1/2 turns from bottom. Good luck.

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I got a email saying someone responded to my post the other day and I'm like "When did I post?". Of course this was over a years ago and my Z did run like poop then. Come to find out the cam timing was way off (try 15 degrees). Once she was lined up my Z came to life. I am having a bit of a new problem now though, howbeit a minor one.

My Z recently started running a little warmer than normal. Just a a millimeter or two right on the temp gauge but enough to notice. Now I do have a bit of an oil leak but this should not affect the temp should it? I have been dealing with this oil leak for over a year now and never has the temp came off dead center before. Radiator is new, well last year anyway. Water pump is new, topped off the coolant. Its like just enough to but you, alot!

Any ideas here? What would make a Z start running a few degrees hotter?

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  • 5 weeks later...
Originally posted by Timberwolf

I got a email saying someone responded to my post the other day and I'm like "When did I post?". Of course this was over a years ago and my Z did run like poop then.


We just got done making changes to the 240z Club website. This change is bringing a lot more traffic to our forums. Good things come with hard work... :)

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