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Discussion Starter · #1 ·
Help needed desperately,please.My 76 260z is pushing its luckAbout every week for the past several months I've been dropping a plug on either cylinder five or six.Theres no noise from the rockers,and very little oil is used.I've changed the points,leads,condenser and distributor cap.Im begining to think the problem could be fuel related.Cylinders four,five and six are always black and sooty,while one,two and three are nice and grey.Maybe its time to use my flat tops to hold me against the tide when I take the boat out.Any suggestions will be greatly appreciated.
 

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Sounds familiar - I've had virtually the same problem on my 260 (UK registered 1979), although I have 240Z carbs on it. I reckon your back carb is out of adjustment so needs looking at. Also check for sticking choke (ie jet not returning properly when choke turned off). The flat-top carbs are generally regarded to be crap - especially when they go wrong!

I'm no expert, but that's what it sounds like to me!

Good luck!
 

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Hi Jock6357.
Mr Tony Lamb appears to be right on the money. I would also give your baby a compression check to insure that a stuck or sticking valve is also not causing you trouble. Have fun. shane-
 

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Jock, sounds like you are eliminating the problem areas. Question have you adjusted the valves? Just because they are silent dosn't mean that all is good. How ever from what you have posted it strongly looks toward the flat top carb. If you can get your hands on a set of round tops I think you will be much happier with the performance. My 73 has the SUs ,round tops , and runs strong,I am not familure with the tuneing of the flat top carbs., but check the choke linkage to be sure it is not sticking in the on position . The su has the jet that lowers when the choke is used , and when it is discontinued some times they can stick causing the mixture to be vary rich for the 3 cylinders. Mine did this acouple of times before I figured it out, somthing to look at anyway. If you have access to a 79 or later electronic ignition ,this is a also avary good modification. I have no idea where you live but here in Portland Ore. SUs and the Ignitions dont seam to be hard to come by , at least for now. Good luck ,Gary
 

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Discussion Starter · #6 ·
For starters,I'd like to thank Tony,Shane,Z-Quest and Gary for your helpful advise.Well done and thanks.As for the questions that were raised.I've checked the compression Shane and all cylinders were within ten PSI of the required specs.Z-Quest,Australian Z's don't have a transistorized ignition.Later models I cant say though my 76 doesn't.As for spare parts Gary their starting to get a bit like hens teeth(Bloody hard to track down)here in Sydney,other parts of Australia I couldn't say.Reguarding the vaulves,they were my fisrt suspect.Though I wasn't going to pull the head off until I'd checked all the other possiblities.
I've removed the carbies,and found on both the choke valve and the throttle valve settings are out of wack.I've also removed the base of the rear carb to discover the float only stops when it reaches the top of the chamber.So hopefully I've found my problem.
Anyway thanks again and I'll keep you posted.
 
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