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Hello all,

i'm from Australia and a few months ago i brought a '77 260z. after a few weeks i noticed that when the car got up to about 90degrees celcius it started running like it was starving for petrol when i accelerated. it only ever happens once the car reaches this estimated temperature. now both myself and my mechanic are scratching our heads as to what it could be, as it apparently isn't a blockage of the fuel lines, and doubtful that its vapour lock. the car can still be driven through the problem but its a pain. we have replaced the fuel pump, filter, etc. tried different coils and replaced points and condenser. my mechanic says all the spark points are fine and he doesn't think its anything mechanical. one of my friends said to check the twin su's and said thats what he thought it might be but ive had them tuned. other than the problem the car runs beautifully. any help would be appreciated.
 

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Ahh yes, the dreaded flattops!? The 73 240 and the 260 suffered severely from this type of problem. While it may not vapor lock it still may percolate the fuel in the lines and fuel bowls. It can happen on the roundtops too but nowhere near as severe. Make sure that BOTH mechanical and electrical fuel pumps are working. Insulate the fuel lines (if not already), make sure you have a fan shroud, a good operating fan clutch, and a FULLY functioning cooling system, and consider adding a pusher fan in front of the radiator that will kick on with a/c compressor, or if, you reach 180d F (sorry don't have my converter for temps and you know us Yanks!). If you have an aftermarket a/c system that has the compressor mount on the r/h side of the engine you may want to remove the mechanical fuel pump and just run an electric one in the rear. Do not remove any heat sheilding from below the carbs. Sometimes setting the floats at the MAXIMUM spec'd height in the fuel bowls helped. This is one of the main reasons that Datsun went to fuel injection. I have NO IDEA why they decided to run carbs in the rest of the world when they had such a good f/i system running on USA and Canada versions (they did run f/i in Canada didn't they, during this time frame?). There are some flattop experts on the forum so you may get some other good replys. Keep the engine and carbs coooooool.
 

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I had the same problem for 2 years on my 260. Had triple mikunis, but have since change just about everything fuel related. When I blocked the return and added a fuel pressure regulator, problem gone. Seems the fuel was just "bypassing" the carbs when the temp went up (SW Georgia). Now running DGV's almost tuned in. Hope this helps.
JeffK
 
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