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Vapor Lock


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My "Z" project is coming along fine. My daily driver is being a bit obstinate. I have a '87 sentra it seems to run fine until you shut it off in hot weather only. The fuel in the filter sucks back into the tank only when the temp is above 100. I have replaced fuel cap, all lines, fuel pump, purge canister and control valve, fuel filter and tank screen. It appears that the car starts and will run until all of the fuel in the carb bowl is used. I have to prime the carb six or seven time for the fuel to get back to the filter, then the car runs great until I shut it off again if it is still hot. If it is cool or in the evening the problem doesn't happen. I also tried to run with the fuel cap off, no difference. I would appreciate any thoughts on this problem. Stinkin' Mojave desert.

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Your diagnostic of "vapour lock" sounds right, but I think it's happening in the fuel lines around the hot engine and lines to the carbs.

Have you got a heat sheild under the carbs?

Put "heat wrap" around all fuel lines and exhaust manifold. I'm guessing you've got those 260z carbs, if so block off the extra water hoses that heat the carb bases (their only needed for snow areas ect)



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Thanks for your input. I am still trying to figure this out. last night I blew thru all the hard lines on the frame and did a visual inspection as well no blockages found. The '87 Sentra emissions manual is of no help. Keep thinking. - Tom

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HKSZ has the right idea unfortunately the non cross flow head of the Z makes it vulnerable to vapour lock. Ways around it are as follows.

Is your heat shield still on your Z? no PO's have removed it have they?

1.) Install Vented 260z-280z bonnet.

2.) Use header wrap around exhaust manifold.

3.) insulate fuel lines.

4.) replace your 260z cabs with Round Top 240z Style carbs.

Just a few things to look at a picture of your engine bay would greatly help with some diagnosis.

Sorry it's late and I'm tired I didn't realise it was your Sentra causing trouble not a Z.

I don't even know what a Sentra is :ermm: .

Good luck anyway.

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