Vapor lock questions for the hotter climate guys

[Mark Maras]

 Zed, Thanks. The Nissan bulletin is great reading. A great description of the difference between vapor lock and percolation. It does sound like percolation is the problem.

[jalexquijano]

this is correct. The guy in the video fabricated too nice heat shields for me and send them by post. At least the car rpms drop to 200 and rise but the car does not stall when it is under the sun on heavy traffic. Now we need to move on with a nice hose replacing the rail. Any comments on this:

 

 

[jalexquijano]

The plugs fouled dry black. I cleaned them with a brass brush. however i shouldnt be doing this as the heat extensions i installed and provided by the youtuber were manufactured to solve this idle drop problem when sitting on traffic jam.

 

As stated before I parked the car and opened the engine door so heat started to get out. i took one picture of the fuel filter once i opened the engine bay and took another one after a couple of minutes running the car parked in idle. the rpm started to become stable at 800 to 900 rpm and did not dropped. So i think i still need to move forward and swap the metal fuel line with a modern approach rubber hose or remove the fan clutch and install a dual fan with shroud kit and relay. I would like your opinión on this. I want to feel secure if i get stuck in traffic and tackle this issue which is surely  percolation and nothing else! I even took out all the spark plugs and they were all fouled. I will not drive the car with the front Hood open, there must be a solution to get the heat out at traffic jams.

[Mark Maras]

 If the engine temp. remains normal in traffic, there's no need to alter the fan. Change the fuel line location. That's where the heat problem is located. According to the info supplied by Zed, the percolation problem is forward of the mechanical pump, Concentrate on that section of the lines.

[jalexquijano]

22 hours ago, Mark Maras said:

 If the engine temp. remains normal in traffic, there's no need to alter the fan. Change the fuel line location. That's where the heat problem is located. According to the info supplied by Zed, the percolation problem is forward of the mechanical pump, Concentrate on that section of the lines.

Should i replace the fuel rail that is fastened to the cam cover with other type of hoses? I have already wrapped it with a heat isolation cloth as per the second picture. Problem is still there. Once in traffic for more tan 15 minutes idle starts to fluctuate from 900 to 200 rpm randomly as temperature starts to rise. Once you place your foot on the accelerator it starts to become stable. Thats the reason i try to use the car only during night or on Sunday as there is no traffic.

If this is the solution, i would like to invest in nice hoses and fuel rail as the last picture shown.  Do you concur??? Anyone else?

[Mike]

Tagging @Bruce Palmer from Ztherapy to see if he has any advice.

I haven't gone through the entire thread, but, have you checked the carb fluid levels and the needles to make sure they are up to spec?  The SU linkage looks fairly shiny, so, maybe you're running with a rebuilt set of carbs?  I would also try running without the air filter to see if that changes the behavior.

[jalexquijano]

Yes both of my SU carbs were remanufactured completely from scratch by BRUCE PALMER and have SM N27 needles.  I am using Automatic Transmission Fluid as carb fluid oil. Nobody seems to have a solution for this strange problem as it only happens when the car is sitting under the sun at idle!

[Mark Maras]

 Just received my copy of "Datsun 240Z, Engineering Development. The Journey from Concept to Reality" by Hitoshi Uemura. In chapter six he this to say about vapor lock  issues.  Nice to know that the hot start issue ended with fuel injection.

 "After the 73 model year started to be sold, Nissan Motor Corporation, U.S.A. reported complaints that when the steering wheel was turned rapidly after driving in extremely hot regions, engine problems developed, and, at worst, the engine would just stop. They also reported that once the engine stopped, the customer had to wait in the car, without air conditioning and under the blazing sun, for at least 30 minutes until the engine cooled and could be restarted, which naturally increased complaints.

 We hurriedly conducted a test on the chassis dynamometer to reproduce the symptoms. After the vehicle had been run at 62 mph (100 km) continuously in  104`f (40C) temperature, it was taken out to the test course and the wheel turned rapidly. This confirmed that the engine problem occurred and at worst the engine stalled. The cause of the problem was vapor lock, in which gasoline vaporizes in the fuel lines and carburetor because of the high temperature in the engine bay. Lacking liquid fuel, the engine stops running. 

 Executive Director Ryoichi Nakagawa, the chief of the engine departments, gave us a pep talk, saying, "In a car, the worst case that can happen with this defect is the engine stalling, but if this happens on a plane, it crashes." Although the engine design departments also tackled countermeasures, satisfactory results were not obtained, and the manager Harada of the Third Design Department asked us to cooperate in coming up with countermeasures for the vehicle itself. 

 As a temporary measure, a heat shield plate was placed between the exhaust system and the carburater, glass fiber was wrapped around the fuel system pipe, and louvers were cut in the engine hood to vent heat. But this was not enough.

 Then, as a last resort, a powerful sirocco fan, which began to turn when the temperature in the engine room rose above a given temperature, was installed in the engine room to pump out the heat. This almost solved the problem, but it was never perfect, because the fan would turn for a while or sometimes started turning suddenly even after the engine was turned off, surprising drivers. Assistant Department Manager Shidei, who was the chief engineer at this time, visited America to persuade Nissan Motor Corporation U.S.A. to deal with the problem using this tentative measure for a while until a proper countermeasure could be taken. I can't imagine that would have been an easy task for him.

 One year later, we solved the problem properly by abolishing the carburetor and adopting the L28 engine with electronic fuel injection." 

Edited October 15, 2016 by Mark Maras

[siteunseen]

I wonder why they vented the hoods in '77?  I personally don't like water getting in my engine bay like it does through those.  Mine are loose too and sorta float/wiggle when I'm speeding.

[Mark Maras]

1 hour ago, siteunseen said:

I wonder why they vented the hoods in '77?  I personally don't like water getting in my engine bay like it does through those.  Mine are loose too and sorta float/wiggle when I'm speeding.

 Executive Director Nakagawa, chief of the engine department, trivialized the problem, in the beginning by saying that, at least the car wouldn't fall out of the sky, like a plane, if the engine died. He then offed the problem onto the body department. They may have waited until 77 to vent the hood because they were waiting to see how effective the engine mods would be. Little to no success in the engine department led to vents in the hood being tried and kept but ultimately they had to resort to a fan.

[Zed Head]

They're two different problems, aren't they?  The EFI cars certainly don't stop dead when  turning the wheel after driving in hot conditions, and stay dead for 1/2 hour.  Actually I've never even heard of that for the carb'ed cars.  Kind of a weird story.

They traded one serious problem for a serious annoyance, I'd say.

[Zed Head]

And the hood vents seem  like one of a series of attempts to stop the new annoyance.  By the time they were done they had a webbed intake manifold, more heat shields, added a fan, and maybe even lightened up the exhaust manifold.  The 77 manifold seems much more massive than the 78 and later exhaust manifolds.  Eventually they moved the exhaust ports to the other side of the head.  Seems like that trail of frustration would have been a good story for the book.

If they had designed an intake manifold that fit on the bottom and exhaust on top that might work.  They should have tried that.

p.s. thanks for typing in all of those excerpt words.  Tired fingers.