Fuel delivery issue of some sort

[trogdor1138]

I just purchased a 1971 240Z. Since I'm a brand-new owner I don't know many specifics about this particular car. The previous owner alluded that it had sat for some time, but every time I went to view and inspect the car he was able to start it. He told me there was an issue with 3rd gear, so I'm rebuilding the transmission and while I'm in there I'm replacing the clutch disc and pressure plate.

However, I've been unable to get the car to run for any extended period of time. He delivered the car to me by trailer at my house, so I haven't actually driven it. When he dropped it off the battery was dead; I was told the lights had been left on. When I hook it up with jumper cables I'm able to successfully crank the starter.

Now don't laugh at me (too hard) but this is my first car with a manual choke and my first one to work on with a carburetor. I understand the general principle: pull out the choke to start cold, then gradually push in as the engine warms. However, it's hard for me to get the engine to actually start. With a lot of experimentation with choke position and the help of some starting fluid into the carbs, I can usually get it to start. However, after a variable amount of time (5 to 30 seconds) the engine dies.

I've found with experimentation that if I lightly pump the accelerator (quickly but gently) I can get the engine to rev and can extend the time it runs for. If I simply press the accelerator the rev's drop until the engine dies. The car has a mechanical fuel pump that appears to be in good order. I had my wife crank the engine while I held a jar to the outlet hose of the fuel pump and good amounts of fuel squirted out. I believe this is a good indication that the lines are clear, at least enough for fuel flow. The car has a L24 engine and the head was replaced a few years ago.

If I understand correctly, pumping the accelerator manually pumps fuel into the carbs. Pulling the choke out causes the carbs to deliver a richer than normal fuel/air mixture. In my experimentation, the best choke position for starting on my Z is not all the way out but only part of the way.

I believe that the problem lies among the following:

-Bad gas in the tank. I added a gallon or so but this could have mixed with crappy fuel

-Carbs that are woefully out of calibration

-The car doesn't like me yet due to poor treatment by previous owners

I also have a few questions:

-Should the choke lever in the console travel the whole length of its track? Currently, mine only pulls out about halfway

-Any good methods of identifying if gas is bad?

-How can I adjust the carbs to get a reliable start? I just need a starting point, regardless of economy, from which to begin tuning

Any input is much appreciated. Feel free to mock my ignorance of carburetors

[trogdor1138]

By the way, I have the Haynes manual for the S30's and "How to Rebuild Your Nissan/Datsun OHC Engine". I am referencing these books, but real-world experience from others is always helpful.

[5thhorsemann]

That Haynes manual is kindling, search FSM and you will find a downloadable version herein. I would recommend you buy the Z therapy SU carb tuning video if your carb skills are as bad as you say. There is (are) no accelerator pump(s) on the SU carbs, so pumping the pedal does nothing but allow more air into the system. Also, put the air cleaner(s) back on and try to start it, the additional vacuum will draw more fuel into the manifolds.

Also, drain the tank and use that gas in your lawn mower, there is a plug at the bottom of the tank. This will show how much crap is in the tank. While you are down there inspect the hoses, specifically the vent hoses that run through the cars interior behind the tail light cover panel. Make sure the hoses are soft and pliable, if they are hard and rotten they are a fire hazard and will allow (more) fumes to enter the cabin. Then check to see if there is an electric pusher pump near the passenger side wheel well in front of the tank. Some of the pumps have filters inside, that may be clogged, or the pump itself may not work which will restrict or even prevent flow. This is standard stuff to do on the purchase of an old S30.

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[trogdor1138]

Thanks for the suggestions; I've actually got her up and driving now. The fuel tank and lines overhaul is on the to-do list.

I've actually ordered the ZTherapy rebuild kit, so that's the next weekend's project. As far as I can tell the carburetors have been woefully neglected and the choke is not correctly set up at all. I actually start better with the choke pushed all the way forward, even on a cold Utah morning. To get her started right now I have to lightly tap the accelerator while starting and then continue to do so for about a minute. Then I have to wait about 5 minutes at idling before being able to drive. It's a pain, but at least she starts!