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Trouble Getting '73 Hybrid Starting and Running

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Hi, I'm fairly new to this forum and the world of Z's, but I'm hoping for some advice on what to attempt next.
I picked up a '73 240z with a large list of modifications, including the SU carbs from a '72, and a "fresh built" l28 engine and head. I've done a small set of fixes and minor modifications to get it running, but as of yet have only had momentary success, and I have a suspicion that the electrical is to blame for the behavior. I've got a Pertronix electric points system installed, with the flamethrower coil that accomponies it, and have confirmed I'm getting a spark. I just replaced the old fuel pump and have it measured at about 3.5psi, checked for any obvious vacuum leaks, put new gaskets on the floater bowls on the carbs, and played with the timing to see if that was the issue, but no luck. 
I've managed to get it started and idling, but only once, and after no changes, it refuses to again for more than a few seconds. I've tried with and without the ballast resistor, and am going to try some new plugs today, but I just can't seem to pinpoint the issue.
Are there any obvious fixes I'm looking over that could be suggested, or common problems I might have looked over? I desperately want to get this beautiful old car back on the road, and would hugely appreciate any and all suggestions. Let me know what information/pics I can provide to help, and thank you in advance.

Edited by perspectiveshifting
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Seems like you're focusing on spark but the problem might be with fuel.  You said it started and idled, and that you have spark.  How old is the fuel in the tank and carbs?  How strong is the spark?  Strong and blue or weak and orange?  Modules have been known to partially fail.


You might check spark and timing would be with starting fluid.  Have someone squirt a few shots in while trying to start and have them try to keep it running with the fluid if it catches.

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What would be extremely helpful is what makes you think things are ok.


You said you have spark, but as newzed points out is it a strong spark? How did you check the spark?


You said you have 3.5psi of fuel pressure, but where do you have that fuel pressure? Can you see fuel flow? What kind of gauge are you using? Factory fuel rail?


What are the condition of the plugs?


Can we get a few pictures of your setup?


Newzed is definitely on the right track. Engine needs fuel, air, spark, and compression to run. Without one of those you are not going to get very far. If you have indeed checked the spark aspect, you have to make sure the timing aspect is correct. If you have checked that you are getting fuel pressure, you have to check that you are getting a steady fuel flow. You can bypass air and fuel by using ether, so you are left with spark and compression.


Checking valve clearance, timing, spark order, spark strength should help narrow down the problem.


You shouldn't need a ballast resistor with the 280z wiring harness. Make sure you haven't ordered a 6 volt coil or something of that nature. You should be all 12v.


Holler if you need a hand, plenty of helpful people here, but we can only help if you supply as much information as possible.

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