Another Z with starting issues

[Jeff Berk]

I need help getting my 260z with round-top SU’s running again.

Symptoms: It cranks and pops but no start.

Leading up to this, the engine would stumble. This was after I did some work on the car and I’m assuming caused the issue. In order of repairs, there’s the list:

1) Replaced the transmission.

2) Replaced the intake/exhaust manifold gasket.

3) Replaced the oil pan gasket.

4) Adjusted valves, discovering a damaged cam lobe. Spark plugs were coated with carbon, so I cleaned them with a propane torch.

<this is when stumbling was first notice, but car not driven since before transmission was changed>

5) Removed rocker in contact with the damaged lobe for inspection and reinstalled.

6) Retorqued intake/exhaust manifolds and discovered several loose nuts.

7) I tested the vacuum that showed an average vacuum of 12 in Hg at 1300 rpm and 13.3 in Hg at 1570 rpm.  

😎 I pulled the car out of the garage and turned it off. Later, I was unable to restart the car.

9) The spark plugs were removed and had gas on them. The fuel pressure gage showed 4.5 psi and I can hear the electric fuel pump running.

10) The Mallory Unilite (LED triggered) distributor’s ignition module tested out as working.

11) The Mallory 29440 coil is assumed to be working because a spark tester showed spark at cylinders 3 and 4.  I didn’t test the other cylinders for spark.

12) Firing order was checked.

13) I don’t expect the timing has changed on its own, so I don’t want to mess with it. Also, for some reason, I have yet to find the timing mark on the harmonic balancer.

The car is due the week after next to have the mechanic that installed the cam shaft repair the damaged cam shaft so worse comes to worse, I can have it towed in.

Any idea what I should try next?

[Mark Maras]

I'd drop the fuel pressure to around 3.5 psi and install a new set of spark plugs.

[Jeff Berk]

1 hour ago, Mark Maras said:

I'd drop the fuel pressure to around 3.5 psi and install a new set of spark plugs.

Thanks, I'll give that a try. 

[Jeff Berk]

Its still running very rough. I suspect that maybe I knocked something out of whack with the carbs when I removed/reinstalled the intake manifold. Like I said above, It's going in to the mechanic for repair of the cam shaft so I'll have him look at the SUs. He knows them inside out.

Thanks for the help.

[siteunseen]

It's hot out and I'm bored. Scary situation.

Did you ever see if it's the front 3 cylinders or the rears that are rough? The front carb runs 1-3, rear 4-6. You may be running on 3 cylinders?

The front carb has that vacuum advance nipple that needs to be hooked up or capped off. 

3 day weekend boredom. Goodluck with it, I'm sure it's something simple.

[Jeff Berk]

I just checked and the vacuum nipple is capped off. I tightened another vacuum connection (braided hose connected to the vacuum balance tube). I was able to keep the car running by using the fast idle adjustment screw.

The engine is missing but I cannot isolate which cylinders are missing because its not missing consistently. 

I re-balanced the air flow between the carb's because I wanted to do something as long as it was running.

I got the fuel pressure down to 3.5 to 3.75 using the pressure regulator. A previous owner removed the fuel rail and disconnected the return line so this is a "dead head" system. I'm going to try and put in a new fuel pressure regulator with a return once I get the car running and the cam shaft issue taken care of.