Poor starting

[Matty30]

Hi, I've got a 325 convertible, it's been turning over a lot before eventually firing up, like ten seconds or more, ten seconds is a long time when starting. I've tried a few things.

Checked fuel pressure, fuel return valve, fuel pressure regulator and they're all fine so it doesn't seem to be a fuel system fault.

I changed all the spark plugs and gave it a new distributor cap and rotor arm, did nothing to help.

Then I checked compression and it was taking a while to build compression, so, I have put new rings on, new head and valve seals too but it still turns over just as much before starting.

Once it starts it runs lovely, however on first start in the morning it takes ten seconds or more to start, if left for half an hour or more it takes ten seconds to start. If I start it after just a few minutes it starts up with a couple of seconds.

Anyone got any ideas what it might be or what to try next?

Thanks in advance for any help.

[minesapint]

This sounds as though the fuel rail is losing it's pressure.
This could be the non-return valve is failing so the fuel in the rail & lines returns to the tank & on start up it has to fill & pressurize the system from scratch.
I would check after being left say overnight whether the fuel rail is still pressurized by splitting the line between the fuel filter & fuel rail, be careful as if under pressure will go all over the place, good idea to disconnect the battery.