1995 300Tdi diffiucult to start

I've just replaced the head gasket (3 piece gasket) on my 300 Tdi as it blew last week. I also had the head skimmed just in case. The Head went back on Friday & it started & ran OK.
The only problem is, that after the car's been standing for more than five or six hours, its difficult to start. Turns over for about 20 seconds, then splutters into life, with some blackish smoke from the exhaust. Once started though, it runs as before, no problems & no smoke.
Any ideas anyone?
Thanks, Kieron

Keiron, check the glow plugs

Any signs of fuel on the head? Sounds like you're getting air in somewhere - next time you leave it try priming and bleeding the fuel filter before you try starting it. If that sorts it or you find a bit of air in there you've got a low pressure leak somewhere. Could be the fuel return pipes from the injectors aren't done up tight enough.

have you checked the leak off pipes for signs of wear?

As above, check the leak off pipes. The 300 engine cover wears these through.

Also make sure all your fuel delivery pipes are tight, and that you havn't put a pin-hole in with a jubilee clip or similar. You have air getting in somewhere!

When you leave it, the diesel trickles back down the pipe, so when you start it, it has to pull that fuel back up again.

A big thanks to all of you for your advice. I'm going to carry out all the tips you have given me on Saturday & I'll post the results. Once again, thanks all.

Any luck with this as mines doing the same?

finate - have you tried the above suggestions?

I had issues with air in fuel supply, found that opening up bleed screw on top of fuel filter with engine running sorted things out

Looks like my starting issues are a dodgy starter motor... it got sticky today!

On another note anyone know how to drain the oil out of a 300TDI gearbox? Is it the 32mm bolt? If so mine's stuck! I take it the transfer box is the 17mm hex bolt on the bottom to drain and the square bolt on the back to fill up?