Thanks for the ideas -I'll try them today.

Ahicks -yes I've been hand starting, although I have also tried using an electric drill to flip it faster but it never really sounded like it was firing when I used that. How fast does a starter spin the prop?
I also tried putting fuel in via the spark plug but that didn't help.
How much fuel do these engines use? I mean how do I know if it's pulling fuel through properly? Some fuel is definitely getting in but I don't know how to tell whether enough is getting in or too much (flooding the engine). The pulse port is doing something -as I can see a pulse down the short pipe between the base of the engine and the base of the carb.
I'm using a 5v power supply rather than a battery as it's running on a test bench -i've checked it sparks at speed (rotating prop with spark plug removed).

Tailskid, thanks for the technique - it'll be good to see if your version does the trick.

Some more questions:
-How can I tell if the engine is either starved of fuel or flooded? Is there something I should look out for to differentiate between the two?
-Is there a risk that the gaskets on the engine are leaking and I don't have a proper airtight block? Would that result in poor fuel pumping?

Thanks