Cold Starts

Was wondering if anyone could give me some advice, thought there would be a few folks on here who might be able to help with an RB30 engine,

I have an N/A RB30 (SOHC) and am having trouble with cold starts, when the engine is warm it runs and starts fine,

However, when i kick it over for the first time in the day it takes a little while to kick over (cranks fine) but just dosent start, then when it does (after 4-5 goes) it sounds like it wants to die on me, and it idles very eractically for the first couple of mins,

For example,

The rev's increase, then they decrease and i think the car is going to stall (it dosent, but its sounds like its getting pretty close to stalling) and then does this again, takes about 5mins of warming it up before the engine starts to idle properly,

Its a stock RB30 from a 1986 VL Commodore, stock everything including ECU, Injectors etc..........etc, the engine is in my 260z and im using the stock in-tank fuel pump setup from a 1992 Nissan Pintara, I also recently replaced the water pump (which was awesome fun :-) but didnt change the timing belt,

Anybody got any ideas?

Or atleast where i should start