xtz 660 won't start - carb problem?

[jontyboy1979]

I've just changed the carb on my '92 xt as the original carb need a good clean and the choke was jammed. The new unit is off a 1998 bike and is clean and in good condition. However, the bike is refusing to run. It started last week but kept wanting to stall. I had another go at it today and now it only starts for an instant then dies and refuses to fire up again. After leaving it 5 mins it'll do the same again. There's a good spark, and there's petrol in the tank! There's 2 things I'm unsure about - 1) should the pump let fuel through when the engine isn't turning over? I pulled the hose off the carb and fuel was trickling through. 2) I haven't got hoses on the overflow pipe or the air vent pipe - does that make any difference? Apologies for my ignorance...Any suggestions apreciated!