Engine Problems...

Recently, I have encountered a problem with the engine. It all started when I took off the exhaust manifold to get to a core plug which had popped out due to frozen water (Most likely). When it came to re-assembling it, I made sure that I had tightened everything up pretty well, but haven't torqued them, as I don't currently own a torque wrench.

(I wish!)

 An SU Carburettor[1]

I went to turn the key and nothing happened, usually it sparks up first time but for some reason, it didn't. So I pulled out the choke and it roared into life, I thought "Its going nicely now", so I put the choke back and the engine cut out. I tried it a few more times and this kept happening, so, the next day I re-did all of the work, taking off the manifold and Carbs again, but this time used some silicone based gasket sealer, once again, I put it back all nice and secure, left it for a bit so the seal would dry, and turned the key. Once again nothing started, pulled out the choke and it started happily, put it back in and it cut out again. So I am wondering if I haven't got the carburettors tuned to the right fuel to air mixture, or a valve is loose. It might be I need to torque everything to the correct Nm (Newton Meters), but I'm sure I will find out what's wrong with it soon and its something I will take from my experience and use the knowledge I have on further cars I own/restore.

If anybody has any idea what this problem could be, please comment, It would be most helpful, thanks!

[1] SU is an abbreviation of 'Skinners Union', the company who made them.