In profound embarrassment, I come to you. . . . . . (starting up)

[Brandis]

Although BSAs came to me later in life, after Triumphs, Nortons, Vincents and the odd Matchless, when you get past the mechanical details, they all start and run the same.   So, I can't get old #280 to start.  (Not helped by the fact that my leg is not up to starting a tight motor so my son comes over.)   Here's where we are at:  It ran briefly so we assume things from that.
It has good and equal compression so we think the basic mechanical and valve timing is OK.
Magneto got the full rewind and all that by a professional shop that also does aircraft magnetos.  Good spark.  I've set the gap to .012. Kill button disconnected just to be sure.  Plug leads in correct orientation but reversed them just out of a sense of caution. I double checked the spark timing, points break at 5/16" BTDC.  And yes, magneto shaft rotates opposite direction from crank.
I bought a new Amal Premier carb just to be sure.  Plugs do not appear to get as wet as one might imagine after full choke.  I do the standard float tickle. 

[Triton Thrasher]

If the plugs are not wet, tickle it a lot more.

[muskrat]

G'day Jock.
New cold motors like a very rich mix. As TT says tickle it a bit more. Check for air leaks at the manifold, both ends, makes the mix lean.
Try a bit of "Start Ya Bastard". https://tinyurl.com/yb27sf28
Cheers

[KiwiGF]

It might be as simple as giving it 1/4 throttle when kicking it over…counter intuitive on a new motor I know, you may also have the tickover (throttle stop) in a too low position given its all new.

Its unlikely given the new carb but it could be worth checking the fuel level in the float and, related to that, that the float bowl vent is not blocked.

I guess if the tank has been lined the tank filters could be blocked? Or worse the lining’s dissolved and blocked carb jets?

[WozzA]

My old plunger would never start with full choke..   
   1/2 choke & she'd fire up 1st kick   

[CheeserBeezer]

I built a new bike a while ago and had a struggle getting it going. I'm with Kiwigf on this one. Keep turning the tickover screw up until it fires. Tickle the bike up until fuel comes out of the tickler button or the back of the carb.

[Swarfcut]

  The unholy trinity of mechanical, electrical and fuel strikes again!!!!  You need sparks in the right place, easy to time up on the wrong side of TDC. Sounds as if the basics are correct, so I'll concur with a lack of combustable material in the right place.

 Old time trick was to take out the plugs a give a good dose of fuel into each cylinder, then a good kicking with various amounts of throttle. Any sign of life and you know the mechanicals are fine, the ignition is working and it is a fuel problem. Two handed, (a kicker and a sprayer) and it should keep running, even if the carb is not providing fuel.

  Previous posts show the wisdom of hard won experience, all are valid considerations.

  Do not hang back on words of encouragement. Holler the brand name of Musky's spray.....real loud, show who's boss.


 Swarfy.