I'd bet money it's a fuel issues. Those carbs really cause problems. I cleaned my stock gurtner over ten times before I got it running. And still ended up replacing it with a dellorto Sha 15:15.
If it ran at all, it's not timing stopping you. Is the choke on? Are you running the stock airbox/airfilter?
Try filling the float bowl manually maybe?
It just seems like you aren't getting enough fuel. Have you tried shooting some premix down the carb?