Engine stops when engaging 1st

[Sannox]

Hi all, been a while since I was last on, just finished rebuilding my 2002 Fazer, I did a full on strip down, engine out of the frame, everything stripped and cleaned, painted or replaced as required. Spent many an evening cleaning every last damn nut and bolt. Bike went back together ok, the problem I have is the engine cuts out when I select 1st gear. Before I get the obvious one, the side stand switch was stripped, cleaned, casing painted, reassembled and tested and was also tested once installed and tested again tonight, just in case, all ok there.
Is there anything else that would stop the engine when 1st is selected?