Ah, the saga of Nordwest starting
They could go sulky if left for just a week in cold weather.
My memory dredged up this from GeN#6:
"So, here is what appears to be the best strategy for persuading a reluctant Nordie into life. I shall christen it the Braham-Lishman method:
1 Petrol off.
2 Loosen float bowl drain screw to
release 'stale' fuel.
3 Petrol on for a few seconds to flush
carb.
4 Re-tighten drain screw
5 Petrol on, Choke OFF
6 Try a whiff of throttle , if no go
7 No throttle, pull choke out slowly
while cranking until engine fires
8 Find best choke position to keep
engine running."
So some nice fresh premium (actually 'super' would be worth the extra in this scenario) unleaded is well worth a try. Having said that, as Overbomber points out, you also need a good spark.
I used to have lots of trouble persuading the tuned 604 in to life when cold. That was CDI not Inductive ignition but I found it was sensitive to the air gap between the rotor 'pips' and the ignition sensor - particularly if there was a bit of surface rust on the rotor!
Even then, if it was a cold day the first attempts would sometimes only eventually produce impressive backfires.
This was with Keihin CR33s not a Teikei OEM carb so the dreaded gummed up passage in the standard carb setup wasn't the issue (See 'That Starting Problem' in GeN#7 for David Champion's description of that). So I tried a grade softer plug and that did the trick. OK for hill climbs but I would swap back to standard grade when riding it on the road in the summer.
"Do not adjust your mind, there is a fault in the reality"
1957 175 Sport