RE: Welcome to Club SAITO !
Yes it is common for the spray bar to have a slot cut in it like that. Most of the time it looks like a elongated diamond shape and not rounded like that one on yours. The pit on the end of the needle was there since day one. But the sensitive part is more towards the shoulder so it probably worked fine for you. Normally the split faces straight down from the top, so it points down. But with the Saito engines, the bottom of the carb is up, so you want to facing straight down towards the bottom of the carb, which would have it point straight into the intake manifold tube.
I would check the O-ring seals on the intake manifold and make sure the valve gaps are set OK. If the compression feels Ok, it may simply be a bad glow plug. I had a glow plug fail on my Saito 80 once. It would light up and glow nicely but the engine would not fire at all. i put in a new glow plug and it fired right up and ran fine. Sometimes the glow plug element gets too contaminated and it doesn't initiate the catalyst reaction that lets the engine run.