I don't know by the number which version this is but by the age I'm guessing that it's a black carb version.
The little K&B's love the nitro and will respond well to any extra. 45% is a good place to start as it's good for sport running or racing and not as finicky on a hot day. Going lower is no problem either but keep the oil percentage at 18-20%.
3-1/2 turns out on the needle is a good place to start then adjust from there. K&B used to advise 4-1/2 turns but I found that it was too rich there.
www.mecoa.com may still have the owners manual for that engine online.