You probably need to massage that nikki in order to get the air you will need with larger jets. Its not as simple as just upping the jets sizes, plus each engine is different. You will not get a recommendation to a specific jet size so you can minimize your spending, sorry. Likely you will want to buy a range of jets once you have the carb modified for the higher air/fuel needed for the SP you have.

 

Those aren't jets at Mazdatrix. They are shaped like air bleeds and don't flow fuel very well. They are meant for weber carbs. They are sized every .05mm which is kinda wide. They just happen to fit, more or less, in a Nikki. I bought some in the past but I would never use them now. Waste of money.

I'll echo what TG said. You don't change jets in your carb as a means of upping the power. All you do are doing is making it leaner or richer which isn't really helpful unless there is an actual reason to do so. I change jets at the very end of a long list, rather a file cabinet full of mods I do on my carbs. Jet changes are almost an afterthought and only necessary to get the AFR I want.

You are asking what I recommend for a stock Nikki? Stock friggin jets.