I got one of these Nostalgia 49 shipped here in Virginia earlier this year from Cajun Maddogs in Louisiana. I tried replacing the carburetor first to speed it up past 30 mph. I installed a PZ20 carb that has a metal choke lever that I like better than the plastic type on the other carbs. I had to trim the sheath of the throttle cable a little bit for the slide to be able to go all the way down in the carb. It greatly improved acceleration! It pops the front wheel off the ground sometimes shifting between 1-2 if the engine speed is not dropped before shifting! I have not installed the air filter that came with this carb kit. It still has all of the original air filter for now.
It still wouldn't go past 30 mph after upgrading the carb, so I knew the restriction was in the ignition. I replaced the 5 pin CDI with the racing one and it flys up to 40 mph or so. I haven't found decent roads and traffic yet to see if it can go any faster.
5 pin Racing CDI: