I tried to look up other threads for this but might not have had my search terms correct since what I did find has not answered my question.

So I have an MC21 that I have been working on, refreshing different parts. When I first got it, before I changed anything, it would accelerate and flatten out/hesitate from 9k rpms to redline in first gear. It seems like after a few WOT runs it would clear up. I attributed this hesitation to dirty plugs or too much 2T oil. Also the RPMs were often slow to drop with the clutch pulled in. The latter I was told might have been from an air leak.

I recently tore it down to have bits repainted and replaced all the vacuum hoses, put in new plugs and changed the reeds and cage to the Tyga kit. Now that it is back together I am having the same issues. While the RPMs seems to drop slightly faster there is still an ever present flat spot in 1st and 2nd from ~9k to redline. Once I go from 2nd to 3rd, with RPMs up at least, it definitely has power and pulls how I would expect it to (and better than in 1st/2nd given the current problem). What is bothering me is why the power drop is only there in first and second? Where should I focus on next? It definitely seems to be isolated to certain gears.

The bike is stock except for the Tyga reed cage and a delimiter. The delimiter was installed after I got it and this did not seem to have an affect, positive or negative, to the way the bike was/is behaving.

Thanks!