Modern Vespa

I'm losing my mind over this. A few months ago it was hitting (claimed) 60mph on flat roads. Most everything has been upgraded (70cc big bore, 17.5 Del'orto, wild lion exhaust, etc.). I replaced the original intake manifold with a Malossi racing model and it hasn't run right since. Tried swapping the old one back in and it made no difference. Hard to imagine the manifold caused this but that's about when it all started going bad. Wasn't an immediate problem. Has been gradually losing power for months.

I attached a digital tach recently and it almost feels like I'm hitting a rev limiter at about 7800 rpm. I don't know what the peak engine speed was when it ran well but I'm pretty sure it was higher.

I've thoroughly disassembled and cleaned the carb (less than a year old). Tried swapping the main jet, replaced the spark plug (old one looked fine), messed with the pilot screw before returning it to where I started. Replaced the petcock in the tank as well as the fuel/vacuum lines (all looked fine). Tried riding without the gas cap on. Nothing helps. Sprayed carb cleaner to check for air leaks. No issues there.

Gas mileage dropped from high 50's to mid 40's so I'm probably not burning all the fuel. Engine temp hovers in the 130c area in 90f degree weather.

I'm running out of ideas. As far as I know the CDI is original. Engine is low on power but fairly smooth up till 7800 or so. Does this sound like a failing CDI? It's maybe the only thing I haven't replaced/upgraded yet. And if I'm replacing it is it worth going with a Malossi racing unit or should I just stick to stock?

Have you checked your belt and rollers? Didn't mention swapping those or your clutch springs.

Kevlar belt is about two years old. New delta adjustable clutch, flywheel, Dr pulley rollers, and multivar kit within the last year. Maybe 4k miles on the belt and around 2k miles on the rest. Haven't been in there since install. Seemed less likely considering their age.

If compression still tests ok, I'd zero on the clutch then. I've seen the clutch pad pivot pin circlips fail. Totally random WTF experience!