LEEFUNGCHOW says your timing is too advanced. blown head gasket at high speed: instant seize, happened to me on the freeway recently. it looks like your detonation has been occuring for a while.
FACT: CDI units can be faulty and go bad overnight. i have seen this happen way to many times. often janky wiring and faulty grounds can kill a cdi instantly. I bet your hpi may have locked on full or mid advance.
you need to be running ground wires directly to your motor and not your frame. i do it on all my bikes now. even points setup too. you should check your timing with a timing light and check your curve. (if it has one) might as well double check.
Fuck advancing your timing to the max anyhow dude. i'm all about full retard. keeps your motor cool as fuck, makes your top speed ultra fast, but it makes your powerband kick in real late. so i think the perfect balance is to retard until you can't pull into your power band, and then slowly start advancing till you hit it. High rpm advance will kill your moped and you will never go as fast as you really can.
i'm going to retard my timing today
sux about the reed cage. why do they not have stops? whats up with boyeson reeds not having stops? why do reed chip like that? in my polini 4 petal, i am using stock polini 2-petal reeds. i took them out, replaced them with some .45 reedstock, chewed those up in 100 miles, and put the old ones back in and they are still perfect. must have 1000 miles at least on them. no way. more than that. whats up with reeds?