Rubber/Plastic smoke coming from exhaust! A lot of smoke

Hello,

Today I finished breaking in my new cylinder/crankshaft and went for some fun. On a the roads I hit 105kmh easily. Everything was doing great. Then after I came down from a bridge (where I also drove 100+ kmh) and stopping at a red light, I started smelling rubber/plastic burning smell. Then I looked at my exhaust, it was smoking and smelling like crazy.

The smoke was also coming out of connection places of the muffler, so I quickly turned it off and inspected everything.

I have a pretty new exhaust, that hasn't seen a lot of rpm's with the 70cc kit. With 50cc I drove 2 days before my bike fell apart, and the exhaust hasn't gotten that much of heat.

It was still smoking like hell, even when I turned it off. The smoking decreasingly continued for like 3-5 minutes. Checked for dripping oil, loss of coolant, heat of the cylinder head, everything checked ok. The muffler was really hot.
After it cooled down, I turned on the bike, idled for a bit, gave it some rpm's, ran like nothing had happened. Drove home.

Could this have have been the muffler's cotton burning of the high heat? Plastic connections? Oiling from the factory for rust prevention? The exhaust is Yasuni R2.

Please help,
Thank you.

 

Probably just oil from the factory

 

Huge thanks for the reply! I actually remembered, that I drove a lot with a too big main jet! By that, I mean, it was spitting oil/gas from the exhaust. Also I mixed 40ml/L or 1:25 mix ratio for the breaking in period.