I have a smallframe 50s upgraded to 103.
The bike starts easy, runs good for about 2-4km and after that it can not work on high revs, but only with a gear engaged.
If I stop the bike and increase the rpm, it is ok.
If I engage a gear, it starts but when I try to increase the revs, it makes big BANG from the exhaust and it can not accelerate at all.
It just bangs and stalls.
The spark is very black after that and if I change it it becomes black again.
I tried to roatate with the idle screw and the mixture one but I just made things worse.
Also I noticed that the black rubber that connects the carb with the engine is torn on the outer part that is like a donut but not on the inner hose.
Should I change my carb to a bigger one? (I have a 19 now)
Thank you in advance.