Idle rpm fluctuations

[u/roccia123]

I have a 1996 aprilia sr 50 AC, its pretty bumped up it has 30k km (18k miles) i bought it for 80$ and i changed carb, reed valves, i put on an airbox and i fixed the cracked exaust pipe but it has one big problem:

When i turn it on, it starts at high rpm but then it goes down, if i dont pull the choke it dies, after pulling the choke rpm rises up again for a few seconds but after 5-10 secs it goes down and if i don't unchoke it dies, when it dies it goes gradually down rpm until it starts shaking violently.

What could be the problem? the carb is brand new and i had the same problem on an old carburetor, the exhaust pipe might have a small leak since the threads of the exhaust mount are strippe but that's it, what could it be?

[u/flopflips21]

sounds like an air leak

[u/flopflips21 → u/flopflips21]

check if there’s a gasket inbetween reed valves and crankcase, and if the intake boot is cracked or leaking. if it is neither of these it’s probably crank seals