50cc engine stalls dead when back off at speed,no fuel start By scooterjoy (Read 430 times)

[scooterjoy]

So, I have a SYM jet 50, 2011. Its just had a new piston due to the old one spitting a chunk.need starter fluid to get her going and then she idles and runs great. You can slowly put around as much as you want but once you hold revs til approach top speed and back off, engine cuts out so abruptly the rear wheel locks up sometimes. I have a shark 50 that I pulled out of a forgotten shed with basically the identical engine so, joy. Is it the petcock? Why does the engine lock up? New piston/heavy compression? I would think it a wild piece of metal floating about and jamming valves or the piston itself except for it's a behaviour issue, its only when I let the revs build and the variator winds out and bang, dead in it's tracks, lights fail, rear wheel may lock, instantly. Omg please bestow your scooter know how upon me, I am your willing student, lols, but seriously, please, my son relies on the scooter for school. Thanks in advance.

[cyborg]

Except for the hard start I'd say you have an ignition problem,,,,that's the only thing that would cause an immediate abrupt engine kill

[scooterjoy]

well, after reading your reply, this morning i pulled the plug and it is fouled with cabon and even some oily deposits, thankyou, im thinking that i may have cylinder damage that the ring cant prevent oil passing through, i hope not, what do you think?
thanks again for your knowledge.

[cyborg]

Pull the air filter to see if it's plugged up

[scooterjoy]

Air filter looks good, might get a pod filter anyway.
So if I keep revving, twisting scooter won't die even at speed so I'm just using all of what's in bowl? My float seems to be operating correctly. I changed plugs. I took the carby apart and the small jet was blocked I've left it in carb cleaner, will try it again soon.

[cyborg]

Blast all the orifices with air before assembly,,,let us know how it goes

[greginnd]

Did you set or adjust the ring end gap when new piston was installed?