Please help bike won’t run

[theguy2024]

I’ll try and make this as short as possible. Bought a 100/79cc niome kit from amazon like I always do decided to step into new territory and buy a basic reed valve (still don’t understand what these do) and was told to make a windowed piston. Decided to buy a PZ19 carb for more power not sure if that was necessary also bought a new pipe. Put everything together and the bike ran !! it was working fine but then it stopped running, would only spark for a bit then cut out. i’ve tried everything: Changing needle clip position, drilled slightly larger jets, bought NT carb and upped that jet, took off reed valve put piston port.

The last thing i’m thinking is that the windowed piston is giving way too much air so i’m gonna buy a new piston and not window it, not run reed valve or bigger carb and just do what i’m used to and if that don’t work i’m throwing this bike in the dump. Maybe I ported it wrong

 

[Greg58]

First if you ported it wrong it should still run since it started when built. I would start simple, change the spark plug and gap it from 26-28, check all connectors on the cdi and coil. I like to remove the magneto coil and sand the back to insure a good ground to the engine, sand both sides of the ground wire as well.

 

[Greg58]

If you remove the reeds you have to change the piston or it will not run, the piston skirt acts as a seal as the piston travels down pushing the fuel charge up the transfers,

 

[Greg58]

On a reed valve system the reeds do the sealing, think of the reeds as a one way valve, they let fuel mixture through under vacuum but close under back pressure preventing blow back which happens to some degree on piston port engines.

 

[theguy2024]

Thanks @Greg58 that makes a lot of sense. I noticed my CDI wires were melting on the head so this may be it.