So very stuck... Any help is greatly appreciated

[andrew860]

So I picked up a complete Vento Zip (a 50cc 2 stroke Chinese brand scooter) at my local scrap yard. After a compression test, I quickly realized something was wrong with the piston/ rings / cylinder. I ordered a replacement cylinder, piston and rings and put them on. Compression is at about 90 psi now which i know is low but I figured it’s still high enough we’re it should start, even make a couple “ pop “ noises at the very least but still nothing. It has spark, it’s getting fuel and it’s getting air. I cleaned the magneto (I’m not sure if that’s what it’s called, the magnet thing that spins on the fly wheel and has something to do with timing) 2 stroke engines are usually very simple to me but this time I am at a complete loss and I am not sure what else to try. It doesn’t have a battery so I have been trying to start it with a jump pack and the engine turns over... and over... and over but nothing else will happen. Since I can’t think of anything else to try I was hoping someone on here had a idea. Thanks in advance for any help.

[ncsteve]

Here are some ideas: 
1. Is the fuel fresh?
2. Is the engine REALLY getting fuel? Is the float bowl full? Have you tried gas or starting fluid directly into the cylinder through the spark plug hole?
3. Is it a GOOD spark? Will it jump across a spark tester or a spark plug with the gap widened to 1/8" or more?
4. Is the spark occurring at the right time? Is the flywheel keyed in its proper place?

[Jwhood]

Did u put the piston in the right way, arrow facing down??

[supascoot]

Is fuel getting to the cylinder/plug. What was failure with old cylinder. Lean siezure??...could be manifold, reeds or crank seals. Try some fuel down plug see if it fires

[chehystpewpur]

check the reeds. the tips usually chip or crack and cause it to sputter pop or act like its running out of or getting too much gas and bog. ive had about 4 times that i scratched my head for up to a week and check them and they were bad. they are one of 3 mechanical motor parts that will make a 2t not run. the cylinder/piston exhaust and reeds.

[GrumpyUnk]

Have you tried some two-stroke fuel mix down the throat of the carburetor? Then give it a good kick or a few. If it is going to run, it will, repeat WILL pop on the mix. If it does not, check again for spark, dry plug, and if you need to replace a wet plug with dry, spritz some more, and kick. Key ON.
CHeck that the 'kill' switches are either flipped correctly or disconnected. SOME will not start with the kickstand down. They kill the sparky. Some won't crank, but can't tell if sparking cause it doesn't move.
If your compression is 90, that's pretty low. How easy was it to fit the rings/piston into the cylinder? It should take a little effort, and you should feel compression resistance if you crank the kick starter by hand or try to rotate the variator. If you cannot feel the compression stroke, it is too low to matter... and will likely not start.
tom